Papers for Wednesday, Jul 10 2024

The metal content of galaxies is a direct probe of the baryon cycle. A hallmark example is the relationship between a galaxy's stellar mass, star formation rate (SFR), and gas-phase metallicity: the Fundamental Metallicity Relation (FMR). While low-redshift ($z\lesssim4$) observational studies suggest that the FMR is redshift-invariant, recent JWST data indicate deviations from this model. In this study, we utilize the FMR to predict the evolution of the normalisation of the mass-metallicity relation (MZR) using the cosmological simulations Illustris, IllustrisTNG, EAGLE, and SIMBA. Our findings demonstrate that a $z = 0$ calibrated FMR struggles to predict the evolution in the MZR of each simulation. To quantify the divergence of the predictions, we introduce the concepts of a ''static'' FMR, where the role of the SFR in setting the normalization of the MZR does not change with redshift, and a ''dynamic'' FMR, where the role of SFR evolves over time. We find static FMRs in Illustris and SIMBA and dynamic FMRs in IllustrisTNG and EAGLE. We suggest that the differences between these models likely points to the subtle differences in the implementation of the baryon cycle. Moreover, we echo recent JWST results at $z > 4$ by finding significant offsets from the FMR in IllustrisTNG and EAGLE, suggesting that the observed FMR may be dynamic as well. Overall, our findings imply that the current FMR framework neglects important variations in the baryon cycle through cosmic time.

The recent JWST observation of the Firefly Sparkle at $z=8.3$ offers a unique opportunity to link the high- and the low-$z$ Universe. Indeed, the claim of it being a Milky Way (MW) type of assembly at the cosmic dawn opens the possibility of interpreting the observation with locally calibrated galaxy-formation models. Here, we use the MW-evolution model NEFERTITI to perform forward modeling of our Galaxy's progenitors at high-$z$. We build a set of mock spectra for the MW building blocks to make predictions for JWST and to interpret the Firefly Sparkle observation. First, we find that the most massive MW progenitor becomes detectable in a deep survey like JADES from $z\approx 8.2$, meaning that we could have already observed MW-analogs that still need interpretation. Second, we provide predictions for the number of detectable MW progenitors in lensed surveys like CANUCS, and interpret the Firefly Sparkle as a group of MW building blocks. Both the number of detections and the observed NIRCam photometry are consistent with our predictions. By identifying the MW progenitors whose mock photometry best fits the data, we find bursty and extended star-formation histories, lasting $> 150-300$~Myr, and estimate their properties: $M_h \approx 10^{8-9} \, M_{\odot}$, $ M_\star \approx 10^{6.2-7.5}\, M_{\odot}$, $ SFR \approx 0.04-0.20 \, M_{\odot} yr^{-1}$ and $ Z_{gas} \approx 0.04 - 0.24 \, Z_{\odot}$. Uncovering the properties of MW-analogs at cosmic dawn by combining JWST observations and locally-constrained models, will allow us to understand our Galaxy's formation, linking the high- and low-$z$ perspectives.

More than half of all main-sequence (MS) stars have one or more companions, and many of those with initial masses <8 M$_\odot$ are born in hierarchical triples. These systems feature two stars in a close orbit (the inner binary) while a tertiary star orbits them on a wider orbit (the outer binary). In hierarchical triples, three-body dynamics combined with stellar evolution drives interactions and, in many cases, merges the inner binary entirely to create a renovated `Post-Merger Binary' (PMB). By leveraging dynamical simulations and tracking binary interactions, we explore the outcomes of merged triples and investigate whether PMBs preserve signatures of their three-body history. Our findings indicate that in 26-54% of wide double WD binaries (s>100 au), the more massive white dwarf (WD) is a merger product, implying that these DWD binaries were previously triples. Overall, we estimate that $44\pm14\%$ of observed wide DWDs originated in triple star systems and thereby have rich dynamical histories. Additionally, our results suggest that the separations of inner and outer binaries are uncorrelated at birth, providing insights into stellar formation processes. We also examine MS+MS and MS+Red Giant mergers manifesting as Blue Straggler stars (BSSs). These PMBs have orbital configurations and ages similar to most observed BSS binaries. While the triple+merger formation channel can explain the observed chemical abundances, moderate eccentricities, and companion masses in BSS binaries, it likely only accounts for $\sim$20-25% of BSSs. Meanwhile, we predict that the majority of observed single BSSs formed as collisions in triples and harbor long-period (>10 yr) companions. Furthermore, both BSS binaries and DWDs exhibit signatures of WD birth kicks.

Central to model selection is a trade-off between performing a good fit and low model complexity: A model of higher complexity should only be favoured over a simpler model if it provides significantly better fits. In Bayesian terms, this can be achieved by considering the evidence ratio, enabling choices between two competing models. We generalise this concept by constructing Markovian random walks for exploring the entire model spaces governed by the logarithmic evidence ratio, in analogy to the logarithmic likelihood ratio in parameter estimation problems. The theory of Markovian model exploration has an analytical description with partition functions, which we derive for both the canonical and macrocanonical case. We apply our methodology to selecting a polynomial for the dark energy equation of state function $w(a)$ fulfilling sensible physical priors, on the basis of data for the supernova distance-redshift relation. We conclude by commenting on the Jeffrey scale for Bayesian evidence ratios, choices of model priors and derived quantities like Shannon entropies for posterior model probabilities.

The gas in the interstellar medium (ISM) of galaxies is supersonically turbulent. Measurements of turbulence typically rely on cold gas emission lines for low-z galaxies and warm ionized gas observations for z>0 galaxies. Studies of warm gas kinematics at z>0 conclude that the turbulence strongly evolves as a function of redshift, due to the increasing impact of gas accretion and mergers in the early Universe. However, recent findings suggest potential biases in turbulence measurements derived from ionized gas at high-z, impacting our understanding of turbulence origin, ISM physics and disk formation. We investigate the evolution of turbulence using velocity dispersion ($\sigma$) measurements from cold gas tracers (i.e., CO, [CI], [CII]) derived from a sample of 57 galaxy disks spanning the redshift range z=0-5. This sample consists of main-sequence and starburst galaxies with stellar masses $\gtrsim 10^{10} M_{\odot}$. The comparison with current H$\alpha$ kinematic observations and existing models demonstrates that the velocity dispersion inferred from cold gas tracers differ by a factor of $\approx 3$ from those obtained using emission lines tracing warm gas. We show that stellar feedback is the main driver of turbulence measured from cold gas tracers. This is fundamentally different from the conclusions of studies based on warm gas, which had to consider additional turbulence drivers to explain the high values of $\sigma$. We present a model predicting the redshift evolution of turbulence in galaxy disks, attributing the increase of $\sigma$ with redshift to the higher energy injected by supernovae due to the elevated star-formation rate in high-z galaxies. This supernova-driven model suggests that turbulence is lower in galaxies with lower stellar mass compared to those with higher stellar mass. Additionally, it forecasts the evolution of $\sigma$ in Milky-Way like progenitors.

The Extremely Large Telescopes (ELTs), thanks to their large apertures and cutting-edge Multi-Conjugate Adaptive Optics (MCAO) systems, promise to deliver sharper and deeper data even than the JWST. SHARP is a concept study for a near-IR (0.95-2.45 $\mu$m) spectrograph conceived to fully exploit the collecting area and the angular resolution of the upcoming generation of ELTs. In particular, SHARP is designed for the 2nd port of MORFEO@ELT. Composed of a Multi-Object Spectrograph, NEXUS, and a multi-Integral Field Unit, VESPER, MORFEO-SHARP will deliver high angular ($\sim$30 mas) and spectral (R$\simeq$300, 2000, 6000, 17000) resolution, outperforming NIRSpec@JWST (100 mas). SHARP will enable studies of the nearby Universe and the early Universe in unprecedented detail. NEXUS is fed by a configurable slit system deploying up to 30 slits with $\sim$2.4 arcsec length and adjustable width, over a field of about 1.2"$\times$1.2" (35 mas/pix). Each slit is fed by an inversion prism able to rotate by an arbitrary angle the field that can be seen by the slit. VESPER is composed of 12 probes of 1.7"$\times$1.5" each (spaxel 31 mas) probing a field 24"$\times$70". SHARP is conceived to exploit the ELTs apertures reaching the faintest flux and the sharpest angular resolution by joining the sensitivity of NEXUS and the high spatial sampling of VESPER to MORFEO capabilities. This article provides an overview of the scientific design drivers, their solutions, and the resulting optical design of the instrument achieving the required optical performance.

In the host galaxies of radio AGN, kinematically disturbed gas due to jet-driven feedback is a widely observed phenomenon. Simulations predict that the impact of jets on the surrounding gas changes as they grow. Useful insights into this phenomenon can be obtained by characterising radio AGN into different evolutionary stages and studying their impact on gas kinematics. We present a systematic study of the [OIII] gas kinematics for a sample of 5720 radio AGN up to $z\sim0.8$ with a large 1.4 GHz luminosity range of $\approx10^{22.5}-10^{28}$W/Hz, and 1693 [OIII] detections. Taking advantage of the wide frequency coverage of LOFAR and VLA surveys from $144-3000$MHz, we determine the radio spectral shapes, using them to characterise sources into different stages of the radio AGN life cycle. We determine the [OIII] kinematics from SDSS spectra and link it to the life cycle. Our main conclusion is that the [OIII] gas is $\sim$3 times more likely to be disturbed in the peaked spectrum (PS) sources (that represent a young phase of activity) than non-peaked spectrum (NPS) sources (that represent more evolved sources) at $z<0.4$. This changes to a factor of $\sim$2 at $z>0.4$. This shows that on average, the strong impact of jets is limited to the initial stages of the radio AGN life cycle. At later stages, the impact on gas is more gentle. We also determine the dependence of this trend on 1.4GHz and [OIII] luminosities and find that the difference between the two groups increases with 1.4GHz luminosity. Young radio AGN with $L_\mathrm{1.4GHz}>10^{25}$W/Hz have the most extreme impact on [OIII]. Using a stacking analysis, we are further able to trace the changing impact on [OIII] in the high-frequency peaked spectrum (i.e. youngest), low-frequency peaked spectrum ("less young"), and non-peaked spectrum (evolved) radio AGN.

Context: Molecular hydrogen ($\rm{H_2}$) is crucial in galaxy formation and evolution, serving as the main fuel for star formation (SF). In metal-enriched environments, $\rm{H_2}$ primarily forms on interstellar dust grain surfaces. However, due to the complexities of modelling this process, SF in cosmological simulations often relies on empirical or theoretical frameworks validated only in the Local Universe to estimate the abundance of $\rm{H_2}$. Aims: This study aims to model the connection between star, dust, and $\rm{H_2}$ formation processes in cosmological simulations. Methods: We include $\rm{H_2}$ formation on dust grain surfaces and account for molecule destruction and radiation shielding into the SF and feedback model MUPPI. Results: The model reproduces key properties of observed galaxies for stellar, dust, and $\rm{H_2}$ components. The cosmic density of $\rm{H_2}$ ($\rho_{\rm{H2}}$) peaks around $z=1.5$, then decreases by half towards $z=0$, showing milder evolution than observed. The $\rm{H_2}$ mass function since $z=2$ also shows gentler evolution. Our model successfully recovers the integrated molecular Kennicutt-Schmidt (mKS) law between surface star formation rate ($\Sigma_{\rm SFR}$) and surface $\rm{H_2}$ density ($\Sigma_{\rm H2}$) at $z=0$, already evident at $z=2$ with a higher normalization. We find hints of a broken power law with a steeper slope at higher $\Sigma_{\rm H2}$, aligning with some observational findings. Additionally, the $\rm{H_2}$-to-dust mass ratio in galaxies shows a decreasing trend with gas metallicity and stellar mass. The $\rm{H_2}$-to-dust mass fraction for the global galaxy population is higher at higher redshifts. The analysis of the atomic-to-molecular transition on a particle-by-particle basis suggests that gas metallicity cannot reliably substitute the dust-to-gas ratio in models simulating dust-promoted $\rm{H_2}$.

With two directly detected protoplanets, the PDS 70 system is a unique source in which to study the complex interplay between forming planets and their natal environment. The large dust cavity carved by the two giant planets can affect the disk chemistry, and therefore the molecular emission morphology. On the other hand, chemical properties of the gas component of the disk are expected to leave an imprint on the planetary atmospheres. In this work, we reconstruct the emission morphology of a rich inventory of molecular tracers in the PDS 70 disk, and we look for possible chemical signatures of the two actively accreting protoplanets, PDS b and c. We leverage Atacama Large Millimeter/submillimeter Array (ALMA) band 6 high-angular-resolution and deep-sensitivity line emission observations, together with image and $uv$-plane techniques, to boost the detection of faint lines. We robustly detect ring-shaped emission from $^{12}$CO, $^{13}$CO, C$^{18}$O, H$^{13}$CN, HC$^{15}$N, DCN, H$_2$CO, CS, C$_2$H, and H$^{13}$CO$^{+}$ lines in unprecedented detail. Most of the molecular tracers show a peak of the emission inside the millimeter dust peak. We interpret this as the direct impact of the effective irradiation of the cavity wall, as a result of the planet formation process. Moreover, we have found evidence of an O-poor gas reservoir in the outer disk, which is supported by the observations of bright C-rich molecules, the non-detection of SO, and a lower limit on the $\mathrm{CS/SO}$ ratio of $\sim1$. Eventually, we provide the first detection of the c-C$_3$H$_2$ transitions at 218.73 GHz, and the marginal detection of an azimuthal asymmetry in the higher-energy H$_2$CO (3$_{2,1}$-2$_{2,0}$) line, which could be due to accretion heating near PDS 70b.

We obtained New Horizons LORRI images to measure the cosmic optical background (COB) intensity integrated over $0.4\lesssim\lambda\lesssim0.9{~\rm\mu m}.$ The survey comprises 16 high Galactic-latitude fields selected to minimize scattered diffuse Galactic light (DGL) from the Milky Way galaxy, as well as scattered light from bright stars. This work supersedes an earlier analysis based on observations of one of the present fields. Isolating the COB contribution to the raw total sky levels measured in the fields requires subtracting the remaining scattered light from bright stars and galaxies, intensity from faint stars within the fields fainter than the photometric detection-limit, and the DGL foreground. DGL is estimated from Planck HFI $350 {~\rm\mu m}$ and $550 {~\rm\mu m}$ intensities, using a new self-calibrated indicator based on the 16 fields augmented with eight additional DGL calibration fields obtained as part of the survey. The survey yields a highly significant detection ($6.8\sigma$) of the COB at ${\rm 11.16\pm 1.65~(1.47~sys,~0.75~ran) ~nW ~m^{-2} ~sr^{-1}}$ at the LORRI pivot wavelength of 0.608 $\mu$m. The estimated integrated intensity from background galaxies, ${\rm 8.17\pm 1.18 ~nW ~m^{-2} ~sr^{-1}},$ can account for the great majority of this signal. The rest of the COB signal, ${\rm 2.99\pm2.03~ (1.75~sys,~1.03~ran) ~nW ~m^{-2} ~sr^{-1}},$ is formally classified as anomalous intensity but is not significantly different from zero. The simplest interpretation is that the COB is completely due to galaxies.

We present a new method to combine multimass equilibrium dynamical models and pulsar timing data to constrain the mass distribution and remnant populations of Milky Way globular clusters (GCs). We first apply this method to 47 Tuc, a cluster for which there exists an abundance of stellar kinematic data and which is also host to a large population of millisecond pulsars. We demonstrate that the pulsar timing data allow us to place strong constraints on the overall mass distribution and remnant populations even without fitting on stellar kinematics. Our models favor a small population of stellar-mass BHs in this cluster (with a total mass of $412^{+77}_{-146} \mathrm{M_\odot}$), arguing against the need for a large ($ > 2000 \ \mathrm{M_\odot}$) central intermediate-mass black hole. We then apply the method to Terzan 5, a heavily obscured bulge cluster which hosts the largest population of millisecond pulsars of any Milky Way GC and for which the collection of conventional stellar kinematic data is very limited. We improve existing constraints on the mass distribution and structural parameters of this cluster and place stringent constraints on its black hole content, finding an upper limit on the mass in BHs of $\sim 4500 \ \mathrm{M_\odot}$. This method allows us to probe the central dynamics of GCs even in the absence of stellar kinematic data and can be easily applied to other GCs with pulsar timing data, for which datasets will continue to grow with the next generation of radio telescopes.

We present the stellar value-added catalogue based on the Dark Energy Spectroscopic Instrument (DESI) Early Data Release. The catalogue contains radial velocity and stellar parameter measurements for $\simeq$ 400,000 unique stars observed during commissioning and survey validation by DESI. These observations were made under conditions similar to the Milky Way Survey (MWS) currently carried out by DESI but also include multiple specially targeted fields, such as those containing well-studied dwarf galaxies and stellar streams. The majority of observed stars have $16<r<20$ with a median signal-to-noise ratio in the spectra of $\sim$ 20. In the paper, we describe the structure of the catalogue, give an overview of different target classes observed, as well as provide recipes for selecting clean stellar samples. We validate the catalogue using external high-resolution measurements and show that radial velocities, surface gravities, and iron abundances determined by DESI are accurate to 1 km/s, $0.3$ dex and $\sim$ 0.15 dex respectively. We also demonstrate possible uses of the catalogue for chemo-dynamical studies of the Milky Way stellar halo and Draco dwarf spheroidal. The value-added catalogue described in this paper is the very first DESI MWS catalogue. The next DESI data release, expected in less than a year, will add the data from the first year of DESI survey operations and will contain approximately 4 million stars, along with significant processing improvements.

The stellar initial mass function (IMF) is thought to be bottom-heavy in the cores of the most massive galaxies, with an excess of low mass stars compared to the Milky Way. However, studies of the kinematics of quiescent galaxies at 2<z<5 find M/L ratios that are better explained with lighter IMFs. Light IMFs have also been proposed for the unexpected populations of luminous galaxies that JWST has uncovered at z>7, to reduce tensions with galaxy formation models. Here we explore IMFs that are simultaneously bottom-heavy, with a steep slope at low stellar masses, and top-heavy, with a shallow slope at high masses. We derive a form of the IMF for massive galaxies that is consistent with measurements in the local universe and yet produces relatively low M/L ratios at high redshift. This `concordance' IMF has slopes $\gamma_1=2.40\pm0.09$, $\gamma_2=2.00\pm0.14$, and $\gamma_3=1.85\pm0.11$ in the regimes 0.1-0.5 Msun, 0.5-1 Msun, and >1 Msun respectively. The IMF parameter $\alpha$, the mass excess compared to a Milky Way IMF, ranges from $\log(\alpha)\approx+0.3$ for present-day galaxies to $\log(\alpha)\approx-0.1$ for their star forming progenitors. The concordance IMF applies only to the central regions of the most massive galaxies, with velocity dispersions ~300 km/s, and their progenitors. However, it can be generalized using a previously-measured relation between $\alpha$ and $\sigma$. We arrive at the following modification to the Kroupa (2001) IMF for galaxies with $\sigma\gtrsim 160$ km/s: $\gamma_1\approx1.3+4.3\log\sigma_{160}$; $\gamma_2\approx2.3-1.2\log\sigma_{160}$; and $\gamma_3\approx2.3-1.7\log\sigma_{160}$, with $\sigma_{160}=\sigma/160$ km/s. If galaxies grow primarily inside-out, so that velocity dispersions are relatively stable, these relations should also hold at high redshift.

New data from ongoing galaxy surveys, such as the $Euclid$ satellite and the Dark Energy Spectroscopic Instrument (DESI), are expected to unveil physics on the largest scales of our universe. Dramatically affected by cosmic variance, these scales are of interest to large-scale structure studies as they exhibit relevant corrections due to general relativity (GR) in the $n$-point statistics of cosmological random fields. We focus on the relativistic, sample-dependent Doppler contribution to the observed clustering of galaxies, whose detection will further confirm the validity of GR in cosmological regimes. Sample- and scale-dependent, the Doppler term is more likely to be detected via cross-correlation measurements, where it acts as an imaginary correction to the power spectrum of fluctuations in galaxy number counts. We present a method allowing us to exploit multi-tracer benefits from a single data set, by subdividing a galaxy population into two sub-samples, according to galaxies' luminosity/magnitude. To overcome cosmic variance we rely on a multi-tracer approach, and to maximise the detectability of the relativistic Doppler contribution in the data, we optimise sample selection. As a result, we find the optimal split and forecast the relativistic Doppler detection significance for both a DESI-like Bright Galaxy Sample and a $Euclid$-like H$\alpha$ galaxy population.

Galaxy clusters are the most massive, gravitationally-bound structures in the Universe, emerging through hierarchical structure formation of large-scale dark matter and baryon overdensities. Early galaxy ``proto-clusters'' are believed to be important physical drivers of the overall cosmic star-formation rate density and serve as ``hotspots'' for the reionization of the intergalactic medium. Our understanding of the formation of these structures at the earliest cosmic epochs is, however, limited to sparse observations of their galaxy members, or based on phenomenological models and cosmological simulations. Here we report the detection of a massive neutral, atomic hydrogen (HI) gas reservoir permeating a galaxy proto-cluster at redshift $z=5.4$, observed one billion years after the Big Bang. The presence of this cold gas is revealed by strong damped Lyman-$\alpha$ absorption features observed in several background galaxy spectra taken with JWST/NIRSpec in close on-sky projection. While overall the sightlines probe a large range in HI column densities, $N_{\rm HI} = 10^{21.7}-10^{23.5}$ cm$^{-2}$, they are similar across nearby sightlines, demonstrating that they probe the same dense, neutral gas. This observation of a massive, large-scale overdensity of cold neutral gas challenges current large-scale cosmological simulations and has strong implications for the reionization topology of the Universe.

The information gathered from observing planetary systems is not limited to the discovery of planets, but also includes the observational upper limits constraining the presence of any additional planets. Incorporating these upper limits into statistical analyses of individual systems can significantly improve our ability to find hidden planets in these systems by narrowing the parameter space in which to search. Here I include radial velocity (RV), transit, and transit timing variation (TTV) upper limits on additional planets in known multi-planet systems into the DYNAMITE software package and test their impact on the predicted planets for these systems. The tests are run on systems with previous DYNAMITE analysis and with updated known planet parameters in the 2-3 years since the original predictions. I find that the RV limits provide the strongest constraints on additional planets, lowering the likelihood of finding them within orbital periods of ~10-100 days in the inner planetary systems, as well as truncating the likely planet size (radius and/or mass) distributions towards planets smaller than those currently observed. Transit and TTV limits also provide information on the size and inclination distributions of both the known and predicted planets in the system. Utilizing these limits on a wider range of systems in the near future will help determine which systems might be able to host temperate terrestrial planets and contribute to the search for extraterrestrial biosignatures.

Upcoming galaxy surveys aim to map the Universe with unprecedented precision, depth and sky coverage. The galaxy bispectrum is a prime source of information as it allows us to probe primordial non-Gaussianity (PNG), a key factor in differentiating various models of inflation. On the scales where local PNG is strongest, Doppler and other relativistic effects become important and need to be included. We investigate the detectability of relativistic and local PNG contributions in the galaxy bispectrum. We compute the signal-to-noise ratio for the detection of the bispectrum including such effects. Furthermore, we perform information matrix forecasts on the local PNG parameter $f_{\rm NL}$ and on the parametrised amplitudes of the relativistic corrections. Finally, we quantify the bias on the measurement of $f_{\rm NL}$ that arises from neglecting relativistic effects. Our results show that detections of both first- and second-order relativistic effects are promising with forthcoming spectroscopic survey specifications -- and are largely unaffected by the uncertainty in $f_{\rm NL}$. Conversely, we show for the first time that neglecting relativistic corrections in the galaxy bispectrum can lead to $>\!1.5\sigma(f_{\rm NL})$ shift on the detected value of $f_{\rm NL}$, highlighting the importance of including relativistic effects in our modelling.

Microarcsecond resolutions afforded by an optical-NIR array with kilometer-baselines would enable breakthrough science. However significant technology barriers exist in transporting weakly coherent photon states over these distances: primarily photon loss and phase errors. Quantum telescopy, using entangled states to link spatially separated apertures, offers a possible solution to the loss of photons. We report on an initiative launched by NSF NOIRLab in collaboration with the Center for Quantum Networks and Arizona Quantum Initiative at the University of Arizona, Tucson, to explore these concepts further. A brief description of the quantum concepts and a possible technology roadmap towards a quantum-enhanced very long baseline optical-NIR interferometric array is presented. An on-sky demonstration of measuring spatial coherence of photons with apertures linked through the simplest Gottesman protocol over short baselines and with limited phase fluctuations is envisaged as the first step.

We present ~ 126 new spectroscopically identified members of the GD-1 tidal stream obtained with the 5000-fiber Dark Energy Spectroscopic Instrument (DESI). We confirm the existence of a ``cocoon'' which is broad (FWHM~2.932deg~460pc) and kinematically hot (velocity dispersion, sigma~5-8km/s) component that surrounds a narrower (FWHM~0.353deg~55pc) and colder (sigma~ 2.2-2.6km/s) thin stream component (based on a median per star velocity precision of 2.7km/s). The cocoon extends over at least a ~ 20deg segment of the stream observed by DESI. The thin and cocoon components have similar mean values of [Fe/H]: -2.54+/- 0.04dex and -2.45+/-0.06dex suggestive of a common origin. The data are consistent with the following scenarios for the origin of the cocoon. The progenitor of the GD-1 stream was an accreted globular cluster (GC) and: (a) the cocoon was produced by pre-accretion tidal stripping of the GC while it was still inside its parent dwarf galaxy; (b) the cocoon is debris from the parent dwarf galaxy; (c) an initially thin GC tidal stream was heated by impacts from dark subhalos in the Milky Way; (d) an initially thin GC stream was heated by a massive Sagittarius dwarf galaxy; or a combination of some these. In the first two cases the velocity dispersion and mean metallicity are consistent with the parent dwarf galaxy having a halo mass of ~0^9\msun. Future DESI spectroscopy and detailed modeling may enable us to distinguish between these possible origins.

Huang et al. (2024) measured the derivative of the phase $\phi_{\mathrm{w}}$ of the Galactic warp traced by classical Cepheids with respect to their age $\tau$ and interpreted it as the warp precession rate $\omega\equiv\mathrm{d}\phi_{\mathrm{w}}/\mathrm{d}t=-\mathrm{d}\phi_{\mathrm{w}}/\mathrm{d}\tau$. This interpretation is unfounded: young stars follow trajectories close to those of their parental gas and trace the instantaneous gas warp, not its shape at their time of birth: $\phi_{\mathrm{w}}$ should hardly depend on Cepheid age. We show that the measured $\mathrm{d}\phi_{\mathrm{w}}/\mathrm{d}\tau>0$ is consistent with an omitted-variable bias from neglecting the natural twist $\mathrm{d}\phi_{\mathrm{w}}/\mathrm{d}R$ of the warp and the $R$-$\tau$ correlation for Cepheids (originating from the Galactic metallicity gradient and the Cepheid metallicity-age correlation).

We explore an alternative explanation for the low-mass ultra-compact star in the supernova remnant HESS~J1731-347 using a model-agnostic approach to construct hybrid equations of state. The hadronic part of the hybrid equation of state is constructed using a generalized piecewise polytropic scheme, while the quark phase is described by the generic constant speed of sound model. We assume an abrupt first-order hadron-quark phase transition with a slow conversion speed between phases. Our equations of state align with modern Chiral Effective Field Theory calculations near nuclear saturation density and are consistent with perturbative Quantum Chromodynamics calculations at high densities. Using this theoretical framework, we derive a wide range of hybrid equations of state capable of explaining the light compact object in HESS~J1731-347 in a model-independent manner, without fine-tuning. These equations of state are also consistent with modern astronomical constraints from high-mass pulsar timing, NICER observations, and multimessenger astronomy involving gravitational waves. Our results support the hypothesis that the compact object in HESS~J1731-347 could plausibly be a slow stable hybrid star.

Extragalactic fast X-ray transients (FXTs) are short-duration ($\sim$ ks) X-ray flashes of unknown origin, potentially arising from binary neutron star mergers. We investigate the possible link between FXTs and the afterglows of off-axis merger-induced gamma-ray bursts (GRBs). By modelling the broadband afterglows of 13 GRBs, we make predictions for their X-ray light curve behaviour had they been observed off-axis, considering both a uniform jet with core angle $\theta_{C}$ and a Gaussian-structured jet with truncation angle $\theta_{W} = 2\theta_{C}$. We compare their peak X-ray luminosity, duration, and temporal indices with those of the currently known extragalactic FXTs. Our analysis reveals that a slightly off-axis observing angle of $\theta_{\text{obs}}\approx (2.2-3)\theta_{C}$ and a structured jet are required to explain the shallow temporal indices of the FXT light curves. In the case of a structured jet, the durations of the FXTs are consistent with those of the off-axis afterglows for the same range of observing angles, $\theta_{\text{obs}}\approx (2.2-3)\theta_{C}$. While the off-axis peak X-ray luminosities are consistent only for $\theta_{\text{obs}} = 2.2\theta_{C}$, focussing on individual events reveals that the match of all three properties of the FXTs at the same viewing angle is possible in the range $\theta_{\text{obs}} \sim (2.2-2.6)\theta_{C}$. Despite the small sample of GRBs analysed, these results show that there is a region of the parameter space - although quite limited - where the observational properties of off-axis GRB afterglows can be consistent with those of the newly discovered FXTs. Future observations of FXTs discovered by the recently launched Einstein Probe mission and GRB population studies combined with more complex afterglow models will shed light on this possible GRB-FXT connection, and eventually unveil the progenitors of some FXTs.

(Abridged) The Abundance Discrepancy problem in planetary nebulae (PNe) has long puzzled astronomers. NGC6153, with its high Abundance Discrepancy Factor (ADF~10), provides an opportunity to understand the chemical structure and ionisation processes by constructing detailed emission line maps and examining variations in electron temperature and density. We used the MUSE spectrograph to acquire IFU data covering the wavelength range 4600-9300 Å with a spatial sampling of 0.2 arcsec and spectral resolutions ranging from R = 1600-3500. We created emission line maps for 60 lines and two continuum regions. We developed a tailored methodology for the analysis of the data, including correction for recombination contributions to auroral lines and the contributions of different plasma phases. Our analysis confirmed the presence of a low-temperature plasma component in NGC6153. We find that electron temperatures derived from recombination line/continuum diagnostics are significantly lower than those derived from collisionally excited lines diagnostics. Ionic chemical abundance maps were constructed, considering the weight of the cold plasma phase in the HI emission. Adopting this approach, we found ionic abundances that could be up to 0.2 dex lower for those derived from CELs and up to 1.1 dex higher for those derived from RLs than in the case of an homogeneous HI emission. The Abundance Contrast Factor (ACF) between both plasma components was defined, with values, on average, 0.9 dex higher than the ADF. Different methods for calculating ionisation correction factors (ICFs) yielded consistent results. Our findings emphasize that accurate chemical abundance determinations in high-ADF PNe must account for multiple plasma phases.

Diffuse ionized gas pervades the disk of the Milky Way. We detect extremely faint emission from this Galactic Warm Ionized Medium (WIM) using the Green Bank Telescope to make radio recombination line (RRL) observations toward two Milky Way sight lines: G20, $(\ell,{\it b}) = (20^\circ, 0^\circ)$, and G45, $(\ell,{\it b}) = (45^\circ, 0^\circ)$. We stack 18 consecutive Hn$\alpha$ transitions between 4.3-7.1 GHz to derive ${\rm \langle Hn\alpha \rangle}$ spectra that are sensitive to RRL emission from plasmas with emission measures EM >10 ${\rm \,cm^{-6}\,pc}$. Each sight line has two Gaussian shaped spectral components with emission measures that range between $\sim$100 and $\sim$300 ${\rm \,cm^{-6}\,pc}$. Because there is no detectable RRL emission at negative LSR velocities the emitting plasma must be located interior to the Solar orbit. The G20 and G45 emission measures imply RMS densities of 0.15 and 0.18$\,{\rm cm^{-3}}$, respectively, if these sight lines are filled with homogeneous plasma. The observed ${\rm \langle Hn\beta \rangle}$/${\rm \langle Hn\alpha\rangle}$ line ratios are consistent with LTE excitation for the strongest components. The high velocity component of G20 has a narrow line width, 13.5 km s$^{-1}$, that sets an upper limit of <4,000 K for the plasma electron temperature. This is inconsistent with the ansatz of a canonically pervasive, low density, $\sim$ 10,000 K WIM plasma.

We study the rotational properties of inverted hybrid stars (also termed cross stars), which have been recently proposed as a possible new class of compact stars characterized by an outer layer of quark matter and a core of hadrons, in an inverted structure compared to traditional hybrid stars. We analyze distinct models representing varying depths of quark-hadron phase transitions. Our findings reveal that, while cross stars rotating at their Kepler frequencies typically exhibit a significantly higher mass and larger circumferential radius as anticipated, interestingly, there is a significant increase in potential twin configurations in the case of rapid rotations. We further study sequences of constant baryonic mass, representing potential paths of rotational evolution. Our results indicate that not all stars in these sequences are viable due to the onset of phase transitions during spin-down, leading to possible mini-collapses. We also investigate the phenomenon of ``back-bending" during spin-down sequences, which is manifested in a rather different shape for cross stars due to their inverted structure and the large density discontinuity caused by the strong phase transition, in contrast to traditional hybrid stars. Our research enriches existing studies by introducing the significant aspect of rotation, unveiling intr

We are developing an adaptive secondary mirror (ASM) that uses a new actuator technology created by the Netherlands Organization for Applied Scientific Research (TNO). The TNO hybrid variable reluctance actuators have more than an order of magnitude better efficiency over the traditional voice coil actuators that have been used on existing ASMs and show potential for improving the long-term robustness and reliability of ASMs. To demonstrate the performance, operations, and serviceability of TNO's actuators in an observatory, we have developed a 36-actuator prototype ASM for the NASA Infrared Telescope Facility (IRTF) called IRTF-ASM-1. IRTF-ASM-1 provides the first on-sky demonstration of this approach and will help us evaluate the long-term performance and use of this technology in an astronomical facility environment. We present calibration and performance results with the ASM in a Meniscus Hindle Sphere lens setup as well as preliminary on-sky results on IRTF. IRTF-ASM-1 achieved stable closed-loop performance on-sky with H-band Strehl ratios of 35-40% in long-exposure images under a variety of seeing conditions.

1I/`Oumuamua and 2I/Borisov are the first macroscopic interstellar objects to be detected in the solar system. Their discovery has triggered a tsunami of scientific interest regarding the physical properties, dynamics and origin of the so-called interstellar interloper population. While it is clear that a deep understanding of these issues cannot be reached from a sample of just two bodies, the emergence of this new field of astronomical study is particularly fascinating, with ramifications from planetary science to galactic dynamics.

Based on the rate of change of its orbital period, PSR J2043+1711 has a substantial peculiar acceleration of 3.5 $\pm$ 0.8 mm/s/yr, which deviates from the acceleration predicted by equilibrium Milky Way models at a $4\sigma$ level. The magnitude of the peculiar acceleration is too large to be explained by disequilibrium effects of the Milky Way interacting with orbiting dwarf galaxies ($\sim$1 mm/s/yr), and too small to be caused by period variations due to the pulsar being a redback. We identify and examine two plausible causes for the anomalous acceleration: a stellar flyby, and a long-period orbital companion. We identify a main-sequence star in \textit{Gaia} DR3 and Pan-STARRS DR2 with the correct mass, distance, and on-sky position to potentially explain the observed peculiar acceleration. However, the star and the pulsar system have substantially different proper motions, indicating that they are not gravitationally bound. However, it is possible that this is an unrelated star that just happens to be located near J2043+1711 along our line of sight (chance probability of 1.6\%). Therefore, we also constrain possible orbital parameters for a circumbinary companion in a hierarchical triple system with J2043+1711; the changes in the spindown rate of the pulsar are consistent with an outer object that has an orbital period of 80 kyr, a companion mass of 0.3 $M_\odot$ (indicative of a white dwarf or low-mass star), and a semi-major axis of 2000 AU. Continued timing and/or future faint optical observations of J2043+1711 may eventually allow us to differentiate between these scenarios.

The $Roman$ microlensing program can detect and fully characterize black holes (BHs) that are in orbit with about 30 million solar-type and evolved stars with periods up to the mission lifetime $P<T=5$ yr, and semi-major axes $a>0.2$au, i.e., $P> 10$ d $(M/M_\odot)^{-1/2}$, where $M$ is the BH mass. For BH companions of about 150 million later (fainter) main-sequence stars, the threshold of detection is $a>0.2$ au $\times 10^{(H_{\rm Vega}-18.5)/5}$. The present $Roman$ scheduling creates a "blind spot" near periods of $P=3.5$ yr due to a 2.3-year gap in the data. It also compromises the characterization of BHs in eccentric orbits with periods $P>3$ yr and peribothra within a year of the mission midpoint. I show that one can greatly ameliorate these issues by making a small adjustment to the $Roman$ observing schedule. The present schedule aims to optimize proper-motion measurements, but the adjustment proposed here would degrade these by only 4%-9%. For many cases of $P>90$ d BHs, there will be discrete and/or continuous degeneracies. For G-dwarf and evolved sources, it will be straightforward to resolve these by radial-velocity (RV) follow-up observations, but such observations will be more taxing for fainter sources. Many BH-binaries in orbits of 5 yr $<P<10$ yr will be reliably identified as such from the $Roman$ data, but will lack precise orbits. Nevertheless, the full orbital solutions can be recovered by combining $Roman$ astrometry with RV followup observations. BH binaries with periods 10 yr $<P<$ 95 yr $(M/10 M_\odot)^{1/4}$ can be detected from their astrometric acceleration, but massive multi-fiber RV monitoring would be needed to distinguish them from the astrophysical background due to stellar binaries.

While galaxy clusters are dominated by quiescent galaxies at local, they show a wide range in quiescent galaxy fraction (QF) at higher redshifts. Here, we present the discovery of two galaxy clusters at $z \sim 0.95$ with contrasting QFs despite having similar masses (log ($M_{200}/M_{\odot}$)$ \sim 14$) and spectra and redshifts of 29 galaxies in these clusters and 76 galaxies in the surrounding area. The clusters are found in the Ultra Deep Survey (UDS) field and confirmed through multi-object spectroscopic (MOS) observation using the Inamori Magellan Areal Camera and Spectrograph (IMACS) on the Magellan telescope. The two clusters exhibit QFs of $0.094^{+0.11}_{-0.032}$ and $0.38^{+0.14}_{-0.11}$, respectively. Analysis of large-scale structures (LSSs) surrounding these clusters finds that properties of these clusters are consistent with the anti-correlation trend between the QF and the extent of surrounding LSS, found in Lee et al. (2019), which can be interpreted as a result from the replenishment of young, star-forming galaxies keeps the QF low when galaxy clusters are accompanied by rich surrounding environments.

Since solar cycle 16, the { heliospheric} current sheet (HCS) has been found to be shifted southward during the late declining to minimum phase. However, this trend is broken at the end of solar cycle 24. In this paper, we analyze the shift of the HCS by using information obtained from coronal model and insitu data provide by the near-Earth OMNI database and the Parker Solar Probe (PSP). Coronal potential field source surface (PFSS) modeling results show that the northward shift is established at the beginning of 2018 and remains stable for about two years. Interplanetary magnetic field data obtained from and within 1 au also support the northward shift, as the southern polarity T appears more frequently than the northern polarity A between 2018-2020. Both model results and insitu observation obtained by PSP imply that the HCS shift is established in the corona, and then propagates into the heliosphere. The quadrupole term still has a significant influence on the formation of the HCS shift.

A systematic comparison of the models of the circumgalactic medium (CGM) and their observables is crucial to understanding the predictive power of the models and constraining physical processes that affect the thermodynamics of CGM. This paper compares four analytic CGM models: precipitation, isentropic, cooling flow, and baryon pasting models for the hot, volume-filling CGM phase, all assuming hydrostatic or quasi-hydrostatic equilibrium. We show that for fiducial parameters of the CGM of a Milky-Way (MW) like galaxy ($\rm M_{vir} \sim 10^{12}~M_{\odot}$ at $z\sim 0$), the thermodynamic profiles -- entropy, density, temperature, and pressure -- show most significant differences between different models at small ($r\lesssim 30$ kpc) and large scales ($r\gtrsim 100$ kpc) while converging at intermediate scales. The slope of the entropy profile, which is one of the most important differentiators between models, is $\approx 0.8$ for the precipitation and cooling flow models, while it is $\approx0.6$ and 0 for the baryon pasting and isentropic models, respectively. We make predictions for various observational quantities for an MW mass halo for the different models, including the projected Sunyaev-Zeldovich (SZ) effect, soft X-ray emission (0.5--2 keV), dispersion measure, and column densities of oxygen ions (OVI, OVII, and OVIII) observable in absorption.

In this short contribution, we explore the prior dependence of the recent DESI results, according to which a Bayesian comparison of $\Lambda$CDM with $w_0w_a$CDM cosmologies favors dynamical dark energy. It is a simple exercise to show that extending the prior lower bound of the dark energy parameters tilts the preference in favor of $\Lambda$CDM. Adopting the PantheonPlus supernovae catalog, for instance, a shift of the lower bound for $w_0,w_a$ from $-3$ to beyond $-4.6$ and $-5$, respectively, is sufficient to favor $\Lambda$CDM. This calls for caution when interpreting DESI results in the Bayesian context.

The cosmological dispersion measure (DM) as a function of redshift, derived from localized fast radio bursts (FRBs), has been used as a tool for constraining the cosmic ionized fraction and cosmological parameters. For these purposes, the DM in a homogeneous cosmological model has typically been used, neglecting the inhomogeneity of matter distribution. In this study, we derive a bias in the ensemble average of the DM over many FRBs owing to gravitational lensing by the inhomogeneous matter distribution based on cosmological perturbation theory. We demonstrate that the ensemble average is $0.4 \, \%$--$1\,\%$ smaller than the DM in the corresponding homogeneous model for a source redshift of $z_{\rm s}=1$, according to recent cosmological hydrodynamic simulations of IllustrisTNG and BAHAMAS. This reduction occurs because light rays from FRBs tend to avoid high-density regions owing to lensing deflection. We also discuss another selection effect, magnification bias, where demagnified FRBs with low DMs, fainter than the detection threshold, are excluded from the observed sample, leading to a selective observation of magnified FRBs with high DMs. Lensing bias, including magnification bias, must be considered to achieve percent level accuracy in the DM--redshift relation.

Ice mantles play a crucial role in shaping the astrochemical inventory of molecules during star and planet formation. Small-scale molecular processes have a profound impact on large-scale astronomical evolution. The areas of solid-state laboratory astrophysics and computational chemistry study these processes. We review the laboratory effort on ice spectroscopy; methodological advances and challenges; and laboratory and computational studies of ice physics and ice chemistry. The latter we put in context with the ice evolution from clouds to disks. Three takeaway messages from this review are - Laboratory and computational studies allow interpretation of astronomical ice spectra in terms of identification, ice morphology and, local environmental conditions as well as the formation of the involved chemical compounds. - A detailed understanding of the underlying processes is needed to build reliable astrochemical models to make predictions on the abundances in space. - The relative importance of the different ice processes studied in the laboratory and computationally changes along the process of star and planet formation.

Since the first microlensing planet discovery in 2003, more than 200 planets have been detected with gravitational microlensing, in addition to several free-floating planet and black hole candidates. In this chapter the microlensing theory is presented by introducing the numerical methods used to solve binary and triple lens problems and how these lead to the characterisation of the planetary systems. Then the microlensing planetary detection efficiency is discussed, with an emphasis on cold planets beyond the snow line. Furthermore, it will be explained how the planetary characterisation can be facilitated when the microlensing light curves exhibit distortions due to second order effects such as parallax, planetary orbital motion, and extended source. These second order effects can be turned to our advantage, and become useful to ultimately better characterise the planetary systems, but they can also introduce degeneracies in the light curve models. It will be explained how the use of modern observational and computational techniques enables microlensers to solve these degeneracies and estimate the planetary system parameters with very high accuracy. Then a review of the main discoveries to date will be presented while exploring the recent statistical results from high-cadence ground-based surveys and space-based observations, especially on the planet mass function. Finally, future prospects are discussed, with the expected advances from dedicated space missions, extending the planet sensitivity range down to Mars mass.

Exoplanets with masses between Earth and Neptune are amongst the most commonly observed, yet their properties are poorly constrained. Their transmission spectra are often featureless, which indicate either high-altitude clouds or a high atmospheric metallicity. The archetypical warm Neptune GJ 436b is such a planet showing a flat transmission spectrum in observations with the Hubble Space Telescope (HST). Ground-based high-resolution spectroscopy (HRS) effectively probes exoplanet atmospheres at higher altitudes and can therefore be more sensitive to absorption coming from above potential cloud decks. In this paper we aim to investigate this for the exoplanet GJ 436b. We present new CRIRES+ HRS transit data of GJ 436b. Three transits were observed, but since two were during bad weather conditions, only one transit was analyzed. The radiative transfer code petitRADTRANS was used to create atmospheric models for cross-correlation and signal-injection purposes, including absorption from H$_2$O, CH$_4$, and CO. No transmission signals were detected, but atmospheric constraints can be derived. Injection of artificial transmission signals indicate that if GJ 436b would have a cloud deck at pressures P>10 mbar and a <300$\times$ solar metallicity, these CRIRES+ observations should have resulted in a detection. We estimate that the constraints presented here from one ground-based HRS transit are slightly better than those obtained with four HST transits. Combining HRS data from multiple transits is an interesting avenue for future studies of exoplanets with high-altitude clouds.

Grids of stellar evolution models with rotation using the Geneva stellar evolution code (Genec) have been published for a wide range of metallicities. We introduce the last remaining grid of Genec models, with a metallicity of $Z=10^{-5}$. We study the impact of this extremely metal-poor initial composition on various aspects of stellar evolution, and compare it to the results from previous grids at other metallicities. We provide electronic tables that can be used to interpolate between stellar evolution tracks and for population synthesis. Using the same physics as in the previous papers of this series, we computed a grid of stellar evolution models with Genec spanning masses between 1.7 and 500 $M_\odot$, with and without rotation, at a metallicity of $Z=10^{-5}$. Due to the extremely low metallicity of the models, mass-loss processes are negligible for all except the most massive stars. For most properties (such as evolutionary tracks in the Hertzsprung-Russell diagram, lifetimes, and final fates), the present models fit neatly between those previously computed at surrounding metallicities. However, specific to this metallicity is the very large production of primary nitrogen in moderately rotating stars, which is linked to the interplay between the hydrogen- and helium-burning regions. The stars in the present grid are interesting candidates as sources of nitrogen-enrichment in the early Universe. Indeed, they may have formed very early on from material previously enriched by the massive short-lived Population III stars, and as such constitute a very important piece in the puzzle that is the history of the Universe.

In time-domain radio astronomy with arrays, voltages from individual antennas are added together with proper delay and fringe correction to form the beam in real-time. In order to achieve the correct phased addition of antenna voltages one has to also correct for the ionospheric and instrumental gains. Conventionally this is done using observations of a calibrator source located near to the target field. This scheme is sub-optimal since it does not correct for the variation of the gains with time and position in the sky. Further, since the ionospheric phase variation is typically most rapid at the longest baselines, the most distant antennas are often excluded while forming the beam. We present here a different methodology ("in-field phasing"), in which the gains are obtained in real-time using a model of the intensity distribution in the target field, which overcomes all of these drawbacks. We present observations with the upgraded Giant Metrewave Radio Telescope (uGMRT) which demonstrates that in-field phasing does lead to a significant improvement in sensitivity. We also show, using observations of the millisecond pulsar J1120$-$3618 that this in turn leads to a significant improvement of measurements of the Dispersion Measure and Time of Arrival. Finally, we present test observations of the GMRT discovered eclipsing black widow pulsar J1544+4937 showing that in-field phasing leads to improvement in the measurement of the cut-off frequency of the eclipse.

The gamma-ray emitting narrow-line Seyfert 1 galaxies are a unique class of objects that launch powerful jets from relatively lower-mass black hole systems compared to the Blazars. However, the black hole masses estimated from the total flux spectrum suffer from the projection effect, making the mass measurement highly uncertain. The polarized spectrum provides a unique view of the central engine through scattered light. We performed spectro-polarimetric observations of the gamma-ray emitting narrow-line Seyfert 1 galaxy 1H0323+342 using \textit{SPOL/MMT}. The degree of polarization and polarization angle are 0.122 $\pm$ 0.040\% and 142 $\pm$ 9 degrees, while the H$\alpha$ line is polarized at 0.265 $\pm$ 0.280\%. We decomposed the total flux spectrum and estimated broad H$\alpha$ FWHM of 1015 \kms^{-1}. The polarized flux spectrum shows a broadening similar to the total flux spectrum, with a broadening ratio of 1.22. The Monte Carlo radiative transfer code `STOKES' applied to the data provides the best fit for a small viewing angle of 9-24 degrees and a small optical depth ratio between the polar and the equatorial scatters. A thick BLR with significant scale height can explain a similar broadening of the polarized spectrum compared to the total flux spectrum with a small viewing angle.

Active galactic nuclei (AGN) are extremely variable in the X-ray band down to very short time scales. However, the driver of the X-ray variability is still poorly understood. Previous results suggest that the hot corona, which is responsible for the primary Comptonized emission observed in AGN, should have an important role in driving the X-ray variability. In this work, we investigate the connection between the X-ray amplitude variability and the coronal physical parameters, namely the temperature ($kT$) and optical depth ($\tau$). We present the spectral and timing analysis of 46 NuSTAR observations corresponding to a sample of 20 AGN. For each source we derive the coronal temperature and optical depth through X-ray spectroscopy, and we compute the normalized excess variance for different energy bands at a time scale of $10$ ks. We find a strong inverse correlation between $kT$ and $\tau$, with correlation coefficient $r<-0.9$ and negligible null probability. No clear dependence between the temperature and physical properties such as the black hole mass and the Eddington ratio is found. We also find that the observed X-ray variability does not correlate with either the coronal temperature or optical depth under the thermal equilibrium assumption, while it is anti-correlated with the black hole mass. These results can be interpreted in a scenario where one possibility is that the observed X-ray variability could be mainly driven by variations in coronal physical properties on a time scale of less than $10$ ks, whereas we assume thermal equilibrium at such time scales in this paper, given the capability of the currently available hard X-ray telescopes. However, it is also possible that the X-ray variability is mostly driven by the absolute size of the corona, which depends on the supermassive black hole mass, rather than by its physical properties.

We constrain wind parameters of a sample of 18 O-type stars in the LMC, through analysis with stellar atmosphere and wind models including the effects of optically thick clumping. This allows us to determine the most accurate spectroscopic mass-loss and wind structure properties of massive stars at sub-solar metallicity to date and gain insight into the impact of metallicity on massive stellar winds. Combining high signal to noise (S/N) ratio spectroscopy in the UV and optical gives us access to diagnostics of multiple different physical processes in the stellar wind. We produce synthetic spectra using the stellar atmosphere modelling code FASTWIND, and reproduce the observed spectra using a genetic algorithm based fitting technique. We empirically constrain 15 physical parameters associated with the stellar and wind properties, including temperature, surface gravity, surface abundances, rotation, macroturbulence and wind parameters. We find, on average, mass-loss rates a factor of 4-5 lower than those predicted by Vink et al. 2001, in good agreement with predictions from Bjorklund et al. 2021, and the best agreement with those from Krticka et al. 2018. In the 'weak-wind' regime we find mass-loss rates orders of magnitude below any theoretical predictions. We find a positive correlation of clumping factors (fcl) with effective temperature with an average fcl = 14 +- 8 for the full sample. Above 38 kK an average 46 +- 24% of the wind velocity span is covered by clumps and the interclump density is 10-30% of the mean wind. Below an effective temperature of roughly 38 kK there must be additional light leakage for supergiants. For dwarf stars at low temperatures there is a statistical preference for very low clump velocity spans, however it is unclear if this can be physically motivated as there are no clearly observable wind signatures in UV diagnostics.

We report Bayesian inference of the mass, radius and hot X-ray emitting region properties - using data from the Neutron Star Interior Composition ExploreR (NICER) - for the brightest rotation-powered millisecond X-ray pulsar PSR J0437$\unicode{x2013}$4715. Our modeling is conditional on informative tight priors on mass, distance and binary inclination obtained from radio pulsar timing using the Parkes Pulsar Timing Array (PPTA) (Reardon et al. 2024), and we use NICER background models to constrain the non-source background, cross-checking with data from XMM-Newton. We assume two distinct hot emitting regions, and various parameterized hot region geometries that are defined in terms of overlapping circles; while simplified, these capture many of the possibilities suggested by detailed modeling of return current heating. For the preferred model identified by our analysis we infer a mass of $M = 1.418 \pm 0.037$ M$_\odot$ (largely informed by the PPTA mass prior) and an equatorial radius of $R = 11.36^{+0.95}_{-0.63}$ km, each reported as the posterior credible interval bounded by the 16% and 84% quantiles. This radius favors softer dense matter equations of state and is highly consistent with constraints derived from gravitational wave measurements of neutron star binary mergers. The hot regions are inferred to be non-antipodal, and hence inconsistent with a pure centered dipole magnetic field.

Pulse profile modeling of X-ray data from NICER is now enabling precision inference of neutron star mass and radius. Combined with nuclear physics constraints from chiral effective field theory ($\chi$EFT), and masses and tidal deformabilities inferred from gravitational wave detections of binary neutron star mergers, this has lead to a steady improvement in our understanding of the dense matter equation of state (EOS). Here we consider the impact of several new results: the radius measurement for the 1.42$\,M_\odot$ pulsar PSR J0437$-$4715 presented by Choudhury et al. (2024), updates to the masses and radii of PSR J0740$+$6620 and PSR J0030$+$0451, and new $\chi$EFT results for neutron star matter up to 1.5 times nuclear saturation density. Using two different high-density EOS extensions -- a piecewise-polytropic (PP) model and a model based on the speed of sound in a neutron star (CS) -- we find the radius of a 1.4$\,M_\odot$ (2.0$\,M_\odot$) neutron star to be constrained to the 95\% credible ranges $12.28^{+0.50}_{-0.76}\,$km ($12.33^{+0.70}_{-1.34}\,$km) for the PP model and $12.01^{+0.56}_{-0.75}\,$km ($11.55^{+0.94}_{-1.09}\,$km) for the CS model. The maximum neutron star mass is predicted to be $2.15^{+0.14}_{-0.16}\,$$M_\odot$ and $2.08^{+0.28}_{-0.16}\,$$M_\odot$ for the PP and CS model, respectively. We explore the sensitivity of our results to different orders and different densities up to which $\chi$EFT is used, and show how the astrophysical observations provide constraints for the pressure at intermediate densities. Moreover, we investigate the difference $R_{2.0} - R_{1.4}$ of the radius of 2$\,M_\odot$ and 1.4$\,M_\odot$ neutron stars within our EOS inference.

The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST gas phase chemical model. CRIR had the strongest effect on molecular abundance. The resultant molecular abundances were divided into three categories with different trends in time evolution. We compared our results with the observations of hot cores in the Large Magellanic Cloud (LMC). Our model fits best with the observations at a time of around $10^5$ years after the evaporation of ice and at the CRIR of $1.36 \times 10^{-16}$ s$^{-1}$. The resultant abundances of the oxygen-bearing complex organic molecules (COMs), such as CH$_3$OH, HCOOCH$_3$ and CH$_3$OCH$_3$, do not fit with observations in the same physical condition and may be located in a different physical environment. Our results suggest that investigating the CRIR value is crucial to predict the molecular evolution in LMC hot cores.

More than 3000 spectroscopically confirmed Type Ia supernovae (SNe Ia) are presented in the Zwicky Transient Facility SN Ia Data Release 2 (ZTF DR2). In this paper, we detail the spectral properties of 482 SNe Ia near maximum light, up to a redshift limit of $z$ $\leq$ 0.06. We measure the velocities and pseudo-equivalent widths (pEW) of key spectral features (Si II $\lambda$5972 and Si II $\lambda$6355) and investigate the relation between the properties of the spectral features and the photometric properties from the SALT2 light-curve parameters as a function of spectroscopic sub-class. We discuss the non-negligible impact of host galaxy contamination on SN Ia spectral classifications, as well as investigate the accuracy of spectral template matching of the ZTF DR2 sample. We define a new subclass of underluminous SNe Ia (`04gs-like') that lie spectroscopically between normal SNe Ia and transitional 86G-like SNe Ia (stronger Si II $\lambda$5972 than normal SNe Ia but significantly weaker Ti II features than `86G-like' SNe). We model these `04gs-like' SN Ia spectra using the radiative-transfer spectral synthesis code tardis and show that cooler temperatures alone are unable to explain their spectra; some changes in elemental abundances are also required. However, the broad continuity in spectral properties seen from bright (`91T-like') to faint normal SN Ia, including the transitional and 91bg-like SNe Ia, suggests that variations within a single explosion model may be able to explain their behaviour.

We use data from the MeerTime project on the MeerKAT telescope to ask whether the radio emission properties of millisecond pulsars (MSPs) and slowly rotating, younger pulsars (SPs) are similar or different. We show that the flux density spectra of both populations are similarly steep, and the widths of MSP pulsar profiles obey the same dependence on the rotational period as slow pulsars. We also show that the polarization of MSPs has similar properties to slow pulsars. The commonly used pseudo-luminosity of pulsars, defined as the product of the flux density and the distance squared, is not appropriate for drawing conclusions about the relative intrinsic radio luminosity of SPs and MSPs. We show that it is possible to scale the pseudo-luminosity to account for the pulse duty cycle and the solid angle of the radio beam, in such a way that MSPs and SPs do not show clear differences in intrinsic luminosity. The data, therefore, support common emission physics between the two populations in spite of orders of magnitude difference in their period derivatives and inferred, surface, dipole magnetic field strengths.

Fragmentation contributes to the formation and evolution of stars. Observationally, high-mass stars are known to form multiple-star systems, preferentially in cluster environments. Theoretically, Jeans instability has been suggested to determine characteristic fragmentation scales, and thermal or turbulent motion in the parental gas clump mainly contributes to the instability. To search for such a characteristic fragmentation scale, we have analyzed ALMA 1.33 mm continuum observations toward 30 high-mass star-forming clumps taken by the Digging into the Interior of Hot Cores with ALMA (DIHCA) survey. We have identified 573 cores using the dendrogram algorithm and measured the separation of cores by using the Minimum Spanning Tree (MST) technique. The core separation corrected by projection effects has a distribution peaked around 5800 au. In order to remove biases produced by different distances and sensitivities, we further smooth the images to a common physical scale and perform completeness tests. Our careful analysis finds a characteristic fragmentation scale of $\sim$7000 au, comparable to the thermal Jeans length of the clumps. We conclude that thermal Jeans fragmentation plays a dominant role in determining the clump fragmentation in high-mass star-forming regions, without the need of invoking turbulent Jeans fragmentation.

We propose a new framework to predict stellar properties from light curves. We analyze the light-curve data from the Kepler space mission and develop a novel tool for deriving the stellar rotation periods for main-sequence stars. Using this tool, we provide the largest (108785 stars) and most accurate (an average error of $1.6$ Days) sample of stellar rotations to date. Our model, LightPred, is a novel deep-learning model designed to extract stellar rotation periods from light curves. The model utilizes a dual-branch architecture combining Long Short-Term Memory (LSTM) and Transformer components to capture both temporal and global features within the data. We train LightPred on a dataset of simulated light curves generated using a realistic spot model and enhance its performance through self-supervised contrastive pre-training on Kepler light curves. Our evaluation demonstrates that LightPred outperforms classical methods like the Autocorrelation Function (ACF) in terms of accuracy and robustness. We apply LightPred to the Kepler dataset, generating the largest catalog to date of stellar rotation periods for main-sequence stars. Our analysis reveals a systematic shift towards shorter periods compared to previous studies, suggesting a potential revision of stellar age estimates. We also investigate the impact of stellar activity on period determination and find evidence for a distinct period-activity relation. Additionally, we confirm tidal synchronization in eclipsing binaries with orbital periods shorter than 10 days. Our findings highlight the potential of deep learning in extracting fundamental stellar properties from light curves, opening new avenues for understanding stellar evolution and population demographics.

Type Ia supernovae (SNe Ia) are widely believed to arise from thermonuclear explosions of white dwarfs (WDs). However, ongoing debate surrounds their progenitor systems and the mechanisms triggering these explosions. Recently, Sharon \& Kushnir showed that existing models do not reproduce the observed positive correlation between the $\gamma$-ray escape time, $t_0$, and the synthesized $^{56}$Ni mass, $M_\mathrm{Ni56}$. Their analysis, while avoiding complex radiation transfer (RT) calculations, did not account for the viewing-angle dependence of the derived $t_0$ and $M_\mathrm{Ni56}$ in multi-dimensional (multi-D) models during pre-nebular phases, where most observations performed. Here, we aim to identify an observational width-luminosity relation, similar to the $t_0$-$M_\mathrm{Ni56}$ relation to constrain multi-D models during pre-nebular phases while minimizing RT calculation uncertainties. We show that the bolometric luminosity at $t\le30$ days since explosion can be accurately computed without non-thermal ionization considerations, which are computationally expensive and uncertain. We find that the ratio of the bolometric luminosity at 30 days since explosion to the peak luminosity, $L_{30}/Lp$, correlates strongly with $t_0$. Using a sample of well-observed SNe Ia, we show that this parameter tightly correlates with the peak luminosity, $L_p$. We compare the observed $L_{30}/Lp$-$L_p$ distribution with models from the literature, including non-spherical models consisting of head-on WD collisions and off-centered ignitions of sub-Chandrasekhar mass WDs. We find that all known SNe Ia models fail to reproduce the observed bolometric luminosity-width correlation.

Ultra-high-energy cosmic rays are known to be mainly of extragalactic origin, and their propagation is limited by energy losses, so their arrival directions are expected to correlate with the large-scale structure of the local Universe. In this work, we investigate the possible presence of intermediate-scale excesses in the flux of the most energetic cosmic rays from the direction of the supergalactic plane region using events with energies above 20 EeV recorded with the surface detector array of the Pierre Auger Observatory up to 31 December 2022, with a total exposure of 135,000 km^2 sr yr. The strongest indication for an excess that we find, with a post-trial significance of 3.1{\sigma}, is in the Centaurus region, as in our previous reports, and it extends down to lower energies than previously studied. We do not find any strong hints of excesses from any other region of the supergalactic plane at the same angular scale. In particular, our results do not confirm the reports by the Telescope Array collaboration of excesses from two regions in the Northern Hemisphere at the edge of the field of view of the Pierre Auger Observatory. With a comparable exposure, our results in those regions are in good agreement with the expectations from an isotropic distribution.

The upcoming Simons Observatory (SO) Small Aperture Telescopes aim at observing the degree-scale anisotropies of the polarized CMB to constrain the primordial tensor-to-scalar ratio $r$ at the level of $\sigma(r=0)\lesssim0.003$ to probe models of the very early Universe. We present three complementary $r$ inference pipelines and compare their results on a set of sky simulations that allow us to explore a number of Galactic foreground and instrumental noise models, relevant for SO. In most scenarios, the pipelines retrieve consistent and unbiased results. However, several complex foreground scenarios lead to a $>2\sigma$ bias on $r$ if analyzed with the default versions of these pipelines, highlighting the need for more sophisticated pipeline components that marginalize over foreground residuals. We present two such extensions, using power-spectrum-based and map-based methods, and show that they fully reduce the bias on $r$ to sub-sigma level in all scenarios, and at a moderate cost in terms of $\sigma(r)$.

We report the discovery of a barium blue straggler star (BSS) in M67, exhibiting enhancements in slow neutron-capture ($s$-) process elements. Spectroscopic analysis of two BSSs (WOCS\,9005 \& WOCS\,1020) and 4 stars located near the main-sequence turn-off using GALAH spectra, showed that WOCS\,9005 has a significantly high abundance of the s-process elements ([Ba/Fe] = 0.75$\pm$0.08, [Y/Fe] = 1.09$\pm$0.07, [La/Fe] = 0.65$\pm$0.06). The BSS (WOCS\,9005) is a spectroscopic binary with a known period, eccentricity and a suspected white dwarf (WD) companion with a kinematic mass of 0.5 M$_\odot$. The first `sighting' of the WD in this barium BSS is achieved through multi-wavelength spectral energy distribution (SED) with the crucial far-UV data from the UVIT/\textit{AstroSat}. The parameters of the hot and cool companions are derived using binary fits of the SED using two combinations of models, yielding a WD with T$_{eff}$ in the range 9750--15250 K. Considering the kinematic mass limit, the cooling age of the WD is estimated as $\sim$ 60 Myr. The observed enhancements are attributed to a mass transfer (MT) from a companion asymptotic giant branch star, now a WD. We estimate the accreted mass to be 0.15 M$_{\odot}$, through wind accretion, which increased the envelope mass from 0.45 M$_{\odot}$. The detection of chemical enhancement, as well as the sighting of WD in this system have been possible due to the recent MT in this binary, as suggested by the young WD.

NEMESISPY is a Python package developed to perform parametric atmospheric modelling and radiative transfer calculation for the retrievals of exoplanetary spectra. It is a recent development of the well-established Fortran NEMESIS library (P. G. J. Irwin et al., 2008), which has been applied to the atmospheric retrievals of both solar system planets and exoplanets employing numerous different observing geometries. NEMESISPY can be easily interfaced with Bayesian inference algorithms to retrieve atmospheric properties from spectroscopic observations. Recently, NEMESISPY has been applied to the retrievals of Hubble and Spitzer data of a hot Jupiter (Yang et al., 2023), as well as to JWST/Mid-Infrared Instrument (JWST/MIRI) data of a hot Jupiter (Yang et al., 2024).

This study comprehensively investigates the gamma-ray dim population of Fanaroff-Riley Type 0 (FR0) radio galaxies as potentially significant sources of ultra-high-energy cosmic rays (UHECRs, E $>$ 10$^{18}$ eV) detected on Earth. While individual FR0 luminosities are relatively low compared to the more powerful Fanaroff-Riley Type 1 and Type 2 galaxies, FR0s are substantially more prevalent in the local universe, outnumbering the more energetic galaxies by a factor of $\sim$5 within a redshift of z $\leq$ 0.05. Employing CRPropa3 simulations, we estimate the mass composition and energy spectra of UHECRs originating from FR0 galaxies for energies above 10$^{18.6}$ eV. This estimation fits data from the Pierre Auger Observatory (Auger) using three extensive air shower models; both constant and energy-dependent observed elemental fractions are considered. The simulation integrates an isotropic distribution of FR0 galaxies, extrapolated from observed characteristics, with UHECR propagation in the intergalactic medium, incorporating various plausible configurations of extragalactic magnetic fields, both random and structured. We then compare the resulting emission spectral indices, rigidity cutoffs, and elemental fractions with recent Auger results. In total, 25 combined energy spectrum and mass composition fits are considered. Beyond the cosmic ray fluxes emitted by FR0 galaxies, this study predicts the secondary photon and neutrino fluxes from UHECR interactions with intergalactic cosmic photon backgrounds. The multi-messenger approach, encompassing observational data and theoretical models, helps elucidate the contribution of low luminosity FR0 radio galaxies to the total cosmic ray energy density.

We explore the feasibility of using machine-learning regression as a method of extracting basic stellar parameters and line-of-sight extinctions, given spectro-photometric data. To this end, we build a stable gradient-boosted random-forest regressor (xgboost), trained on spectroscopic data, capable of producing output parameters with reliable uncertainties from Gaia DR3 data (most notably the low-resolution XP spectra) without ground-based spectroscopic observations. Using Shapley additive explanations, we are able to interpret how the predictions for each star are influenced by each data feature. For the training and testing of the network, we use high-quality parameters obtained from the StarHorse code for a sample of around eight million stars observed by major spectroscopic surveys (APOGEE, GALAH, LAMOST, RAVE, SEGUE, and GES), complemented by curated samples of hot stars, very metal-poor stars, white dwarfs, and hot sub-dwarfs. The training data cover the whole sky, all Galactic components, and almost the full magnitude range of the Gaia DR3 XP sample of more than 217 million objects that also have parallaxes. We achieve median uncertainties (at $G\approx16$) of 0.20 mag in V-band extinction, 0.01 dex in logarithmic effective temperature, 0.20 dex in surface gravity, 0.18 dex in metallicity, and $12\%$ in mass (over the full Gaia DR3 XP sample, with considerable variations in precision as a function of magnitude and stellar type). We succeed in predicting competitive results based on Gaia DR3 XP spectra compared to classical isochrone fitting methods we employed in earlier work, especially for the parameters $A_V$, $T_{\rm eff}$, and metallicity. Finally, we showcase some applications of this new catalogue (e.g. extinction maps, metallicity trends in the Milky Way, extended maps of young massive stars, metal-poor stars, and metal-rich stars). [abridged]

Stellar oscillations are key to unravelling stars' properties, such as their mass, radius and age. Amplitudes of acoustic modes in solar-like stars are intrinsically linked to their convective turbulent excitation source, which in turn is influenced by magnetism. In the observations of the Sun and stars, the amplitude of the modes is modulated following their magnetic activity cycles: the higher the magnetic field, the lower the modes' amplitudes. When the magnetic field is strong, it can even inhibit the acoustic modes, which are not detected in a majority of solar-like stars presenting a strong magnetic activity. Magnetic fields are known to freeze convection when stronger than a critical value: an "on-off" approach is used in the literature. In this work, we investigate the impact of magnetic fields on the stochastic excitation of acoustic modes. First, we generalise the forced wave equation formalism, including the effects of magnetic fields. Second, we assess how convection is affected by magnetic fields using results from Magnetic Mixing-Length Theory. We provide the source terms of stochastic excitation, including a new magnetic source term and the Reynolds stresses. We provide scaling laws for the amplitudes of the modes, taking into account both the driving and the damping. Those scalings are based on the inverse Alfvén dimensionless parameter: the damping increases with the magnetic field and reaches a saturation threshold when the magnetic field is strong. The driving of the modes diminishes when the magnetic field becomes stronger, the turbulent convection being weaker. As expected from the observations, we find that a higher magnetic field diminishes the resulting modes amplitudes. Evaluating the inverse Alfvén number in stellar models provides a means to estimate the expected amplitudes of acoustic modes in magnetic active solar-type stars.

The first stars formed over five orders of magnitude in mass by accretion in primordial dark matter halos. We study the evolution of massive, very massive and supermassive primordial (Pop III) stars over nine orders of magnitude in accretion rate. We use the stellar evolution code GENEC to evolve accreting Pop III stars from 10$^{-6}$ - 10$^3$ M$_\odot$/yr and study how these rates determine final masses. The stars are evolved until either the end of central Si burning or until they encounter the general relativistic instability (GRI). We also examine how metallicity affects the evolution of the stars. At rates below $2.5 x 10^{-5}$ M$_\odot$/yr the final mass of the star falls below that required for pair-instability supernovae. The minimum rate required to produce black holes with masses above 250 M$_\odot$ is $5 x 10^{-5}$ M$_\odot$/yr, well within the range of infall rates found in numerical simulations of halos that cool via H$_2$, $10^{-3}$ M$_\odot$/yr. At rates of $5 x 10^{-5}$ M$_\odot$/yr to $4 x 10^{-2}$ \Ms\ yr$^{-1}$, like those expected for halos cooling by both H$_2$ and Ly-alpha, the star collapses after Si burning. At higher accretion rates the GRI triggers the collapse of the star during central H burning. Stars that grow at above these rates are cool red hypergiants with effective temperatures $log(T_{\text{eff}}) = 3.8$ and luminosities that can reach 10$^{10.5}$ L$_\odot$. At accretion rates of 100 - 1000 M$_\odot$/yr the gas encounters the general relativistic instability prior to the onset of central hydrogen burning and collapses to a black hole with a mass of 10$^6$ M$_\odot$ without ever having become a star. We reveal for the first time the critical transition rate in accretion above which catastrophic baryon collapse, like that which can occur during galaxy collisions in the high-redshift Universe, produces supermassive black holes via dark collapse.

We present a model independent analysis of the Pantheon+ supernova sample and study the dependence of the recovered values of $H_0$, $q_0$ and $j_0$ on the redshift cut and on the modeling of peculiar velocities. In addition to the bulk velocity discussed previously, we also find a significant infall that we attribute to the presence of an overdensity out to a radius of $R\simeq 120h^{-1}$Mpc.

Scattering transforms are a new type of summary statistics recently developed for the study of highly non-Gaussian processes, which have been shown to be very promising for astrophysical studies. In particular, they allow one to build generative models of complex non-linear fields from a limited amount of data, and have also been used as the basis of new statistical component separation algorithms. In the context of upcoming cosmological surveys, such as LiteBIRD for the cosmic microwave background polarization or Rubin-LSST and Euclid for study of the large scale structures of the Universe, the extension of these tools to spherical data is necessary. We develop scattering transforms on the sphere and focus on the construction of maximum-entropy generative models of several astrophysical fields. We construct, from a single target field, generative models of homogeneous astrophysical and cosmological fields, whose samples are quantitatively compared to the target fields using common statistics (power spectrum, pixel probability density function and Minkowski functionals). Our sampled fields agree well with the target fields, both statistically and visually. These generative models therefore open up a wide range of new applications for future astrophysical and cosmological studies; particularly those for which very little simulated data is available. We make our code available to the community so that this work can be easily reproduced and developed further.

Three-dimensional (3D) bubble structure of the Sgr-B molecular-cloud complex is derived by a kinematical analysis of CO-line archival cube data of the Galactic Centre (GC) observed with the Nobeyama 45-m telescope. The line-of-sight depth is estimated by applying the face-on transformation method of radial velocity to the projected distance on the Galactic plane considering the Galactic rotation of the central molecular zone (CMZ). The 3D complex exhibits a conical-horn structure with the Sgr-B2 cloud located in the farthest end on the line of sight at radial velocity $v_{\rm lsr} \sim 70$ km s$^{-1}$, and the entire complex composes a lopsided bubble opening toward the Sun at $v_{\rm lsr}\sim 50$ to 30 km s$^{-1}$. The line-of-sight extent of the complex is $\sim 100$ pc according to the large velocity extent for several tens of km s$^{-1}$ from Sgr B2 to the outskirts. The entire complex exhibits a flattened conical bubble with full sizes $\sim 40 {\rm pc} \times 20 {\rm pc} \times 100 {\rm pc}$ in the $l$, $b$ and line-of-sight directions, respectively. Based on the 3D analysis, we propose a formation scenario of the giant molecular bubble structure due to a galactic bow shock, and suggest that the star formation in Sgr B2 was enhanced by dual-side compression of the B2 cloud by the Galactic shock wave from up-stream and expanding HII region from the down-stream side of the GC Arm I in Galactic rotation.

The BL Lacertae (BL Lac) object OJ 287 underwent an intense X-ray activity phase, exhibiting its brightest recorded X-ray flare in 2016-2017, characterized by much softer X-ray spectra and, concurrently, its first-ever recorded very-high-energy (VHE) emission (100--560 GeV), reported by the VERITAS observatory. Broadband spectral energy distribution reveals a new jet emission component similar to high-synchrotron-peaked BL Lac objects, thereby implying the soft X-ray spectrum for the synchrotron emission. Using the advantage of simultaneous X-ray and VHE spectral information, as well as the source being a low-synchrotron-peaked BL Lac object, we systematically explored the extragalactic background light (EBL) spectrum by demanding that the VHE spectrum cannot be harder than the X-ray spectrum. We used three different phenomenological forms of the EBL spectral shape (power-law, parabola, and polynomial) motivated by current constraints on the EBL with the Bayesian Monte Carlo approach to infer the credible EBL range. Our study favors an almost flat power-law spectral shape and is consistent with previous studies. The other spectral forms capable of capturing curvature though result in a better statistics value; the improvement is statistically insignificant given the additional parameters.

A large population of intermediate-separation binaries, consisting of a main-sequence (MS) star and a white dwarf (WD), has recently emerged from Gaia's third data release (DR3), posing challenges to current models of binary evolution. Here we examine the $s$-process element abundances in these systems using data from GALAH DR3. Following refined sample analysis with parameter estimates based on GALAH spectra, we find a distinct locus where enhanced $s$-process elements depend on both the WD mass and metallicity, consistent with loci identified in previous asymptotic giant branch (AGB) nucleosynthesis studies with higher $s$-process yields. Notably, these enhanced abundances show no correlation with the systems' orbital parameters, supporting a history of accretion in intermediate-separation MS+WD systems. Consequently, our results form a direct observational evidence of a connection between AGB masses and $s$-process yields. We conclude by showing that the GALAH DR3 survey includes numerous Ba dwarf stars, within and beyond the mass range covered in our current sample, which can further elucidate $s$-process element distributions in MS+WD binaries.

Explaining the formation pathways of amides on ice-grain mantels is crucial to understanding the prebiotic chemistry in an interstellar medium. In this computational study, we explore different radical-neutral formation pathways for some of the observed amides (formamide, acetamide, urea, and N-methylformamide) via intermediate carbamoyl (NH2CO) radical precursors and their isomers. We assess the relative energy of four NH2CO isomers in the gas phase and evaluate their binding energy on small water clusters to discern the affinity that the isomers present to an ice model. We consider three possible reaction pathways for the formation of the carbamoyl radicals, namely, the OH + HCN, CN + H2O, and NH2 + CO reaction channels. We computed the binding energy distribution for the HCN and CH3CN precursors on an ice model consisting of a set of clusters of 22 water molecules each to serve as a starting point for the reactivity study on the ice surface. The computations revealed that the lowest barrier to the formation of an NH2CO isomer corresponds to the NH2 + CO reaction (12.6 kJ/mol). The OH + HCN reaction pathway results in the exothermic formation of the N-radical form of carbamoyl HN(C=O)H with a reaction barrier of 26.7 kJ/mol. We found that the CN + H2O reaction displays a high energy barrier of 70.6 kJ/mol. Finally, we also probed the direct formation of the acetamide radical precursor via the OH + CH3CN reaction and found that the most probable outcome on interstellar ices is the H-abstraction reaction to yield CH2CN and H2O. Based on these results, we believe that including alternative reaction pathways, leading to the formation of amides via the N-radical form of carbamoyl, would provide an improvement in the prediction of the amide abundances in astrochemical models, especially regarding the chemistry of star-forming regions.

A systematic study, based on the third-moment structure function, of Sgr A*'s variability finds an exponential rise time $\tau_{1,\rm{obs}}=14.8^{+0.4}_{-1.5}~\mathrm{minutes}$ and decay time $\tau_{2,\rm{obs}}=13.1^{+1.3}_{-1.4}~\mathrm{minutes}$. This symmetry of the flux-density variability is consistent with earlier work, and we interpret it as caused by the dominance of Doppler boosting, as opposed to gravitational lensing, in Sgr~A*'s light curve. A relativistic, semi-physical model of Sgr~A* confirms an inclination angle $i<45$ degrees. The model also shows that the emission of the intrinsic radiative process can have some asymmetry even though the observed emission does not. The third-moment structure function, which is a measure of the skewness of the light-curve increments, may be a useful summary statistic in other contexts of astronomy because it senses only temporal asymmetry, i.e., it averages to zero for any temporally symmetric signal.