Papers for Thursday, May 08 2025

In this work, we demonstrate that a dynamical dark energy component predicted by massive gravity gives rise to a distinctive evolution of the equation of state. This scenario is favoured over the standard $\Lambda$CDM model when confronted with the latest combined datasets from the Dark Energy Spectroscopic Instrument (DESI), the cosmic microwave background (CMB), and supernova observations. The model stands out as a rare example of a healthy, self-consistent theory that accommodates phantom dark energy while maintaining a technically natural, small asymptotic cosmological constant. Our analysis indicates a preferred graviton mass of approximately $5 \times 10^{-33} \text{eV}$, suggesting the emergence of a new cosmological length scale. This leads to a maximal deviation of the equation of state around $z \sim 2.5$, a prediction that will be robustly tested by upcoming, deeper surveys of baryon acoustic oscillations.

We present one of the largest uniform optical spectroscopic surveys of X-ray selected sources to date that were observed as a pilot study for the Black Hole Mapper (BHM) survey. The BHM program of the Sloan Digital Sky Survey (SDSS)-V is designed to provide optical spectra for hundreds of thousands of X-ray selected sources from the SRG/eROSITA all-sky survey. This significantly improves our ability to classify and characterise the physical properties of large statistical populations of X-ray emitting objects. Our sample consists of 13079 sources in the eROSITA eFEDS performance verification field, 12011 of which provide reliable redshifts from 0<z<5.8. The vast majority of these objects were detected as point-like sources (X-ray flux limit F(0.5-2 keV)>6.5x10^-15 erg/s/cm^2) and were observed for about 20 years with fibre-fed SDSS spectrographs. After including all available redshift information for the eFEDS sources from the dedicated SDSS-V plate programme and archival data, we visually inspected the SDSS optical spectra to verify the reliability of these redshift measurements and the performance of the SDSS pipeline. The visual inspection allowed us to recover reliable redshifts (for 99% of the spectra with a signal-to-noise ratio of >2) and to assign classes to the sources, and we confirm that the vast majority of our sample consists of active galactic nuclei (AGNs). Only ~3% of the eFEDS/SDSS sources are Galactic objects. We also show the diversity of the optical spectra of the X-ray selected AGNs and provide spectral stacks with a high signal-to-noise ratio in various sub-samples with different redshift and optical broad-band colours. Our AGN sample contains optical spectra of (broad-line) quasars, narrow-line galaxies, and optically passive galaxies. It is considerably diverse in its colours and in its levels of nuclear obscuration.

Population III stars, the hypothetical first generation metal-free stars, have yet to be discovered. Even after three years of successful JWST operations, studies have shown that most galaxies identified to date at $z > 5$ exhibit a metallicity floor of $Z\gtrsim2\%\,Z_{\odot}$, possibly due to unknown selection biases toward bright galaxies or rapid metal enrichment. To address this question, we search for galaxies with low R3$=$[OIII]$\,\lambda$5008/H$\beta$ ratios as part of the JWST Cycle-3 large treasury program, the Slitless Areal Pure-Parallel HIgh-Redshift Emission Survey (SAPPHIRES). Using deep NIRCam Wide-Field Slitless Spectrscopy (WFSS) data, we report the discovery of seven extremely metal-poor galaxy candidates in the SAPPHIRES Early Data Release field, with estimated $12+{\rm log(O/H)}<7.0$ at $z\sim5-7$, including two sources with $Z<1\%\,Z_{\odot}$, significantly breaking the metallicity floor observed both locally and at high redshift. These candidates appear extremely faint ($\sim28-30\,$ F200W AB mag) and low-mass (${\rm log}(M_{*}/M_{\odot})\sim6.8-7.8$), as expected from the mass-metallicity relation. They also exhibit very blue UV slopes ($-2.6\lesssim\beta\lesssim-2.0$), likely due to low dust content $A_{V}\lesssim0.2\,{\rm mag}$ or young stellar ages $\sim5-20\,{\rm Myr}$. Compared to galaxies at similar redshift, they appear exceptionally bursty in their star formation activity. Our results highlight the power of NIRCam/WFSS in identifying extremely metal-poor galaxies, from just a single pointing, with more data to come in SAPPHIRES. This underscores the potential of pure-parallel programs towards achieving JWST's primary science goal: discovering the first pristine stars and galaxies. Deep JWST/NIRSpec follow-up observations will also be essential to confirm their nature and perform detailed chemical abundance analyses.

Context. Galaxies in the Universe show a conformity in the fraction of quenched galaxies out to large distances, being quite larger around quenched central galaxies than for star-forming ones. On the other hand, simulations have shown that the clustering of halos and the galaxies within them depends on secondary properties other than halo mass, a phenomenon termed assembly bias. Aims. Our aim is to study whether samples that show galactic conformity also show assembly bias and to see if the amplitude of these two effects is correlated. Methods. We use synthetic galaxies at $z = 0$ from the semi-analytical model SAG run on the MultiDark Planck 2 (MDPL2) cosmological simulation and measure both conformity and galaxy assembly bias for different samples of central galaxies at fixed host halo mass. We focus on central galaxies hosted by low-mass halos of 10$^{11.6}$ $\leq$ $M_{\rm h}$/$h^{-1}$ M$_{\odot}$ $<$ 10$^{11.8}$ because it is a mass range where the assembly bias has been reported to be strong. The samples of central galaxies are separated according to their specific star formation rate and stellar age. Results. We find that the level of conformity shown by our different samples is correlated with the level of assembly bias measured for them. We also find that removing galaxies around massive halos diminishes the conformity signal and lowers the amount of assembly bias. Conclusions. The high correlation in the amplitude of conformity and assembly bias for different samples with and without removing galaxies near massive halos clearly indicates the strong relationship between both phenomena.

Recently, Currie et al. simulated the detection of molecules in the atmospheres of temperate rocky exoplanets transiting nearby M-dwarf stars. They simulated detections via spectral cross-correlation applied to high resolution optical and near-IR transit spectroscopy using the ELTs. Currie et al. did not consider the effect of unocculted star spots, but we do that here for possible detections of molecular oxygen, carbon dioxide, methane, and water vapor. We find that confusion noise from unocculted star spots becomes significant for large programs that stack tens to hundreds of transits to detect these molecules. Noise from star spots increases with greater spot filling factors, and star spot temperature has less effect than filling factor. Nevertheless, molecular oxygen, carbon dioxide, and methane could be detected in temperate rocky planets transiting nearby M-dwarfs without correcting for star spots. Water vapor detections are the most affected, with star spots contaminating the exoplanet signal as well as producing extra noise. Unocculted spots only affect transit spectroscopy when normalizing by dividing by the total flux from the star. We describe an alternate normalization method that minimizes star spot effects by deriving and implementing an unspotted proxy spectrum for the normalization. We show that the method works in principle using realistic levels of random observational noise. Alternate normalization would be broadly applicable to all types of transit spectroscopy, and we discuss challenges to applying it in practice. We also outline a comprehensive approach that has the potential to overcome those challenges.

We present ALMA CO observations of the molecular gas in a sample of 41 luminous unobscured quasars at z $\sim$ 2 from the Sloan Digital Sky Survey. 32 targets comprise the main sample observed in CO(3-2) and 9 targets have archival ALMA data of CO(3-2), CO(4-3) and CO(7-6). All quasars have rest-UV to optical spectra tracing ionised gas in the broad line region (e.g. CIV) and the narrow line region (e.g. [OIII]) and they cover the full range of outflow properties in the SDSS quasar population at these redshifts. 15 out of the 32 quasars in the main sample are detected in CO(3-2) and five out of the nine archival quasars are also detected in CO. The median gas mass for all 20 CO detected quasars is 8.0 $\pm$ 1.5 $\times$ 10$^9$ M$_{\odot}$ with a median M$_{dyn}$ of 1.4 $\pm$ 0.9 $\times$ 10$^{11}$ M$_{\odot}$. We find gas fractions in the range 0.02 - 0.32, which are generally lower than both inactive galaxies and obscured quasars at similar redshifts. We suggest an evolutionary trend in gas fractions of quasar host galaxies from obscured and gas rich to unobscured and gas poor. We note a tentative correlation between the gas fractions and the broad-line region properties with quasars showing high CIV blueshifts, indicating stronger broad-line region winds, having higher gas fractions. Six of the quasars corresponding to 15% of the sample also show evidence for at least one companion galaxy detected in CO at the same redshift.

The radiative transfer equation for spectral lines from an extended gas is derived from first principles, treating the gas as a system of many atoms/molecules rather than isolated ones. Line broadening effects are assumed to be dominated by particle motions (Doppler effect), but collisional broadening effects are included in the impact approximation. We retrieve the canonical radiative transfer equation under the condition that the optical depth over a coherence length, defined as the transition-levels lifetime times the speed of light, is much lower than unity. For other cases, the line radiative transfer equation contains a correction factor whose magnitude depends exponentially on the coherent optical depth. We compute that many-body effects affect line radiative transfer of strongly emitting and astronomically ubiquitous radio- and submillimter lines, such as the HI 21 cm line, and rotational transitions of the main isotopologue of CO. These results imply that care must be taken when interpreting observations relying on these lines, as many-body effects can significantly alter emergent line profiles and bias inferred physical conditions of the emitting gas.

Context. Elusive intermediate-mass black holes (IMBHs; $100~M_{\odot} \leq M_{\rm BH}\leq 2\times10^{5}~M_{\odot}$) can act as ``time-squeezing'' machines, enabling studies of AGN geometry through reverberation mapping (RM) on much shorter timescales than their supermassive siblings. Aims. The broad line region (BLR) radius constraints for IMBH candidates with different Eddington ratios probe the unexplored faint end of radius--luminosity ($R-L$) relations and allow us to build a robust $M_{\rm BH}$ estimator. This study aims to (a) confirm a rapidly accreting IMBH candidate; (b) demonstrate the feasibility of the first photometric BLR reverberation mapping (RM) campaign for this class of objects. Methods. The IMBH candidate J1448+16 was identified in the broad H$\alpha$-selected spectroscopic sample from SDSS. We carried out narrow-band H$\alpha$ and broad-band SDSS~g\'~monitoring to check small-scale variability and extract the time lag between the BLR and accretion disk (AD) continuum during 5 months (March--July 2024) using a 60-cm telescope at the Caucasus Mountain Observatory. Results. We confirmed the candidate as an active IMBH using XMM-Newton as a bright X-ray point source with the photon index $\Gamma = 2.32^{+0.15}_{-0.13}$, suggesting the high accretion rate. From a combination of SDSS optical spectra and XMM-Newton observations, we estimate the black hole mass in the range $\sim 0.9-2.4~\times10^{5} M_{\odot}$ and the Eddington rate from $\sim 37-112\%$. We report high-amplitude $\sim 60\%$ intra-night ($\sim 2$~h) H$\alpha$ variability in this highly accreting IMBH. In addition, we extracted a tentative measurement of a BLR RM radius $\sim 1-8~\mathrm{days}$. Conclusions. This work is a proof of concept for further IMBH variability studies and BLR RM campaigns, which will be essential for the calibration of the $R-L$ relation at the faint end.

We present the results of VLT/MUSE integral field spectroscopic observations of the Ly$\alpha\,$ emission nebulae associated with 11 high redshift ($z \geq 2.9$) radio galaxies (HzRGs) with DEC $<25^{\circ}$. When considering the other nine sources with available archival MUSE data, these observations increase the coverage to half of the currently known HzRGs. For two sources we are unable to confirm the original identification, as no Ly$\alpha\,$ emission was detected. We produce narrow band images centered on the Ly$\alpha\,$ line, extract their nuclear spectra, map their ionized gas kinematics, and derive the Ly$\alpha\,$ surface brightness profiles (SBPs). The SBPs are generally well reproduced by an exponential law with a typical scale length of $\sim 20-30$ ckpc. We measure emission line ratios finding most sources in agreement with an AGN origin for their gas ionization, with a single object hinting at strong star formation. Regarding the connection between the radio and ionized gas emission, we find that while the Ly$\alpha\,$ nebulae are preferentially aligned with the direction of the radio emission, there is no clear correlation in terms of size or gas kinematics, and only a weak trend connecting their radio and Ly$\alpha\,$ luminosities. The alignment is most likely the result of anisotropic nuclear emission rather than of a direct impact of the jets into the ionized gas.

We performed a comprehensive analysis of flux and color variability in a redshift-matched sample of Seyfert galaxies, comprising 23 gamma-ray-detected narrow-line Seyfert 1 galaxies (gNLS1s), 190 non-gamma-ray-detected narrow-line Seyfert 1 galaxies (ngNLS1s), and 10 gamma-ray-detected broad-line Seyfert 1 galaxies (gBLS1s). Utilizing multi-band light curves from the Zwicky Transient Facility (ZTF) in g, r, and i bands, along with mid-infrared (MIR) observations in W1 and W2 bands from the Wide-Field Infrared Survey Explorer (WISE), we observed that gBLS1s exhibit more significant variability than gNLS1s, while ngNLS1s display minimal variability across both optical and MIR wavelengths. The pronounced variability in gBLS1s may be attributed to a more closely aligned jet relative to the observer's line of sight or their comparatively lower accretion rates. In contrast, the subdued variability in ngNLS1s suggests that their flux changes are primarily driven by accretion disk instabilities. A significant correlation between optical and MIR variability amplitudes found here supports the reprocessing scenario, wherein variations in the accretion disk emission are re-emitted by surrounding dust. Furthermore, our long-term color variability analysis revealed a stronger redder-when-brighter (RWB) trend in approximately 35%, 61%, and 80% of gNLS1s, ngNLS1s, and gBLS1s, respectively, in optical wavelength, strengthens the reprocessing scenario with the observed trend of stronger RWB for approximately 68%, 96%, and 30%, respectively, in MIR wavelength. The prevalent RWB trend observed in both optical and MIR wavelengths from the current sample of Seyfert galaxies on the longer time scales is likely associated with accretion disk instabilities.

We implement a machine learning algorithm to search for extra-terrestrial technosignatures in radio observations of several hundred nearby stars, obtained with the Parkes and Green Bank Telescopes by the Breakthrough Listen collaboration. Advances in detection technology have led to an exponential growth in data, necessitating innovative and efficient analysis methods. This problem is exacerbated by the large variety of possible forms an extraterrestrial signal might take, and the size of the multidimensional parameter space that must be searched. It is then made markedly worse by the fact that our best guess at the properties of such a signal is that it might resemble the signals emitted by human technology and communications, the main (yet diverse) contaminant in radio observations. We address this challenge by using a combination of simulations and machine learning methods for anomaly detection. We rank candidates by how unusual they are in frequency, and how persistent they are in time, by measuring the similarity between consecutive spectrograms of the same star. We validate that our filters significantly improve the quality of the candidates that are selected for human vetting when compared to a random selection. Of the ~ 10^11 spectrograms that we analyzed, we visually inspected thousands of the most promising spectrograms, and thousands more for validation, about 20,000 in total, and report that no candidate survived basic scrutiny.

Coronal rain, observed in 3D spine-fan magnetic configurations, results from thermal instability in the solar corona, where runaway in-situ cooling causes plasma to condense and drain along the magnetic lines. The reconnection of the magnetic field lines around the null point creates jets, seen as denser structures traveling along the field lines. As these dense regions evolve, thermal instability can set in and ultimately form coronal rain. In this paper we study the importance of partial ionization effects in the formation of coronal rain in the late evolution of 3D spine-fan magnetic reconnection in the solar corona. We use a two-fluid model consisting of neutral and charged particles coupled by collisions, where ionization recombination processes are taken into account. To trigger the thermal instability, we here investigate how magnetic reconnection generates flows that lead to the accumulation of higher-density structures along magnetic field lines. The dynamics associated with the spine-fan magnetic reconnection produces current sheets around the null point and flows along the field lines. Blobs similar to coronal rain start to appear after 400 seconds in the simulation domain which follow the field lines from the direction of the perturbed null point. The temperature drop is accompanied by recombination of charged particles. Recombination effects become important in coronal rain evolution when the temperature drops considerably in the condensed structures. The neutrals are slowed down by recombination, producing decoupling in velocity at the size of the blob, but inside the condensing structure, the neutrals can move faster across the field lines, creating small scale structures. This study presents a novel two-fluid approach to coronal rain, showing that incorporating two-fluid effects is essential for accurately capturing its dynamics.

Deep astronomical images are often constructed by digitially stacking many individual sub-exposures. Each sub-exposure is expected to show small differences in the positions of stars and other objects in the field, due to the movement of the celestial bodies, changes/imperfections in the opto-mechanical imaging train, and other factors. To maximize image quality, one must ensure that each sub-exposure is aligned to a common frame of reference prior to stacking. This is done by reprojecting each exposure onto a common target grid defined using a World Coordinate System (WCS) that is defined by mapping the known angular positions of reference objects to their observed spatial positions on each image. The transformations needed to reproject images involve complicated trigonometric expressions which can be slow to compute, so reprojection can be a major bottleneck in image processing pipelines. To make astronomical reprojections faster to implement in pipelines, we have written `dfreproject`, a Python package of GPU-optimized functions for this purpose. The package's functions break down coordinate transformations using Gnomonic projections to define pixel-by-pixel shifts from the source to the target plane. The package also provides tools for interpolating a source image onto a target plane with a single function call. This module follows the FITS and SIP formats laid out in the seminal papers. Compared to common alternatives, `dfreproject`'s routines result in speedups of up to 20X when run on a GPU and 10X when run on a CPU.

Understanding the impact of neutrino masses on the evolution of Universe is a crucial aspect of modern cosmology. Due to their large free streaming lengths, neutrinos significantly influence the formation of cosmic structures at non-linear scales. To maximize the information yield from current and future galaxy surveys, it is essential to generate precise theoretical predictions of structure formation. One approach to achieve this is by running large sets of cosmological numerical simulations, which is a computationally intensive process. In this study, we propose a deep learning-based generative adversarial network (GAN) model to emulate the Universe for a variety of neutrino masses. Our model called $\nu$GAN (for neutrino GAN) is able to generate 2D cosmic webs of the Universe for a number of neutrino masses ranging from 0.0 eV to 0.4 eV. The generated maps exhibit statistical independence, lack correlations with training data, and very closely resemble the distribution of matter in true maps. We assess the accuracy of our results both visually and through key statistics used in cosmology and computer vision analyses. Our results indicate that samples generated by $\nu$GAN are accurate within a 5% error on power spectrum between k=0.01 to k=0.5 h/Mpc. Although this accuracy covers the mildly non-linear scales, consistent with other works and observations, achieving higher accuracy at fully non-linear scales requires more sophisticated models, such as diffusion models. Nevertheless, our work opens up new avenues for building emulators to generate fast and massive neutrino simulations, potentially revolutionizing cosmological predictions and analyses. This work serves as a proof-of-concept, paving the way for future extensions with higher-resolution 3D data and advanced generative models.

We present the results of a three-year X-ray, optical, and radio polarimetric monitoring campaign of the prototypical black hole X-ray binary Cyg X-1, conducted from 2022 to 2024. The X-ray polarization of Cyg X-1 was measured 13 times with the Imaging X-ray Polarimetry Explorer (IXPE), covering both hard and soft spectral states. The X-ray polarization degree (PD) in the hard state was found to be $\approx4.0\%$, roughly twice as high as in the soft state, where it was around $2.2\%$. In both states, a statistically significant increase of PD with the energy was found. Moreover, a linear relation between PD and spectral hardness suggests a gradual and continuous evolution of the polarization properties, rather than an abrupt change of polarization production mechanism between states. The polarization angle (PA) was independent of the spectral state and showed no trend with the photon energy. The X-ray PA is well aligned with the orientation of the radio jet, as well as the optical and radio PAs. We find significant orbital changes of PA in the hard state, which we attribute to scattering of X-ray emission at intrabinary structure. No significant superorbital variability in PD or PA was found at the period $P_{\rm{so}}$ = 294 d. We also find no correlation between the X-ray and optical polarization; if any, there is a long-term anti-correlation between the X-ray PD and the radio PD.

In recent years, weak lensing shear catalogs have been released by various Stage-III weak lensing surveys including the Kilo-Degree Survey, the Dark Energy Survey, and the Hyper Suprime-Cam Subaru Strategic Program. These shear catalogs have undergone rigorous validation tests to ensure that the residual shear systematic effects in the catalogs are subdominant relative to the statistical uncertainties, such that the resulting cosmological constraints are unbiased. While there exists a generic set of tests that are designed to probe certain systematic effects, the implementations differ slightly across the individual surveys, making it difficult to make direct comparisons. In this paper, we use the TXPipe package to conduct a series of predefined diagnostic tests across three public shear catalogs -- the 1,000 deg$^2$ KiDS-1000 shear catalog, the Year 3 DES-Y3 shear catalog, and the Year 3 HSC-Y3 shear catalog. We attempt to reproduce the published results when possible and perform key tests uniformly across the surveys. While all surveys pass most of the null tests in this study, we find two tests where some of the surveys fail. Namely, we find that when measuring the tangential ellipticity around bright and faint star samples, KiDS-1000 fails depending on whether the samples are weighted, with a $\chi^2$/dof of 185.3/13 for faint stars. We also find that DES-Y3 and HSC-Y3 fail the $B$-mode test when estimated with the Hybrid-$E$/$B$ method, with a $\chi^2$/dof of 37.9/10 and 36.0/8 for the fourth and third autocorrelation bins. We assess the impacts on the $\Omega_{\rm m}$ - S$_{8}$ parameter space by comparing the posteriors of a simulated data vector with and without PSF contamination -- we find negligible effects in all cases. Finally, we propose strategies for performing these tests on future surveys such as the Vera C. Rubin Observatory's Legacy Survey of Space and Time.

Striated granular edges observed in the solar photosphere represent one of the smallest-scale phenomena on the Sun. They arise from the interaction of strongly coupled hydrodynamic, magnetic, and radiative properties of the plasma. In particular, modulations in the photospheric magnetic field strength cause variations in density and opacity along the line of sight, leading to their formation. Therefore, the striation patterns can be used as valuable diagnostics for studying the finest-scale structure of the photospheric magnetic field. The Daniel K. Inouye Solar Telescope allows observations of the solar atmosphere with a spatial resolution of better than 0."03 with its current instrumentation. We analyze images acquired with the Visible Broadband Imager using the G-band channel to investigate the characteristics of fine-scale striations in the photosphere and compare them with state-of-the-art radiation-MHD simulations at similar spatial resolution. Both observed and synthetic images reveal photospheric striae with widths of approximately 20$-$50 km, suggesting that at least 4-meter class solar telescopes are necessary to resolve this ultrafine structure. Analysis of the numerical simulations confirms that the striation observed in the filtergrams is associated with spatial variations in photospheric magnetic flux concentrations, which cause shifts in the geometrical height where the emergent intensity forms. Some fine-scale striation in the synthetic images originate from magnetic field variations of approximately a hundred Gauss, resulting in a Wilson depressions as narrow as 10 km. This suggests that DKIST G-band images can trace footprints of magnetic field variations and Wilson depressions at a similar scale.

To identify long-period variable (LPV) stars in IC10 - the nearest starburst galaxy of the Local Group (LG) - we conducted an optical monitoring survey using the 2.5-m Isaac Newton Telescope (INT) with the wide-field camera (WFC) in the i-band and V-band from 2015 to 2017. We created a photometric catalog for 53,579 stars within the area of CCD4 of WFC ($\sim$ 0.07 deg$^2$ corresponding to 13.5 kpc$^2$ at the distance of IC10), of which we classified 536 and 380 stars as long-period variable candidates (LPVs), mostly asymptotic giant branch stars (AGBs) and red supergiants (RSGs), within CCD4 and two half-light radii of IC10, respectively. By comparing our output catalog to the catalogs from Pan-STARRS, Spitzer Space Telescope, Hubble Space Telescope (HST), and carbon stars from the Canada-France-Hawai'i Telescope (CFHT) survey, we determined the success of our detection method. We recovered $\sim$ 73% of Spitzer's sources in our catalog and demonstrated that our survey successfully identified 43% of the variable stars found with Spitzer, and also retrieved 40% of the extremely dusty AGB stars among the Spitzer variables. In addition, we successfully identified $\sim$ 70% of HST variables in our catalog. Furthermore, we found all the confirmed LPVs that Gaia DR3 detected in IC10 among our identified LPVs. This paper is the first in a series on IC10, presenting the variable star survey methodology and the photometric catalog, available to the public through the Centre de Données Astronomiques de Strasbourg.

To aid the interpretation of observations of substellar atmospheres, Mukherjee et al. (2024) created the Sonora Elf Owl grid of model atmospheres, simulations that accounted for disequilibrium quench chemistry. However, Sonora Elf Owl did not accurately estimate CO$_2$ quenching because the models quenched the gas with respect to the full atmosphere equilibrium, but CO$_2$ should have instead been quenched with respect to the disequilibrium (i.e., quenched) abundance of CO. As a result, Sonora Elf Owl under-predicted the CO$_2$ abundance by several order of magnitude in some instances, an amount that JWST is sensitive to. Here, we release version two of the Sonora Elf Owl grid which has corrected CO$_2$ concentrations. Additionally, in version two we remove PH$_3$ as a spectral contributor since our spectra consistently contained too much PH$_3$ absorption. The new spectra can be found as an update to the original Zenodo postings.

Based on the modern understanding of MHD turbulence theory, we propose a new method for measuring the spectral properties of magnetic turbulence by synchrotron polarization gradient analysis. Using synthetic polarization observational data, we first confirm the feasibility of the gradient technique to determine the scaling properties of magnetic turbulence. We then apply this technique to the Galactic plane survey data from the Australia Telescope Compact Array (ATCA) and obtain the power-law spectral feature of the Galactic magnetic turbulence of $E\propto k^{-10/3}$. Gradient techniques open up a new way to obtain spectral properties of magnetic turbulence from polarization observations, such as the Low-Frequency Array for Radio Astronomy (LOFAR), in the presence of low-frequency and strong Faraday depolarization.

The photometric and spectroscopic studies of six contact binaries were performed for the first time. The orbital periods of all the six targets are longer than 0.5d, and we discovered that their mass ratios are smaller than 0.15. So, they are extremely low mass-ratio contact binaries. Only one target is a W-subtype contact binary (ASASSN-V J105032.88+420829.0), while the others are A-subtype contact binaries. From orbital period analysis, ASASSN-V J075442.44+555623.2 shows no orbital period change. Three of the six targets demonstrate a secular period increase, and two targets for a secular period decrease. We investigated the LAMOST spectra employing the spectral subtraction method. All six contact binaries show no chromospheric emission line, implying no chromospheric activity. Their absolute parameters, initial masses, ages, energy transfer parameters, and instability parameters were calculated. The bolometric luminosity ratios ($(L_2/L_1)_{bol}$), the energy transfer parameters ($\beta$), the contact degrees ($f$), and the mass ratios ($q$) were collected for a sample of 218 contact binaries and we analyzed and discussed some correlations. The results by analyzing the relation between $\beta$, $f$ and $q$ indicate that the energy transfer parameter between the two components of extremely low mass-ratio contact binaries is independent of the contact degree. And the predicted cutoff mass ratio was estimated as 0.021 by analyzing the relation between $f$ and $q$.

We present the serendipitous radio-continuum discovery of a likely Galactic supernova remnant (SNR) G305.4-2.2. This object displays a remarkable circular symmetry in shape, making it one of the most circular Galactic SNRs known. Nicknamed Teleios due to its symmetry, it was detected in the new Australian Square Kilometre Array Pathfinder (ASKAP) Evolutionary Map of the Universe (EMU) radio-continuum images with an angular size of 1320"x1260" and PA = 0 deg. While there is a hint of possible H$\alpha$ and gamma-ray emission, Teleios is exclusively seen at radio-continuum frequencies. Interestingly, Teleios is not only almost perfectly symmetric, but it also has one of the lowest surface brightnesses discovered among Galactic SNRs and a steep spectral index of $\alpha=-0.6\pm 0.3$. Our estimates from HI studies and the Sigma-D relation place Teleios as a type Ia SNR at a distance of either ~2.2 kpc of ~7.7 kpc. This indicates two possible scenarios, either a young (under 1000 yr) or an older SNR (over 10000 yr). With a corresponding diameter of 14/48 pc, our evolutionary studies place Teleios at the either early or late Sedov phase, depending on the distance estimate. However, our modelling also predicts X-ray emission, which we do not see in the present generation of eROSITA images. We also explored a type Iax explosion scenario that points to a much closer distance of <1 kpc and Teleios size of only ~3.3 pc, which would be similar to the only known type Iax remnant SN1181. Unfortunately, all examined scenarios have their challenges, and no definitive supernova (SN) origin type can be established at this stage. Teleios's symmetrical shape suggests expansion into a rarefied and isotropic ambient medium. The low radio surface brightness and the lack of pronounced polarisation can be explained by a high level of ambient rotation measure (RM), with the largest RM being observed at centre.

We present a new way to identify systems similar to our Local Group (LG) of galaxies in cosmological simulations. Our method uses as a new constraint the speed and direction of the LG's center of mass, which we can measure accurately from cosmic microwave background data. When we apply these criteria to different cosmological simulations and compare the results with traditional selection methods, we find statistically significant differences. Our approach produces simulated galaxy pairs where the relative M31 velocity is less radial (2 to 10 percent difference over the mean) and more tangential (1 to 4 percent difference over the mean) than in cases that do not take into account the barycenter speed. The radial change pattern appears consistently across all cosmological models we test, showing that matching the observed barycenter velocity has a measurable effect when modeling and interpreting Local Group-like systems.

Since the variety of their light curve morphologies, the vast majority of the known heartbeat stars (HBSs) have been discovered by manual inspection. Machine learning, which has already been successfully applied to the classification of variable stars based on light curves, offers another possibility for the automatic detection of HBSs. We propose a novel feature extraction approach for HBSs. First, the light curve is transformed into the frequency domain via Fourier transform, then the amplitudes of the first 100 harmonics are extracted, and finally these harmonics are normalised as feature vectors of the light curve. A training data set of synthetic light curves is constructed using ELLC, and their features are fed into recurrent neural networks (RNNs) for supervised learning, with the expected output being the eccentricity of these light curves. The performance of RNNs is evaluated using a test data set of synthetic light curves, achieving 95$\%$ accuracy. When applied to known HBSs from OGLE, Kepler, and TESS surveys, the networks achieve an average accuracy of 88$\%$. This method successfully identify four new HBSs within the eclipsing binary catalog of Kirk et al. The use of orbital harmonics as features for HBSs proves to be an effective approach that significantly reduces the computational cost of neural networks. RNNs show excellent performance in recognising this type of time series data. This method not only allows efficient identification of HBSs, but can also be extended to recognise other types of periodic variable stars.

Sombrero-like galaxies exhibit unique structural properties that challenge traditional photometric decomposition methods. In this study, we investigate their structural differences using both photometric and kinematic approaches to assess the extent to which photometric decomposition may misidentify key components, particularly the stellar halo. We select 270 Sombrero-like galaxies at redshift z=0 from the TNG50 simulation, applying filters to include only those with stellar mass $M_{\ast} > 10^{10}M_{\odot}$ and stellar halo mass fraction $0.3 < f_{\rm halo} < 0.6$. Synthetic images are generated using the GALAXEV population synthesis code, and photometric decomposition is carried out on both face-on and edge-on views using GALFIT. We then compare these results with kinematic decomposition based on the auto-GMM method, focusing on differences in recovered structural parameters such as mass fractions and S'ersic this http URL-like galaxies typically consist of disks embedded in massive stellar halos and may account for 30-60% of galaxies in TNG50. However, their identification is complicated by structural degeneracies and the presence of disk features (e.g., bars, spirals, star formation) at low or moderate inclinations. In face-on projections, photometric decomposition systematically overestimates disk fractions as stellar halos are almost absent, while edge-on analysis provides only approximate halo fractions. Radial profiles show discrepancies between photometric and kinematic decomposition, particularly in central regions. Additionally, no conclusive link exists between the S'ersic index n and the presence of large stellar halos, challenging the use of n as a merger history proxy. These findings underscore the need for improved decomposition methods to better understand the complex structures of Sombrero-like galaxies.

The blazars are one of the leading candidate sources of high-energy neutrinos. Recently, two blazars have been found to be temporally and spatially correlated with some IceCube high-energy neutrino events. The two blazars, GB6 J2113+1121 and NVSS J171822+423948, are Flat Spectrum Radio Quasars (FSRQs) with redshifts greater than unity. In particular, NVSS J171822+423948 has a redshift of 2.7, which provides an important probe for studying the radiation processes of jets from active galactic nuclei in the early universe. To better understand the physical origin of the IceCube neutrinos, we adopt the one-zone leptohadronic model to fit the multimessenger emission of GB6 J2113+1121 and NVSS J171822+423948 during their $\gamma$-ray flaring periods and then calculate the high-energy neutrino detection probability. The chance of detecting a single muon neutrino from these two sources is found to be $\sim 2\%$ and $0.8\%$, respectively. Although such detection rates are not high mainly because of their high redshifts, our investigation strongly suggests that these sources are efficient PeV neutrino emitters. Our results also indicate that electromagnetic cascades produced by hadronic processes contribute significantly to X-ray and $\gamma$-ray emissions. However, high-energy $\gamma$-rays can be severely absorbed by the soft photon field from the broad-line region (BLR), which weakens the correlation between $\gamma$-rays and neutrinos, while suggesting a stronger connection between X-rays and neutrinos. We predict that IceCube will continue to detect neutrinos from FSRQs with redshifts greater than 1 in the future.

We present the first systematic study of bipolar outflows using HC$_3$N as a tracer in a sample of 146 massive star-forming regions from ALMA-ATOMS survey. Protostellar outflows arise at the initial stage of star formation as a consequence of active accretion. In general, these outflows play a pivotal role in regulating the star formation processes by injecting energetic material in the parent molecular clouds. In such process, lower velocity components of outflows contain a significant portion of the energy. However, extraction of those component is difficult as the corresponding gas is often mixed with that of the ambient cloud. In our sample, we identified 44 bipolar outflows and one explosive outflow in HC$_3$N (J=11--10). The host clumps of these outflows are found to be at different evolutionary stages, suggesting that outflows in HC$_3$N are detectable in different stages of star formation. Also, the non-correlation of HC$_3$N outflows with clump evolutionary stages suggests that HC$_3$N is an unbiased tracer of outflows. Analyses revealed that HC$_3$N performs slightly better in detecting low-velocity components of outflows than traditionally employed tracers like SiO. The derived outflow parameters (i.e outflow mass, momentum, and energy) show moderate correlations with clump mass and luminosity. Our analysis of outflow opening angles and position-velocity diagrams across the outflow lobes show that, HC$_3$N is not only a good tracer of low-velocity outflows, but can also detect high-velocity collimated outflows. Overall, this study indicates that HC$_3$N can be used as a complementary outflow tracer along with the traditionally known outflow tracers, particularly in the detection of the low-velocity components of outflows.

Magnetars are very rare astrophysical objects, with $\sim$31 known to date. They are best understood as highly magnetised neutron stars, but a greater number need to be found to constrain their role in stellar evolution pathways. We apply a novel approach for the detection of fast, transient X-ray sources, using a revised version of the EPIC XMM-Newton Outburst Detector (EXOD) with the aim of detecting and identifying new and rare variable compact objects. We detect a transient, variable source notable for its strong variability and hard spectrum. The emission from 4XMM J175136.8-275858 is well characterised by a blackbody, with temperatures between $\sim$1.8--5\,keV during its lower luminosity phase. Its temperature is poorly constrained during its brightest phase, and we observe an increase in luminosity by two orders of magnitude over timescales of a few ks. This is driven by increased emission of X-rays at energies above 2\,keV, with a luminosity decay potentially over weeks or months. Derived luminosities for 4XJ1751-2759 range up to $\sim10^{35} \text{\,erg s}^{-1}$ at 8\,kpc at the Galactic centre, but neutral hydrogen column densities are greater than predicted Galactic values possibly implying a greater distance to the source, still within our galaxy, further increasing its luminosity. A consideration of optical and IR information in combination with the X-ray observations allow us to exclude the possibility that 4XJ1751-2759 is a star, rotationally powered pulsar or supergiant fast X-ray transient. This rapid, hard, variability is closest to that of outbursts in magnetars than any other known class of X-ray transient.

The MAMMOTH-MOSFIRE program is a deep Keck MOSFIRE K-band spectroscopic follow-up of emission-line galaxies identified in the MAMMOTH-Grism HST WFC3/G141 slitless spectroscopic survey, targeting the core regions of three most massive galaxy protoclusters at cosmic noon. To introduce this program, we present a comprehensive analysis of the emission-line diagnostics for a unique sample of 43 protocluster member galaxies at $z\sim2$, investigating the impact of the overdense environment on their interstellar medium conditions. We characterize their ionization and excitation state using the $\rm [N\,II]\lambda$6584, $\rm [S\,II]\lambda\lambda$6717,6731, and $\rm [O\,I]\lambda$6300 BPT diagrams, from a full suite of rest-frame optical emission lines jointly covered by Keck MOSFIRE and HST G141 spectroscopy. Our analysis reveals a median electron density of $n_{\rm e}\approx290~{\rm cm}^{-3}$ from $\rm [S\,II]$ doublets, consistent with measurements from field galaxies at similar redshifts. Like their field counterparts at $z\sim2$, protocluster galaxies exhibit a systematic offset in the N2 BPT diagram compared to the local star-forming sequence, but no offset in the S2 BPT diagram. Notably, we find significantly enhanced $\rm [O\,I]/H{\alpha}$ ratios, which can be well explained by photoionization models incorporating both $\rm H\,II$ regions and shock excitation. This work highlights the powerful synergy between high-resolution Keck MOSFIRE K-band spectroscopy and HST G141 slitless spectroscopy, enabling comprehensive coverage of the rest-frame optical spectra of galaxies at $z\sim2$.

Aims. Dust enrichment and growth during the initial stages of protoplanetary disk formation were numerically investigated. A particular objective was to determine the effects of various growth barriers, which were mimicked by setting a series of upper permissible limits on maximum dust sizes. Methods. We used the ngFEOSAD code to simulate the three-dimensional dynamics of gas and dust in the polytropic approximation starting from the gravitational collapse of a slowly rotating Bonnor-Ebert sphere to $\approx 12$ kyr after the first hydrostatic core and disk formation. Results. We found that dust growth starts in the contracting cloud in the evolution stage that precedes disk formation and the disk begins to form in an environment that is already enriched in grown dust. The efficiency of dust growth in the disk is limited by dust growth barriers. For dust grains with maximum size < 100 $\mu$m these are likely electrostatic or bouncing barriers, and for larger grains the fragmentation and drift barriers play the major role. The disk midplane becomes quickly enriched with dust, while the vertically integrated distribution of dust shows notable local variations around the canonical 1:100 dust-to-gas mass ratio. These positive and negative deviations are likely caused by local hydrodynamic flows, since the globally integrated dust-to-gas ratio deviates negligibly from the initial 1:100 value. We note that care should be taken when considering models with a fixed dust size, as it may attain a profound negative radial gradient already in the very early stages of disk formation. Models with a constant Stokes number may be preferable in this context. Conclusions. The early dust enrichment and growth may facilitate planet formation as suggested by observations of protoplanetary disk substructures.

We present a dataset of high resolution spectra of the Sun of many strongly polarized lines belonging to the second solar spectrum, i.e. the spectrum near the limb in linear polarization (scattering polarization). These solar spectra were obtained in full Stokes polarimetry (I, Q/I, U/I, V/I) in the quiet Sun at various distances from the limb, and at disk centre for comparison, with the ground based CNRS THEMIS telescope. Polarization rates Q/I up to 7% are obtained in CaI 4227 Å line at $\mu$ = cos$\theta$ = 0, while 2% is reached in SrI 4607 Å line and 1.4% in BaII 4554 Å. The spectra shown here are freely available in FITS format to the research community.

The relationship between quasars and their galaxy environment is important for understanding the evolution of galaxies and supermassive black holes, but it is not fully understood. We perform a wide and deep exploration of the environment of quasars at $0.4 < z < 1.0$ using the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) survey. We investigate the environment of the 1,912 spectroscopically selected quasars from the Sloan Digital Sky Survey (SDSS), using photometrically selected galaxies from the HSC-SSP data, over an area of 505 deg${^{2}}$. The quasar environment is compared to the environment of matched galaxies with similar stellar mass and redshift. We employ the $k$-nearest neighbor method to define the local galaxy number density for both the quasars and the matched galaxies at a scale of a few hundred kpc. As a result, we find that the number density of galaxies around SDSS quasars is lower than that of the matched galaxies by $\sim$11--$20\%$. We also investigate possible correlations between the local galaxy number densities and the quasar properties such as black hole mass and Eddington ratio. As a result, no correlation is found between the local galaxy number densities and these properties of quasars. These results suggest that the quasar activity is not triggered by the high number density of surrounding galaxies at the scale of a few hundred kpc.

Fisher-matrix forecasts are presented for the cosmological surveys of the Javalambre Physics of the Accelerating Universe Astrophysical Survey (J-PAS) and the Subaru Prime Focus Spectrograph (PFS). The wide, low-redshift coverage of J-PAS and the high-density, high-redshift mapping of PFS are strongly complementary: combining the two reduces marginalized uncertainties on all primary parameters compared with either survey individually. Adding the joint J-PAS+PFS data to next-generation CMB measurements from CMB-S4 and \textsc{LiteBird} yields an expected precision of $\sigma(\sum m_\nu)=0.017\,$eV in the $\Lambda$CDM$+\sum m_\nu+N_{\rm eff}$ framework, sufficient to disfavour the inverted neutrino hierarchy at $2.35\,\sigma$ if the true mass sum equals the normal-ordering minimum. Motivated by recent DESI results, we also forecast within a $w_0w_a$CDM$+\sum m_\nu+N_{\rm eff}$ cosmology, adopting the DESI\,DR2 best-fit values ($w_0=-0.758$, $w_a=-0.82$) as fiducial. The combination CMB+J-PAS+PFS then delivers $\sigma(w_0)=0.044$ and $\sigma(w_a)=0.18$, corresponding to a $5.1\,\sigma$ preference for a time-varying dark-energy equation of state. These findings show that J-PAS and PFS, especially when coupled with Stage-IV CMB observations, will provide competitive tests of neutrino physics and the dynamics of cosmic acceleration.

We examine the optical counterparts of the 1829 neutral hydrogen (HI) detections in three pilot fields in the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) using data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys DR10. We find that 17 per cent (315) of the detections are optically low surface brightness galaxies (LSBGs; mean $g$-band surface brightness within 1 $ R_e$ of $> 23$ mag arcsec$^{-2}$) and 3 per cent (55) are optically 'dark'. We find that the gas-rich WALLABY LSBGs have low star formation efficiencies, and have stellar masses spanning five orders of magnitude, which highlights the diversity of properties across our sample. 75 per cent of the LSBGs and all of the dark HI sources had not been catalogued prior to WALLABY. We examine the optically dark sample of the WALLABY pilot survey to verify the fidelity of the catalogue and investigate the implications for the full survey for identifying dark HI sources. We assess the HI detections without optical counterparts and identify 38 which pass further reliability tests. Of these, we find that 13 show signatures of tidal interactions. The remaining 25 detections have no obvious tidal origin, so are candidates for isolated galaxies with high HI masses, but low stellar masses and star-formation rates. Deeper HI and optical follow-up observations are required to verify the true nature of these dark sources.

Whether the current observational data indicate any evidence of interaction between the dark sector is a matter of supreme interest at the present moment. This article searched for an interaction in the dark sector between a pressure-less dark matter and a dark energy fluid with constant equation of state, $w_{\rm DE}$. For this purpose, two non-parametric approaches, namely, the Gaussian Process (GP) and the Artificial Neural Networks (ANN) have been employed and using the Hubble data from Cosmic Chronometers (CC), Pantheon+ from Supernovae Type Ia and their combination we have reconstructed the interaction function. We find that for $w_{\rm DE} =-1$, the interaction in the dark sector is not prominent while for $w_{\rm DE} \neq -1$, evidence of interaction is found depending on the value of $w_{\rm DE}$. In particularly, we find that if we start deviating from $w_{\rm DE} = -1$ either in the quintessence ($w_{\rm DE} > -1$) or phantom ($w_{\rm DE} < -1$) direction, an emergence of dark interaction is observed from both GP and ANN reconstructions. We further note that ANN which is applied for the first time in this context seems to play a very efficient role compared to GP.

The primary epoch of planetary accretion concludes with giant impacts - highly energetic collisions between proto-planets that can play a key role in shaping a planet's inventory of volatile elements. Previous work has shown that single giant impacts have the potential to eject a significant amount of a planet's atmosphere but that the efficiency of atmospheric loss depends strongly on the impact parameters and atmospheric properties. Fully quantifying the role of giant impacts in planetary volatile evolution requires a more complete understanding of the mechanisms driving loss during impacts. Here, we use a suite of 3D smoothed particle hydrodynamics simulations to show that loss in giant impacts is controlled primarily by ejecta plumes near the impact site and breakout of the impact shock in the far field, with the efficiency of the latter well approximated by 1D ground-kick calculations. The relative contributions of each mechanism to loss changes drastically with varying impact parameters. By considering the near and far field separately, we present a scaling law that precisely approximates (to within an average of $\sim$3%) loss from 0.35 to 5.0 Earth mass planets with 5% mass fraction H$_2$-He atmospheres for any combination of impactor mass, impact velocity, and angle. Finally, we apply our scaling law to the results of $N$-body simulations for different solar system formation scenarios. We find that while individual impacts rarely cause significant loss ($>$10%) from roughly Earth-mass planets with such massive primary atmospheres, the cumulative effect of multiple impacts can be substantial (40-70% loss).

Aluminium abundances of B-type stars were spectroscopically determined in order to get information about the galactic gas composition at the time of their formation. For this purpose, two AlII lines at 6243 and 4663A were employed. The non-LTE effect of these AlII lines generally acts in the direction of weakening (i.e., profile becomes shallower) caused by a decrease of line opacity (due to overionization) along with an enhanced line source function (overexcitation), and this effect tends to become progressively larger with an increase in Teff as well as with a decrease in log g (surface gravity). Regarding the AlII 6243 line, while the non-LTE calculation qualitatively reproduces its overall behavior (e.g., transition from absorption to emission at early B-type), some Teff-dependent systematic trend remains unremoved in the non-LTE abundances of normal stars, which means that non-LTE corrections evaluated for this line are quantitatively insufficient. Meanwhile, for the case of the Al II 4663 line, which is more advantageous than the 6243 line in the sense that it is stronger without showing any emission, the resulting non-LTE abundances of ordinary B stars are almost constant at the solar abundance (A~6.5) over the wide Teff range (~10000-20000K), suggesting that the abundances derived from this line are successfully non-LTE-corrected and trustable. Therefore, according to the results from the AlII 4663 line, we may conclude that the Al abundance of the galactic gas in the recent past (several times ~10^7-10^8 yr ago) is almost consistent with the solar composition. As to the Al abundances of HgMn stars (Teff<15000K), our analysis confirmed that this element is conspicuously deficient (by ~0.5-2 dex in comparison with the Sun) in the photosphere of these chemically peculiar stars, as already reported in previous studies.

The von Zeipel-Lidov-Kozai (ZLK) mechanism with tidal friction has been demonstrated as a promising avenue to generate hot Jupiters in stellar binary systems. Previous population studies of hot Jupiter formation have largely examined this mechanism in systems comprised of three bodies: two stars and one planet. However, because stars in a binary system form in similar environments with comparable metallicities, the formation of a single hot Jupiter in such a system may imply that the conditions are more likely met for the companion star, as well. We investigate the ZLK mechanism with tidal friction as a potential mechanism to produce double hot Jupiter systems in stellar binaries. Using N-body simulations, we characterize the evolution of two cold Jupiters, each orbiting one star in a binary system, undergoing mirrored ZLK migration. We then examine the robustness of this mechanism to asymmetries in stellar masses, planet masses, and planet orbital inclinations relative to the binary plane. We predict that, under the assumptions that (1) most hot Jupiters in binary star systems form through ZLK migration of primordially formed cold Jupiters and (2) if one star in a binary system forms a cold Jupiter, the second does as well, a comprehensive search could identify double hot Jupiters in up to ~9% of the close- to moderate- separation a<2000 AU) binary systems that already host a known hot Jupiter. We also argue that a blind search for ZLK-migrated double hot Jupiters should prioritize twin stellar binaries with pericenter approaches of a few hundred AU.

We present improved collision support for TRACE, a state-of-the-art hybrid integrator in REBOUND. TRACE now supports collisional fragmentation and can handle both removing and adding particles mid-timestep. We describe the back-end logic implemented for robust collision support, and compare TRACE's performance to other integrators including MERCURIUS on a large-N protoplanetary disk simulation with various collision prescriptions, a system which TRACE previously could not handle. TRACE matches the behavior of these integrators, while offering potentially vast speedups of over 70x. All updates described in this Note are available with the most recent public release of REBOUND.

HD 209458 b is the first exoplanet on which an atmosphere was detected. Since then, its atmosphere has been investigated using multiple telescopes and instruments. However, many of its atmospheric constraints remain debatable. While HST observations suggested a highly sub-solar metallicity, recent JWST NIRCam observations by Xue et al. 2024 constrained a super-solar metallicity with highly sub-solar C/O. In this work, we show a detailed investigation of HD 209458 b transmission spectra observations from JWST and HST using SANSAR, a newly developed planetary atmosphere modeling framework, with free, equilibrium chemistry and self-consistent grid retrievals. The overall best-fitting model with free retrievals ($\chi^2_{\rm{red}}$=1.21) constrains its metallicity and C/O to be highly sub-solar, while equilibrium chemistry and grid retrievals ($\chi^2_{\rm{red}}$=1.27 and 1.30, respectively) are consistent with solar values using STIS+WFC3+NIRCam observations. The retrieved abundances of H$_2$O and CO$_2$ are almost three orders of magnitude lower (highly sub-solar) with STIS+WFC3+NIRCam compared to just NIRCam, using free retrievals. NIRCam observations alone also result in misleading constraints on metallicity and C/O, with equilibrium chemistry and grid retrieval. We find that the model choice of varying C/H or O/H to vary the C/O in equilibrium chemistry retrievals leads to different metallicity constraints with NIRCam, but similar constraints with STIS+WFC3+NIRCam. We conclude that NIRCam observations alone can lead to overestimation of abundances for exoplanet atmospheres and, therefore, should be used in combination with UV/Optical and near-infrared observations to obtain robust constraints on abundances, C/O, and metallicity. Specifically, even though we can detect the CO$_2$ feature with just NIRCam, we cannot constrain its abundances robustly without the optical baseline.

PSR J0901$-$4046, a likely radio-loud neutron star with a period of 75.88 seconds, challenges conventional models of neutron star radio emission. Here, we showcase results from 46 hours of follow-up observations of PSR J0901$-$4046 using the MeerKAT, Murriyang, GMRT, and MWA radio telescopes. We demonstrate the intriguing stability of the source's timing solution over more than three years, leading to an RMS arrival-time uncertainty of just $\sim$10$^{-4}$ of the rotation period. Furthermore, non-detection below 500 MHz may indicate a low-frequency turnover in the source's spectrum, while no secular decline in the flux density of the source over time, as was apparent from previous observations, has been observed. Using high time-resolution MeerKAT data, we demonstrate two distinct quasi-periodic oscillation modes present in single pulses, with characteristic time scales of 73 ms and 21 ms. We also observe a statistically significant change in the relative prevalence of distinct pulse morphologies compared to previous observations, possibly indicating a shift in the magnetospheric composition over time. Finally, we show that the W$_{50}$ pulse width is nearly constant from 544-4032 MHz, consistent with zero radius-to-frequency mapping. The very short duty cycle ($\sim$1.4$^{\circ}$) is more similar to radio pulsars with periods $>$5 seconds than to radio-loud magnetars. This, along with the lack of magnetar-like outbursts or timing glitches, complicates the identification of the source with ultra-long period magnetar models.

Zeeman-Doppler imaging (ZDI) is used to study the surface magnetic field topology of stars, based on high-resolution spectropolarimetric time series observations. Multiple ZDI inversions have been conducted for the early B-type star tau Sco, which has been found to exhibit a weak but complex non-dipolar surface magnetic field. The classical ZDI framework suffers from a significant limitation in that it provides little to no reliable uncertainty quantification for the reconstructed magnetic field maps, with essentially all published results being confined to point estimates. To fill this gap, we propose a Bayesian framework for probabilistic ZDI. Here, the proposed framework is demonstrated on tau Sco in the weak-field limit. We propose three distinct statistical models, and use archival ESPaDOnS high-resolution Stokes V observations to carry out the probabilistic magnetic inversion in closed form. The surface magnetic field is parameterised by a high-dimensional spherical-harmonic expansion. By comparing three different prior distributions over the latent variables in the spherical-harmonic decomposition, our results showcase the ZDI sensitivity to various hyperparameters. The mean magnetic field maps are qualitatively similar to previously published point estimates, but analysis of the magnetic energy distribution indicates high uncertainty and higher energy content at low angular degrees l. Our results effectively demonstrate that, for stars in the weak-field regime, reliable uncertainty quantification of recovered magnetic field maps can be obtained in closed form with natural assumptions on the statistical model. Future work will explore extending this framework beyond the weak-field approximation and incorporating prior uncertainty over multiple stellar parameters in more complex magnetic inversion problems.

We have performed an extensive statistical investigation of how interplanetary fast forward shocks affect certain turbulence parameters, namely, the cross-helicity, $\sigma_c$, residual energy, $\sigma_r$, and magnetic helicity, $\sigma_m$. A total of 371 shocks detected by Wind at 1 au and seven shocks by Solar Orbiter at 0.3-0.5 au have been analysed. We explore how the aforementioned turbulence parameters and their variation across the shock depend on shock characteristics including the gas compression ratio, upstream plasma beta, velocity jump and shock angle. In the shock vicinity, fluctuations tend on average to show antisunward imbalance (measured as $\sigma_c>0$ when rectified to the Parker spiral direction), a dominance of magnetic energy ($\sigma_r<0$) and zero $\sigma_m$, all being typical solar wind properties . Antisunward imbalance and equipartition ($\sigma_r \sim0$) in the upstream is increasingly prevalent with increasing shock velocity jump and decreasing upstream beta and shock angle. Shocks with large velocity jumps and gas compression ratios have considerably more balanced ($\sigma_c\sim0$) and more magnetically dominated fluctuations downstream than upstream. From upstream to downstream, we also find that the occurrence of time periods fulfilling strict criteria for Alfvénic fluctuations (AFs) usually decreases, while those meeting the criteria for small-scale flux ropes (SFRs) increases. The occurrence of AF periods peaks for quasi-parallel shocks with large velocity jumps and small upstream beta. The occurrence of SFRs increases with increasing gas compression ratio and upstream beta. The shocks observed by Solar Orbiter below 0.5 au display similar distributions of turbulence parameters and upstream-to-downstream changes to those detected at 1 au. These results are relevant for understanding turbulence and charged-particle acceleration at collisionless shocks.

We report on an observational campaign performed with Swift/XRT on the wind-fed supergiant X-ray binary 4U 1909+07 to investigate the nature of the orbital and superorbital modulation of its X-ray emission. A total of 137 XRT observations have been carried out, summing up to a total effective exposure time of 114 ks and covering a total of 66 orbital and 19 superorbital cycles of the source. The XRT data folded on the orbital period of the source confirmed and improved the previously reported variability in intensity and absorption column density, which can be ascribed to the neutron star accreting from the wind of its B supergiant companion across a fairly circular orbit. The XRT data folded on the superorbital period did not provide evidence of significant variations in either the absorption column density and/or the power-law photon index. This may be due to a significant weakening of the superorbital modulation during the times when the XRT observations were carried out, as confirmed by the BAT dynamic power spectrum. We discuss the implications of these findings within the corotating interaction region model proposed to interpret the superorbital variability in wind-fed supergiant X-ray binaries.

Accurately mapping the mass profiles of low mass dwarf spheroidal (dSph) galaxies allows us to test predictions made by dark matter (DM) models. To date, such analyses have primarily been performed on Milky Way (MW) satellites. Meanwhile, the Andromeda Galaxy (M31) is home to 35 known dwarf galaxies, yet only two have been successfully mass-modeled so far. In order to better understand the nature of dark matter, a more comprehensive study of Local Group dwarfs is necessary. In this study, we have undertaken a dynamical study of two higher-luminosity Andromeda dwarf galaxies: Andromeda VI (And VI) and Andromeda XXIII (And XXIII). We infer an enclosed mass for And VI of M(r < r$_{\rm{h}}$) = (4.9 $\pm$ 1.5) $\times$ 10$^{7}$ M$_{\odot}$, corresponding to a mass-to-light ratio of $[M/L]_{r_{\rm{h}}}$ = (27.1 $\pm$ 8.2) M$_{\odot}$/L$_{\odot}$. We infer an enclosed mass for And XXIII of M(r < r$_{\rm{h}}$) = (3.1 $\pm$ 1.9) $\times$ 10$^{7}$ M$_{\odot}$, corresponding to a mass-to-light ratio of $[M/L]_{\rm{r_{h}}}$ = (90.2 $\pm$ 53.9) M$_{\odot}$/L$_{\odot}$. Using the dynamical Jeans modeling tool, GravSphere, we determine And VI and And XXIII's dark matter density at 150 pc, finding $\rho_{\rm{DM,VI}}$(150 pc) = (1.4 $\pm$ 0.5) $\times$ 10$^{8}$ M$_{\odot}$ kpc$^{-3}$ and $\rho_{\rm{DM,XXIII}}$(150 pc) = 0.5$\substack{+0.4 \\ -0.3} \times$ 10$^{8}$ M$_{\odot}$ kpc$^{-3}$. Our results make And VI the first mass-modeled M31 satellite to fall into the cuspy regime, while And XXIII has a lower density, implying either a more cored central dark matter density, or a lowering of the density through tides. This adds And XXIII to a growing list of M31 dwarfs with a central density lower than most MW dwarfs and lower than expected for isolated dwarfs in the Standard Cosmology. This could be explained by the M31 dwarfs having experienced stronger tides than their Milky Way counterparts.

In the standard 2D model of eruption, the eruption of a magnetic flux rope is associated with magnetic reconnection occurring beneath it. However, in 3D, additional reconnection geometries are possible, in particular the AR-RF, where external reconnection involving the overlying arcades (A) and erupting flux rope (R) turns into another arcade and a flare loop (F). This process results in the drifting of the legs of the erupting flux rope. We investigated spectroscopic signatures of such AR-RF reconnection occurring in an erupting filament reconnecting with coronal arcades during a two-ribbon flare. The evolution of the erupting filament eruption is examined using observations by the Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS). As the filament rises into the corona, it reconnects with the surrounding arcade of coronal loops with localized brightenings, resulting in the disappearance of the coronal loops and formation of a hot flux rope, showing slipping motion of its footpoints extending to the previous footpoints of the coronal loops (AR-RF reconnection) as predicted by the 3D extensions to the Standard solar flare model. These brightenings are accompanied by the presence of strong blue-shifts in both the IRIS Si IV and Mg II lines, upto about 200 km/s. The lines are also extremely wide, with non-thermal widths above 100 km/s. Furthermore, a strongly non-Gaussian profile of the most blue-shifted component is detected at the start of the AR-RF reconnection, indicating the presence of accelerated particles and MHD turbulence, and associated with the appearance of hot plasma in the AIA 94 A passband. For the first time, an observation has been reported in which the IRIS slit successfully captures AR-RF reconnection between a filament and overlying arcades, resulting in strong blue-shifts and very broad line profiles.

Dynamical friction is an important phenomena in stellar dynamics resulting in the slowing down of a test particle upon many two-body scatters with background particles. Chandrasekhar's original formulation, developed for idealized infinite and homogeneous systems, has been found to be sufficiently accurate even in models of finite extent and radially dependent density profiles. However, in some cases $N-$body simulations evidenced a breakdown of Chandrasekhar's formalism. In particular, in the case of cored stellar systems, the analytical predictions underestimate the rate of in-fall of the test particle. Several explanations for such discrepancy have been proposed so far, in spite of this it remains unclear whether the origin is a finite N effect or an effect arising from the resonance of the orbits of the test and field particles, which is independent on $N$, such as dynamical buoyancy. Here we aim at shedding some light on this issue with tailored numerical experiments. We perform ad hoc simulations of a massive tracer initially placed on a low eccentricity orbit in spherical equilibrium models with increasing resolution. We use an $N-$body code where the self-consistent interaction among the background particles can be substituted with the effect of the static smooth potential of the system's continuum limit, so that the higher order contributions to the dynamical friction arising from the formation of a wake can be neglected if needed. We find that, contrary to what reported in the previous literature, a suppression of dynamical friction happens in both cuspy and cored models. When neglecting the interaction among field particles we observe in both cases a clear $N^{-1/2}$ scaling of the radius at which dynamical friction ceases to be effective. This hints towards a granularity-induced origin of the so-called core-stalling of the massive tracer in cored models.

From a series of 5 GHz VLBA radio observations taken over 1-yr span, we present the detection of compact highly-polarized radio emission from the T6 brown dwarf WISE J112254.72+255022.2 compatible with electron cyclotron maser emission. Both the total and polarized lightcurves show variability in correspondence with a rotation period of 1.95+/-0.03 hr. Comparison with models indicates that the quasi-steady radio emission of this brown dwarf is produced in circumpolar auroral rings, with remarkable similarity to the main-oval auroras in Jupiter. We have detected a large 100% polarized flare in one of the VLBA epochs (2022.82) which may imply the existence of active longitudes in the auroral rings with a non-axisymmetric beaming cone radiation pattern, similar to the dusk/dawn asymmetries seen in the Jovian radio emissions. We also present a high-precision astrometric analysis of the sky motion of WISE J112254.72+255022.2, resulting in revised values of proper motion and parallax with an improvement in precision of one order of magnitude. The common kinematics of WISE J112254.72+255022.2 with its wide companion, the M-dwarf LHS 302, is confirmed with submilliarcsecond precision, suggesting that this brown dwarf may have formed by gravitational fragmentation of the outer part of a protostellar disc around LHS 302. The astrometric analysis imposes very tight bounds to the presence of low-mass companions around WISE J112254.72+255022.2, ruling out objects more massive than Saturn. Our results strengthen the analogy between radio emitting brown dwarfs and the magnetized planets of our solar system.

Dwarf galaxies serve as powerful laboratories for investigating the underlying physics of galaxy evolution including the impact of baryonic feedback processes and environmental influences. We compare the visual and structural properties of dwarf galaxies in ultra-deep HSC-SSP imaging of the COSMOS field with those measured from realistic HSC-like synthetic observations of dwarfs generated by the Illustris TNG50 and NewHorizon simulations. Using Sérsic profile fitting and non-parametric morphological metrics (Gini, $M_{20}$, asymmetry, and concentration), we evaluate the diversity of structural properties in observed and simulated galaxies. Our analysis shows that NewHorizon and TNG50 galaxies lie at opposite extremes of observed structural trends: NewHorizon produces diffuse, extended galaxies with shallow Sérsic indices, while TNG50 yields compact, concentrated systems with steep indices. Both simulations reproduce observed structural trends more closely at higher stellar masses ($M_{\star}\sim10^{9.5} {\rm M_{\odot}}$) but fail to capture the full diversity of COSMOS dwarfs at lower masses. Non-parametric metrics further show that NewHorizon galaxies exhibit more uneven, clumpy light distributions while TNG50 galaxies have smoother but excessively concentrated profiles. These structural differences reflect underlying differences in their physical prescriptions and are likely driven by differing approaches to ISM physics, supernova feedback and star formation in addition to differences in numerical resolution. Our findings highlight the unique power of low-mass galaxies to constrain differences in simulation physics, especially star formation and feedback. Upcoming surveys from facilities like the Vera C. Rubin Observatory and Euclid will enable more rigorous comparisons with simulations, offering deeper insights into the physical processes shaping galaxy evolution.

One of the main theories for heating of the solar corona is based on the idea that solar convection shuffles and tangles magnetic field lines to make many small-scale current sheets that, via reconnection, heat coronal loops. Tiwari et al 2017 present evidence that, besides depending on loop length and other factors, the brightness of a coronal loop depends on the field strength in the loop feet and the freedom of convection in the feet. While it is known that strong solar magnetic fields suppress convection, the decrease in the speed of horizontal advection of magnetic flux with increasing field strength has not been quantified before. We quantify that trend by analyzing 24hours of HMI SHARP vector magnetograms of each of six sunspot active regions and their surroundings. Using Fourier Local Correlation Tracking, we estimate the horizontal advection speed of the magnetic flux at each pixel in which the vertical component of the magnetic field strength (Bz) is well above (greater than or equal to 150 G) noise level. We find that the average horizontal advection speed of magnetic flux steadily decreases as Bz increases, from 110 pm 3 meters per sec for 150 G (in network and plage) to 10 pm 4 meters per sec for 2500 G (in sunspot umbra). The trend is well fit by a fourth degree polynomial. These results quantitatively confirm the expectation that magnetic flux advection is suppressed by increasing magnetic field strength. The presented quantitative relation should be useful for future MHD simulations of coronal heating.

Context. Several instances of low frequency Quasi-Periodic Oscillations (QPOs) have been reported in ultraluminous X-ray sources (ULXs), including three in pulsating ones (PULXs) to date. The nature of many ULXs is still unclear, as are the detailed properties of accretion in PULXs. Aims. We seek an answer to questions such as: Is there a QPO model that fits the data? Can mHz QPOs be used to constrain the magnetic field and accretion rate of the neutron stars in PULXs? Are all the low frequency QPOs in ULXs a manifestation of the same phenomenon? Methods. We apply Dong Lai's precession model to the PULX data, with the magnetic threading of the accretion disk constrained by recent simulations. Results. Based on the magnetic precession model, and on recent progress in understanding the inner structure of accretion disks, we predict an inverse scaling of QPO frequency with the neutron star period in PULXs. The theoretical curve is largely independent of the stellar magnetic field or mass accretion rate and agrees with the data for the known QPOs in PULXs. The flat-top QPOs detected in ULXs have observational properties that seem to be very different from the QPOs detected in PULXs, indicating they might have a different origin.

Stellar populations serve as a fossil record of galaxy formation and evolution, providing crucial information about the history of star formation and galaxy evolution. The color-magnitude diagram (CMD) stands out as the most accurate tool currently available for inferring the star formation histories (SFHs) of nearby galaxies with stellar-resolved multiband data. The launch of new space telescopes, including JWST, EUCLID, and the upcoming CSST and Roman, will significantly increase the number of stellar-resolved galaxies over the next decade. A user-friendly and customizable CMD fitting package would be valuable for galaxy evolution studies with these data. We develop an open-source Python-based package named \textsc{pancake}, which is fast and accurate in determining SFHs and stellar population parameters in nearby galaxies. We have validated our method via a series of comprehensive tests. First, \textsc{pancake} performs well on mock data, meanwhile the random and systematic uncertainties are quantified. Second, \textsc{pancake} performs well on observational data containing a star cluster and 38 dwarf galaxies (50 fields). Third, the star formation rate (SFR) from \textsc{pancake} is consistent with the SFR from FUV photometry. To ensure compatibility and accuracy, we have included isochrone libraries generated using PARSEC for most of the optical and near-infrared filters used in space telescopes such as HST, JWST, and the upcoming CSST.

Cosmic strings are predicted in many extensions of the Standard Model and constitute a plausible source of gravitational waves (GWs) from the early Universe. In a previous article [1], we pointed out that the GW spectrum from a population of string loops in the scaling regime can exhibit a sharp cutoff frequency associated with the fundamental oscillation mode of string loops. In this paper, we study the effect of particle decay due to kink-kink collisions and cusps on the GW spectrum in the nonscaling scenario introduced in Ref. [2]. We find analytical conditions for the existence of a cutoff frequency in the fundamental spectrum and provide expressions for this frequency. In large regions of parameter space, our results in the nonscaling model turn out to be identical to those in the scaling model. Finally, we demonstrate how the spectrum changes when transitioning from the regime with a cutoff frequency to the regime without a cutoff frequency. Our analytical estimates are validated at qualitatively different benchmark points by comparing them with numerical spectra.

Fast Radio Bursts (FRBs) exhibit scintillation and scattering, often attributed to interactions with plasma screens in the Milky Way and the host galaxy. When these two screens appear "point-like" to each other, two scales of scintillation can be observed with sufficient frequency resolution. A screen perceives a second screen as extended or resolved when the angular size of the latter is smaller than the angular resolution of the former. We define the ratio of these two as the Resolution Power (RP). Previous observational studies have argued that, in the resolving regime, scintillations disappear, assuming that a screen resolving another screen is equivalent to a screen resolving an incoherent emission region. In this theoretical and simulation-based study of resolving effects in two-screen scenarios, we argue that resolving quenches only the relatively broad-scale scintillation and that this quenching is a gradual process. We present qualitative and quantitative predictions for dynamic spectra, spectral autocorrelation functions (ACF), and modulation indices in resolved and unresolved regimes of two-screen systems. We show that the spectral ACF of a two-screen system has a product term in addition to the sum of individual screen contributions, causing the total modulation index to rise to \sqrt(3) in the unresolved regime. To aid in discovering resolving systems, we also present observable trends in multi-frequency observations of a screen resolving another screen or incoherent emission. Additionally we introduce a new formula to estimate the distance between the FRB and the screen in its host galaxy. We also show that this formula, like previous ones in the literature, is only applicable to screens that are two-dimensional in the plane of the sky.

Our velocity with respect to the cosmic frame of rest leads to a dipole in the number count distribution of galaxies. The dipole depends on the source spectrum, which is usually assumed to be a power law, $S(\nu) \propto \nu^{-\alpha}$ and on the flux dependence of the number density of sources. The latter is also generally assumed to be a power law, parametrised with exponent $x$. The velocity can be extracted from the observed dipole once the two parameters $x$ and $\alpha$ are known. The standard procedure uses the mean value of $\alpha$ across the entire sample, and the parameter $x$ is inferred by fitting the cumulative number count, $\frac{dN}{d\Omega}(>S_*) \propto S_*^{-x}$, near the flux limit $S_*$ of the survey. Here, we introduce a simulation procedure to extract the velocity which directly uses the $\alpha$ values of each source rather than their mean and does not rely on the functional form of the cumulative number count near the flux limit. We apply this to the quasar sample in CatWISE2020 data and find that the final results differ from the standard procedure by approximately one sigma.

We investigate the properties of fermion-boson stars (FBSs), which can be viewed as neutron stars with a bosonic dark matter (DM) admixture. A challenge in studying the impact of DM on neutron stars is the absence of a universally accepted nuclear-matter equation of state (EOS), making it difficult to distinguish between the effects of DM and various EOS models. To address this issue, we extend the study of the I-Love-Q universal relations of neutron stars to FBSs with a nonrotating bosonic component by solving the Einstein-Klein-Gordon system. We study how DM parameters, such as the boson particle mass and self-interaction strength, would affect the structure of FBSs and explore the parameter space that leads to deviations from the I-Love-Q relations. The properties of FBSs and the level of deviations in general depend sensitively on the DM parameters. For boson particle mass within the range of $\mathcal{O}(10^{-10} \ \mathrm{eV})$, where the Compton wavelength is comparable to the Schwarzschild radius of a $1 M_\odot$ star, the deviation is up to about 5% level if the star contains a few percent of DM admixture. The deviation increases significantly with a higher amount of DM. We also find that the universal relations are still valid to within a 1% deviation level for boson particle mass $m_b \geq 26.8\times10^{-10} \ \mathrm{eV}$. This effectively sets an upper bound on the boson particle mass, beyond which it becomes not feasible to probe the properties of FBSs by investigating the I-Love-Q relation violations.

We present ultraviolet (UV) through near-infrared (NIR) photometric and spectroscopic observations of the nearby SN 2024pxl, the third Type Ia supernova (SN Ia) in NGC 6384. SN 2024pxl is a Type Iax supernova (SN Iax) with an intermediate luminosity ($M_r = -16.99\pm0.32$ mag) and an average SN Iax light curve decline rate. SN 2024pxl was discovered $\sim$3 days after first light, and the rising light curve follows a single power law that is inconsistent with significant interaction with a companion star or circumstellar material. Our extensive NIR photometric coverage is comparable to that of the well-observed SNe Iax 2005hk and 2012Z, and we demonstrate that the $J-H$ colors of SNe Iax differ from normal SNe Ia and appear to be more homogeneous as a class. Spectroscopically, we report the earliest-ever NIR spectrum of a SN Iax as measured from maximum light ($t\approx-9$ days): a featureless continuum with similarities to a $\sim$9,000 K blackbody, and the line velocities are consistent with a mixed-ejecta structure, with C, Si, and Fe having similar velocities and velocity evolutions. We find a tentative correlation between the $H$-band break Co II velocity $\sim$20 days post-peak and absolute magnitude, with more luminous SNe Iax showing faster Co II velocities. Our observations suggest that SN 2024pxl resulted from the thermonuclear disruption of a CO white dwarf star that undergoes deflagration burning.

We investigate the complementary information to be gained from inflationary gravitational wave (IGW) signals and searches for QCD axion dark matter. We focus on post-inflationary Peccei-Quinn (PQ) breaking axion models that are cosmologically safe. Recent work has shown that a greater number of such models exist. This is because the heavy quarks required for the colour anomaly can provoke a period of heavy quark domination (HQD), which, through decay, dilutes the axion abundance. In this work we show for the first time that the axion dark matter mass can be as low as $m_a\sim10^{-8}\,{\rm eV}$ for models where the heavy quarks decay via dimension 6 terms. This is achieved by allowing the mass of the heavy quarks to differ from the axion decay constant, $m_Q\neq f_a$. Consequently, the observables that would distinguish between pre- and post-inflationary PQ breaking, $m_a$ and the additional relativistic degrees of freedom $\Delta N_{\rm eff}$, now become indiscernible. To solve this, we propose using blue-tilted IGWs to probe HQD. By leveraging the features of the GW signal, future interferometers can probe $m_Q$ and $f_a$ complementing the sensitivity of haloscope experiments, potentially pinning down all relevant parameter that describe the physics. Specifically, we find that BBO and ET GW detectors will both be able to optimistically probe $f_a\gtrsim 10^{14}\,{\rm GeV}$.

We investigate the implications of recent CMB observations for Higgs-Starobinsky inflationary models and their associated reheating dynamics, utilizing data from ACT DR6, Planck 2018, BICEP/Keck 2018, and DESI, collectively referred to as P-ACT-LB-BK18. In addition to direct CMB constraints, we incorporate indirect bounds arising from the potential overproduction of primordial gravitational waves (PGWs), particularly through limits on the effective number of relativistic species, $\Delta N_{\rm eff}$, during Big Bang Nucleosynthesis (BBN). These constraints become especially relevant in scenarios featuring a stiff post-inflationary equation of state $w_{\rm RH}\geq 0.58$. Our analysis shows that, when both P-ACT-LB-BK18 data and $\Delta N_{\rm eff}$ bounds are considered, the viable number of inflationary e-folds is restricted to the range ($57.9$-$62.2$) at the $2\sigma$ confidence level (C.L.). Correspondingly, the reheating temperature is constrained to lie between the BBN energy scale and $10^{12}$ GeV, with the post-inflationary equation-of-state parameter satisfying $w_{\rm RH} > 0.41$. However, no parameter space remains viable at the $1\sigma$ C.L. once $\Delta N_{\rm eff}$ constraints from PGWs are included, rendering the Higgs-Starobinsky model highly restricted.

We study the stability of a hot saturated gas coexisting with condensed particles in an optically thin medium. Such a situation may obtain downstream of a shock, at condensation fronts, or in vaporizing impacts. We show that the gas-particle mixture is subject to a thermal instability whereby a region of lower temperature and higher condensate density cools faster to condense faster. If the region of runaway condensation has a sound-crossing time shorter than its cooling time, then it accretes more mass, in gas and particles, from its higher pressure surroundings. Numerical integration of the linearized perturbation equations demonstrates that this radiation-condensation instability can create particle clumps and voids out of a secularly cooling gas. Provided radiation can escape to cool particle overdensities, thermal instability can help assemble chondrite parent bodies out of the vaporized debris of asteroid collisions, and form planetesimals generally.

We analyze 15 years of Fermi-LAT data and produce a detailed model of the Sun's inverse-Compton scattering emission (solar halo), which is powered by interactions between ambient cosmic-ray electrons and positrons with sunlight. By developing a novel analysis method to analyze moving sources, we robustly detect the solar halo at energies between 31.6 MeV and 100 GeV, and angular extensions up to 45$^\circ$ from the Sun, providing new insight into spatial regions where there are no direct measurements of the galactic cosmic-ray flux. The large statistical significance of our signal allows us to sub-divide the data and provide the first $\gamma$-ray probes into the time-variation and azimuthal asymmetry of the solar modulation potential, finding time-dependent changes in solar modulation both parallel and perpendicular to the ecliptic plane. Our results are consistent with (but with independent uncertainties from) local cosmic-ray measurements, unlocking new probes into both astrophysical and beyond-standard-model processes near the solar surface.

Satellite imagery is increasingly used to complement traditional data collection approaches such as surveys and censuses across scientific disciplines. However, we ask: Do all places on earth benefit equally from this new wealth of information? In this study, we investigate coverage bias of major satellite constellations that provide optical satellite imagery with a ground sampling distance below 10 meters, evaluating both the future on-demand tasking opportunities as well as the availability of historic images across the globe. Specifically, forward-looking, we estimate how often different places are revisited during a window of 30 days based on the satellites' orbital paths, thus investigating potential coverage biases caused by physical factors. We find that locations farther away from the equator are generally revisited more frequently by the constellations under study. Backward-looking, we show that historic satellite image availability -- based on metadata collected from major satellite imagery providers -- is influenced by socio-economic factors on the ground: less developed, less populated places have less satellite images available. Furthermore, in three small case studies on recent conflict regions in this world, namely Gaza, Sudan and Ukraine, we show that also geopolitical events play an important role in satellite image availability, hinting at underlying business model decisions. These insights lay bare that the digital dividend yielded by satellite imagery is not equally distributed across our planet.

Many inverse problems in nuclear fusion and high-energy astrophysics research, such as the optimization of tokamak reactor geometries or the inference of black hole parameters from interferometric images, necessitate high-dimensional parameter scans and large ensembles of simulations to be performed. Such inverse problems typically involve large uncertainties, both in the measurement parameters being inverted and in the underlying physics models themselves. Monte Carlo sampling, when combined with modern non-linear dimensionality reduction techniques such as autoencoders and manifold learning, can be used to reduce the size of the parameter spaces considerably. However, there is no guarantee that the resulting combinations of parameters will be physically valid, or even mathematically consistent. In this position paper, we advocate adopting a hybrid approach that leverages our recent advances in the development of formal verification methods for numerical algorithms, with the goal of constructing parameter space restrictions with provable mathematical and physical correctness properties, whilst nevertheless respecting both experimental uncertainties and uncertainties in the underlying physical processes.

We consider neutrinos scattering off Milky Way dark matter and the impact of this scattering on supernovae neutrinos. This can take the form of attenuation on the initial flux of neutrinos and a time-delayed flux of scattered neutrinos. Considering dark matter masses above 100 MeV and past Milky Way supernovae, we find this time-delayed flux is nearly constant in time. We call this flux the Dark Matter Diffused Supernova Neutrino Background (DMDSNB), and use Super-K limits on the Diffuse Supernova Neutrino Background (DSNB) flux to set limits on the dark matter-neutrino scattering cross section. We find $\sigma_{\rm DM-\nu}/m_{\rm DM} \lesssim 2.4 \times 10^{-24} \mathrm{cm^2}$/GeV for $m_{\rm DM} \gtrsim 1$ GeV, which is the strongest bound to date on dark matter-neutrino scatterings at MeV energies, and stronger than bounds set from SN1987A neutrino attenuation by an order of magnitude. We end by discussing how the DMDSNB could be distinguished from the DSNB.

Instabilities in collective neutrino oscillations can lead to sizeable flavor conversion with vital astrophysical consequences. While it is now recognized that the initial phase space distributions of the different flavors determine the existence and character of instabilities, a rigorous instability condition for generic distributions -- that depend on both energy and emission angles -- is lacking. In this work we identify, analyze, and explain the conditions that are sufficient (and necessary) for a generic collective neutrino flavor instability.

This article investigates the averaging of a scalar degree of freedom that couples universally to matter. It quantifies the approximation of smoothing the matter distribution before solving the Klein--Gordon equation. In the case of Yukawa theories, which enjoy a linear Klein--Gordon equation, the averaging commutes with the field equation as one might expect. While all small-scale distributions of matter lead to field distributions with the same mean, the latter can have different energy densities and pressures when the Compton wavelength of the field is smaller than the smoothing scale. In the non-linear case, such as chameleon theories, this study quantifies the error made by averaging the matter distribution before solving the Klein--Gordon equation. While field fluctuations can become arbitrarily large when the matter source is screened, the commutativity property of linear theories is recovered in the unscreened regime. Implications for cosmology -- and in particular the equation of state in extended quintessence models -- and for laboratory experiments in low density medium are discussed. This analysis, although based on a simplifying description, sheds light on the effects of the small-scale distribution of matter as well as on the care required to define their equation of state and their cosmological signature.

This paper develops a renormalized perturbation theory framework for nonlinear structure formation in a broad class of modified gravity models that exhibit Vainshtein screening, with a focus on a viable subclass of Horndeski theories. We extend earlier perturbative methods, originally applied to DGP model, to construct a self-consistent treatment that captures both the linear modifications to gravity at large scales and the nonlinear screening effects at small scales. In the framework, the response of the gravitational potential to matter density fluctuations is characterized by renormalized propagators, leading to the definition of a nonlinear (or renormalized) effective gravitational constant. The paper details several numerical strategies to compute this renormalized gravitational constant. Numerical examples illustrate how the effective gravitational constant evolves with scale and redshift. These results are key to accurately predicting cosmological observables such as the matter power spectrum and bispectrum in modified gravity scenarios.

We find a new family of galactic metrics corresponding to flat rotation curves at the outer radii. These are vacuum solutions to a gravity theory where the Newton's coupling varies mildly in space. The effective `mass', whose origin is purely geometric, receives a negative non-baryonic contribution. The angle of deflection of a light ray propagating in this geometry is found to be diminished rather than enhanced compared to the Einsteinian bending, the effect being highly suppressed though. Hence, these spacetimes are observationally dintinguishable from other geometric or `dark matter' based alternatives invoked to explain mass discrepancies in galaxies.

We construct a static, spherically symmetric black hole (BH) solution embedded within a dark matter (DM) halo, formulated as a non-vacuum extension of the Schwarzschild spacetime. The DM distribution is modeled via an empirical density profile calibrated to observations of the elliptical galaxy NGC 4649 (M60), incorporating Hubble Space Telescope (HST) imaging, stellar velocity dispersion data, and globular cluster dynamics. The resultant spacetime metric depends on three independent parameters: the black hole mass $M$, the asymptotic circular velocity $V_c$, and the halo scale radius $a$, and smoothly reduces to the Schwarzschild limit as $V_c \to 0$ and $a \to 0$. We analyze the influence of the halo on key geometric and physical quantities, including the event horizon radius, photon sphere, shadow size, and curvature invariants. The Kretschmann scalar exhibits an enhanced sensitivity to halo-induced modifications, particularly in the near-horizon regime. Thermodynamic properties of the solution are also examined. In the extremal limit, characterized by a vanishing surface gravity, the model supports a finite tangential pressure, implying a non-trivial extension of standard black hole thermodynamics. These results highlight the relevance of incorporating astrophysical environments into BH modeling and offer new avenues for testing strong-field gravity through precision observational data.

Regular and spherically symmetric black holes that solve the singularity problems of the Schwarzschild solution are phenomenologically viable at large distance but usually suffer from the Cauchy horizon instability. To overcome this drawback, we extended the analysis to include hyperbolic and toroidal horizon topologies within the framework of static, topologically maximally symmetric spacetimes. We show that both hyperbolic and toroidal black holes can be constructed without Cauchy horizons and without curvature singularities, thereby avoiding the mass inflation instability. These solutions exhibit asymptotic flatness in a generalized quasi-Minkowskian sense. The phenomenological aspects of these solutions are also studied by examining their thermodynamical properties, the photon sphere, and the effective potentials, ensuring consistency with observable properties such as black hole shadows. Lastly, we investigate a reconstruction technique within a scalar-tensor gravity framework, illustrating how the discussed metrics can arise from well-defined scalar field dynamics. Our investigation presents a viable pathway for constructing physically realistic, regular black holes in both General Relativity and modified gravity, broadening the landscape of singularity-free spacetimes and offering models that may better reflect the nature of strong gravitational fields in astrophysical and cosmological settings.

Fibre inflationary models are constructed in type-IIB string flux compactification. These models have been shown to be in agreement with the cosmological observations under appropriate choices of parameters, which originate from their string theory construction. In the present work, we embed such models, originally studied in the cold inflation picture, in the context of warm inflation. We study the viability of different fibre inflation potentials in both strong and weak dissipative regime of warm inflation. In fibre inflation, the inflaton is a four-dimensional complex manifold -- a fibre of a $K3$ fibred Calabi-Yau. The potential in this case is generated by an interplay of various perturbative and non-perturbative corrections. The former type of corrections consists of leading-order $\alpha'^3-$ term, higher derivative $F^4-$ correction, and various string loop corrections of KK, log-loop and winding type. Depending on the balance between several corrections, we present four different fibre inflationary potentials and show that the warm inflationary pictures for all of them can successfully fall in the viable window from both Planck and recent Atacama Cosmology Telescope (ACT) data. We show that warm inflation makes it possible to extend the range of parameters of applicability of these models. Our results also indicate that with the help of a large dissipation ratio, one can achieve a sub-Planckian field excursion, although, this runs on the possibility of moving away from the perturbative control of low-energy four-dimensional supergravity theory.

Applying the holographic 2-flavor Einstein-Maxwell-dilaton model, the parameters of which fixed by lattice QCD, we extract the equations of state for hot quark-gluon plasma around the critical point at $T=182$ MeV, and have corresponding quark star cores constructed. By further adding hadron shells, the mass range of the whole stars spans from $2$ to $17$ solar masses, with the maximum compactness around $0.15$. This result allow them to be black hole mimickers and candidates for gap events. The I-Love-Q-C relations are also analyzed, which show consistency with the neutron star cases when the discontinuity at the quark-hadron interface is not large. Besides, we illustrate the full parameter maps of the energy density and pressure as functions of the temperature and chemical potential, and discuss the constant thermal conductivity case supposing a heat source inside.

We explore the possibility that part of what we call dark matter may be the mark of a preferred frame, revealing a breakdown of diffeomorphism invariance. In the non-relativistic limit this appears as a deviant matter source capable of attracting normal matter, but not feeling the attraction from other forms of matter or from itself. While this implies a violation of momentum conservation, no logical inconsistencies arise in this deviant ``Newtonian'' limit. In contrast, due to Bianchi identities, the relativistic theory must undergo core change, and we discuss a modification of Einstein's gravity capable of coupling a non-conserved source to gravity. It results from fixing some of the spatial components of the metric, thereby constraining the possible diffeomorphisms and clipping some of the equations. Bianchi identities can always be used to refill the equations, but the effective Stueckelberg stresses are so outlandish that this defines symmetry breakdown and violations of local energy-momentum conservation. We work out spherically symmetric solutions with static halos and flat rotation curves, with and without a central black hole. The model has the drawback that it can evade experimental constraints simply by setting to zero the local density of deviant matter (which is a non-dynamic input). Its presence, in contrast, would leave inimitable signatures. We briefly discuss the Hamiltonian formulation of these models, where such dark matter appears as a central charge in the Poisson bracket of the Hamiltonian and the momentum.

In light of recent DAMIC-M results, we present the status of thermal-relic dark matter $\chi$ coupled to a kinetically-mixed dark photon $A^\prime$. In the predictive "direct annihilation" regime, $m_{A'} > m_\chi$, the relic abundance depends on the kinetic mixing parameter, and there is a minimum value compatible with thermal freeze out. Using only electron and nuclear recoil direct detection results, we find that for complex scalar dark matter, the direct-annihilation regime is now excluded for nearly all values of $m_\chi$; the only exception is the resonant annihilation regime where $m_{A'}\approx 2 m_\chi$. Direct annihilation relic targets for other representative models, including Majorana and Pseudo-Dirac candidates, remain viable across a wide range of model parameters, but will be tested with a combination of dedicated accelerator searches in the near future. In the opposite "secluded annihilation" regime, where $m_\chi > m_{A'}$, this scenario is excluded by cosmic microwave background measurements for all $m_\chi \lesssim 30$ GeV. Similar conclusions in both the direct and secluded regimes hold for all anomaly-free vector mediators that couple to the first generation of electrically-charged Standard Model particles.