Papers for Thursday, Jan 20 2022

Using the data from Gaia (ESA) Data Release 2 we performed the orbital calculations of globular clusters (GCs) of the Milky Way. To explore possible close encounters (or collisions) between the GCs, using our own developed high-order phi-GRAPE code, we integrated (backward and forward) the orbits of 119 objects with reliable positions and proper motions. In calculations, we adopted a realistic axisymmetric Galactic potential (bulge + disk + halo). Using different impact conditions, we found four pairs of the six GCs that may have experienced an encounter within twice the sum of the half-mass radii (collisions) over the last 5Gyr: Terzan3 - NGC 6553, Terzan 3 - NGC 6218, Liller 1 - NGC 6522 and Djorg 2 - NGC 6553.

The detection of Intermediate-Mass Black Holes (IMBHs) in dwarf galaxies is crucial to closing the gap in the wide mass distribution of black holes ($\sim 3 \, \rm M_{\odot}$ to $\sim 5 \times 10^{10} \, \rm M_{\odot}$). IMBHs originally located at the center of dwarfs that later collide with the Milky Way (MW) could be wandering, undetected, in our Galaxy. We used TNG50, the highest-resolution run of the IllustrisTNG project, to study the kinematics and dynamics of star clusters, in the appropriate mass range, acting as IMBH proxies in a MW analog galaxy. We showed that $\sim 87\%$ of our studied IMBHs drift inward. The radial velocity of these sinking IMBHs has a median magnitude of $\sim 0.44 \, \rm ckpc \, h^{-1} \, Gyr^{-1}$ and no dependence on the black hole mass. The central $1 \, \rm ckpc \, h^{-1}$ has the highest number density of IMBHs in the galaxy. A physical toy model with linear drag forces was developed to explain the orbital circularization with time. These findings constrain the spatial distribution of IMBHs, suggesting that future searches should focus on the central regions of the Galaxy. Additionally, we found that the 3D velocity distribution of IMBHs with respect to the galactic center has a mean of $\sim 180 \, \rm km \, s^{-1}$ and larger variance with decreasing radius. Remarkably, the velocity distribution relative to the local gas shows significantly lower values, with a mean of $\sim 88 \, \rm km \, s^{-1}$. These results are instrumental for predicting the accretion and radiation properties of IMBHs, facilitating their detection with future surveys.

The detection of the accelerated expansion of the Universe has been one of the major breakthroughs in modern cosmology. Several cosmological probes (CMB, SNe Ia, BAO) have been studied in depth to better understand the nature of the mechanism driving this acceleration, and they are being currently pushed to their limits, obtaining remarkable constraints that allowed us to shape the standard cosmological model. In parallel to that, however, the percent precision achieved has recently revealed apparent tensions between measurements obtained from different methods. These are either indicating some unaccounted systematic effects, or are pointing toward new physics. Following the development of CMB, SNe, and BAO cosmology, it is critical to extend our selection of cosmological probes. Novel probes can be exploited to validate results, control or mitigate systematic effects, and, most importantly, to increase the accuracy and robustness of our results. This review is meant to provide a state-of-art benchmark of the latest advances in emerging beyond-standard cosmological probes. We present how several different methods can become a key resource for observational cosmology. In particular, we review cosmic chronometers, quasars, gamma-ray bursts, standard sirens, lensing time-delay with galaxies and clusters, cosmic voids, neutral hydrogen intensity mapping, surface brightness fluctuations, secular redshift drift, and clustering of standard candles. The review describes the method, systematics, and results of each probe in a homogeneous way, giving the reader a clear picture of the available innovative methods that have been introduced in recent years and how to apply them. The review also discusses the potential synergies and complementarities between the various probes, exploring how they will contribute to the future of modern cosmology.

We present an analysis of the ultraluminous X-ray source (ULX) population in 75 Virgo cluster late-type galaxies, including all those with a star formation rate >~ 1 M_{sun}/yr and a representative sample of the less star-forming ones. This study is based on 110 observations obtained over 20 years with the Chandra X-ray Observatory Advanced Camera for Imaging Spectroscopy. As part of a Large Chandra Program, new observations were obtained for 52 of these 75 galaxies. The data are complete to a sensitivity of about 10^{39} erg/s, with a typical detection limit of about 3 x 10^{38} erg/s for the majority of the sources. The catalogue contains about 80 ULXs (0.3-10 keV luminosity >10^{39} erg/s), and provides their location, observed flux, de-absorbed luminosity, and (for the 25 most luminous ones) simple X-ray spectral properties. We discuss the ULX luminosity function in relation to the mass and star formation rate of the sample galaxies. We show that recent models of low-mass plus high-mass X-ray binary populations (scaling with stellar mass and star formation rate, respectively) are mostly consistent with our observational results. We tentatively identify the most luminous X-ray source in the sample (a source in IC 3322A with L_{X} ~ 6 x 10^{40} erg/s) as a recent supernova or its young remnant. The properties of the sample galaxies (morphologies, stellar masses, star formation rates, total X-ray luminosities from their point-source population) are also summarised.

We compute different sets of stellar evolutionary tracks in order to quantify the energy, mass, and metals yielded by massive main-sequence and post-main-sequence winds. Our aim is to investigate the impact of binary systems and of a metallicity-dependent distribution of initial rotational velocities on the feedback by stellar winds. We find significant changes compared to the commonly used non-rotating, single-star scenario. The largest differences are noticeable at low metallicity, where the mechanical-energy budget is substantially increased. So as to establish the maximal (i.e. obtained by neglecting dissipation in the near circumstellar environment) influence of winds on the early stages of galaxy formation, we use our new feedback estimates to simulate the formation and evolution of a sub-$L_*$ galaxy at redshift 3 (hosted by a dark-matter halo with a mass of $1.8\times 10^{11}$ M$_\odot$) and compare the outcome with simulations in which only supernova feedback is considered. Accounting for the continuous energy injection by winds reduces the total stellar mass, the metal content, and the burstiness of the star-formation rate as well as of the outflowing gas mass. However, our numerical experiment suggests that the enhanced mechanical feedback from the winds of rotating and binary stars has a limited impact on the most relevant galactic properties compared to the non-rotating single-star scenario. Eventually, we look at the relative abundance between the metals entrained in winds and those ejected by supernovae and find that it stays nearly constant within the simulated galaxy and its surrounding halo.

Photometric pipelines struggle to estimate both the flux and flux uncertainty for stars in the presence of structured backgrounds such as filaments or clouds. However, it is exactly stars in these complex regions that are critical to understanding star formation and the structure of the interstellar medium. We develop a method, similar to Gaussian process regression, which we term local pixelwise infilling (LPI). Using a local covariance estimate, we predict the background behind each star and the uncertainty on that prediction in order to improve estimates of flux and flux uncertainty. We show the validity of our model on synthetic data and real dust fields. We further demonstrate that the method is stable even in the crowded field limit. While we focus on optical-IR photometry, this method is not restricted to those wavelengths. We apply this technique to the 34 billion detections in the second data release of the Dark Energy Camera Plane Survey (DECaPS2). In addition to removing many $>3\sigma$ outliers and improving uncertainty estimates by a factor of $\sim 2-3$ on nebulous fields, we also show that our method is well-behaved on uncrowded fields. The entirely post-processing nature of our implementation of LPI photometry allows it to easily improve the flux and flux uncertainty estimates of past as well as future surveys.

Upper limits from the current generation of interferometers targeting 21-cm emission from high redshifts have recently begun to rule out physically realistic, though still extreme, models of the Epoch of Reionization (EoR). While inferring the detailed properties of the first galaxies is one of the most important motivations for 21-cm measurements, they can also provide useful constraints on the properties of the intergalactic medium (IGM). Motivated by this, we build a simple, phenomenological model for 21-cm fluctuations that works directly in terms of IGM properties, which bypasses the computationally expensive 3-D semi-numerical modeling generally employed in inference pipelines and avoids explicit assumptions about galaxy properties. The key simplifying assumptions are that (i) the ionization field is binary, and composed of spherical bubbles with an abundance described well by a parametric bubble size distribution, and (ii) that the spin temperature of the "bulk" IGM outside bubbles is uniform. Despite the simplicity of the model, the mean ionized fraction and spin temperature of the IGM recovered from mock 21-cm power spectra generated with 21cmFAST are in qualitative agreement with the true input values. This suggests that it is possible to obtain comparable constraints on the IGM from 21-cm measurements using models with very different assumptions, parameters, and priors. Our approach will thus be complementary to semi-numerical models as upper limits continue to improve in the coming years.

We have studied the unusual time variability of an ultraluminous X-ray source in M 101, 4XMM J140314.2$+$541806 (henceforth, J1403), using Chandra and XMM-Newton data. Over the last two decades, J1403 has shown short-duration outbursts with an X-ray luminosity $\sim1-3 \times 10^{39}$ erg s$^{-1}$, and longer intervals at luminosities $\sim0.5-1 \times 10^{38}$ erg s$^{-1}$. The bimodal behaviour and fast outburst evolution (sometimes only a few days) are more consistent with an accretor/propeller scenario for a neutron star than with the canonical outburst cycles of stellar-mass black holes. If this scenario is correct, the luminosities in the accretor and propeller states suggest a fast spin ($P \approx$ 5 ms) and a low surface magnetic field ($B \sim 10^{10}$ G), despite our identification of J1403 as a high-mass X-ray binary. The most striking property of J1403 is the presence of strong $\sim$600-s quasi periodic oscillations (QPOs), mostly around frequencies of $\approx 1.3-1.8$ mHz, found at several epochs during the ultraluminous regime. We illustrate the properties of such QPOs, in particular their frequency and amplitude changes between and within observations, with a variety of techniques (Fast Fourier Transforms, Lomb-Scargle periodograms, weighted wavelet Z-transform analysis). The QPO frequency range $<$10 mHz is an almost unexplored regime in X-ray binaries and ultraluminous X-ray sources. We compare our findings with the (few) examples of very low frequency variability found in other accreting sources, and discuss possible explanations (Lense-Thirring precession of the inner flow or outflow; radiation pressure limit-cycle instability; marginally stable He burning on the neutron star surface).

Are the kG-strength magnetic fields observed in young stars a fossil field left over from their formation or are they generated by a dynamo? Our previous numerical study concluded that magnetic fields must originate by a dynamo process. Here, we continue that investigation by performing even higher numerical resolution calculations of the gravitational collapse of a 1~M$_\odot$ rotating, magnetised molecular cloud core through the first and second collapse phases until stellar densities are reached. Each model includes Ohmic resistivity, ambipolar diffusion, and the Hall effect. We test six numerical resolutions, using between $10^5$ and $3\times10^7$ particles to model the cloud. At all but the lowest resolutions, magnetic walls form in the outer parts of the first hydrostatic core, with the maximum magnetic field strength located within the wall rather than at the centre of the core. At high resolution, this magnetic wall is disrupted by the Hall effect, producing a magnetic field with a spiral-shaped distribution of intensity. As the second collapse occurs, this field is dragged inward and grows in strength, with the maximum field strength increasing with resolution. As the second core forms, the maximum field strength exceeds 1~kG in our highest resolution simulations, and the stellar core field strength exceeds this threshold at the highest resolution. Our resolution study suggests that kG-strength magnetic fields may be implanted in low-mass stars during their formation, and may persist over long timescales given that the diffusion timescale for the magnetic field exceeds the age of the Universe.

We introduce an empirical methodology to study how the spectral energy distribution (SED) and galaxy morphology constrain each other and implement this on 8000 galaxies from the HST CANDELS survey in the GOODS-South field. We show that the SED does constrain morphology and present a method that quantifies the strength of the link between these two quantities. Two galaxies with very similar SEDs are around three times more likely to also be morphologically similar, with SED constraining morphology most strongly for relatively massive red ellipticals. We apply our methodology to explore likely upper bounds on the efficacy of morphological selection using colour. We show that, under reasonable assumptions, colour selection is relatively ineffective at separating homogeneous morphologies. Even with the use of up to six colours for morphological selection, the average purity in the resultant morphological classes is only around 60 per cent. While the results can be improved by using the whole SED, the gains are not significant, with purity values remaining around 70 per cent or below.

Hydrogen Ly${\alpha}$ haloes (LAHs) are commonly used as a tracer of the circumgalactic medium (CGM) at high redshifts. In this work, we aim to explore the existence of Ly${\alpha}$ haloes around individual UV-selected galaxies, rather than around Ly${\alpha}$ emitters (LAEs), at high redshifts. Our sample was continuum-selected with F775W<=27.5, and spectroscopic redshifts were assigned or constrained for all the sources thanks to the deepest (100- to 140-hour) existing Very Large Telescope (VLT)/Multi-Unit Spectroscopic Explorer (MUSE) data with adaptive optics. The final sample includes 21 galaxies that are purely F775W-magnitude selected within the redshift range z=2.9-4.4 and within a UV magnitude range -20<=M1500<= -18, thus avoiding any bias toward LAEs. We tested whether galaxy's Ly${\alpha}$ emission is significantly more extended than the MUSE PSF-convolved continuum component. We find 17 LAHs and four non-LAHs. We report the first individual detections of extended Ly${\alpha}$ emission around non-LAEs. The Ly${\alpha}$ halo fraction is thus as high as $81.0^{+10.3}_{-11.2}$%, which is close to that for LAEs at z=3-6 in the literature. This implies that UV-selected galaxies generally have a large amount of hydrogen in their CGM. We derived the mean surface brightness (SB) profile for our LAHs with cosmic dimming corrections and find that Ly${\alpha}$ emission extends to 5.4 arcsec (~40 physical kpc at the midpoint redshift z=3.6) above the typical 1${\sigma}$ SB limit. The incidence rate of surrounding gas detected in Ly${\alpha}$ per one-dimensional line of sight per unit redshift, dn/dz, is estimated to be $0.76^{+0.09}_{-0.09}$ for galaxies with M1500<= -18 mag at z~3.7. Assuming that Ly${\alpha}$ emission and absorption arise in the same gas, this suggests, based on abundance matching, that LAHs trace the same gas as damped Ly${\alpha}$ systems (DLAs) and sub-DLAs.

We study a model of two-field ultra-slow-roll (USR) inflation bounded by a curve in the field space. Curvature perturbations and non-Gaussianities can be enhanced both during the USR phase and from the inhomogeneities at the boundary. We employ the full non-linear $\delta N$ formalism to calculate the probability distribution function (PDF) for curvature perturbation non-perturbatively and show that the non-linear effects can significantly enhance the abundance of the primordial black holes (PBHs). For large curvature perturbations, the PDF has a universal exponential tail, but for the intermediate values, the PDF -- and, therefore, the abundance of the PBHs -- depend sensitively on the geometry of the boundary.

The spatial inhomogeneity is one of the important features for understanding the reionization process; however, it has not yet been fully quantified. To map this inhomogeneous distribution, we simultaneously detect Ly$\alpha$ emitters (LAEs) and Lyman break galaxies (LBGs) at $z \sim 6.6$ from the Subaru/Hyper Suprime-Cam (HSC) large-area ($\sim1.5\,\mathrm{ deg}^2 = 34000\,\mathrm{cMpc}^2$) deep survey. We estimate the neutral fraction, $x_\mathrm{HI}$, from the observed number density ratio of LAEs to LBGs, $n(\mathrm{LAE})/n(\mathrm{LBG})$ based on numerical radiative transfer simulation, in which model galaxies are selected to satisfy the observed selection function. While the average $x_\mathrm{HI}$ within the field of view is found to be $x_\mathrm{HI} < 0.4$, which is consistent with previous studies, the variation of $n(\mathrm{LAE})/n(\mathrm{LBG})$ within the field of view for each $140\,\mathrm{pMpc}^2$ is found to be as large as a factor of three. This may suggest a spatially inhomogeneous topology of reionization, but it also leaves open the possibility that the variation is based on the inherent large-scale structure of the galaxy distribution. Based on the simulations, it may be difficult to distinguish between the two from the current survey. We also find that LAEs in the high LAE density region are more populate high $\mathrm{EW}_0$, supporting that the observed $n(\mathrm{LAE})/n(\mathrm{LBG})$ is more or less driven by the neutral fraction, though the statistical significance is not high.

These notes introduce and review some of the physical principles underlying the theory of astrophysical accretion, emphasizing the central roles of angular momentum transport, angular momentum loss, and radiative cooling in determining the structure and evolution of accretion flows. Additional topics covered include the effective viscous theory of thin disks, classical instabilities of disk structure, the evolution of warped or eccentric disks, and the basic properties of waves within disks.

Accurate quantification of the column density of di-deuterated methanol is a key missing puzzle piece in the otherwise thoroughly constrained family of D-bearing methanol in the deeply embedded low-mass protostellar system and astrochemical template source IRAS16293-2422. A spectroscopic dataset for astrophysical purposes is built for CHD$_{2}$OH and made publicly available to facilitate accurate characterization of this species in astrochemical surveys. The newly computed line list and partition function are used to search for CHD$_{2}$OH towards IRAS16293-2422 A and B in data from ALMA-PILS. Only non-blended, optically thin lines of CHD$_{2}$OH are used for the synthetic spectral fitting. The constructed spectroscopic database contains line frequencies and strengths for 7417 transitions in the 0 to 500 GHz frequency range. ALMA-PILS observations in the 329-363 GHz range are used to identify 105 unique, non-blended, optically thin line frequencies of CHD$_{2}$OH for synthetic spectral fitting. The derived excitation temperatures and column densities yield high D/H ratios of CHD$_{2}$OH in IRAS 16293-2422 A and B of 7.5$\pm$1.1% and 7.7$\pm$1.2%, respectively. Deuteration in IRAS 16293-2422 is not higher than in other low-mass star-forming regions. Di-deuterated molecules consistently have higher D/H ratios than their monodeuterated counterparts in all low-mass protostars, which may be a natural consequence of H-D substitution reactions as seen in laboratory experiments. The Solar System's natal cloud, as traced by comet 67P/Churyumov-Gerasimenko, may have had a lower initial abundance of D, been warmer than the cloud of IRAS16293-2422, or been partially reprocessed. In combination with accurate spectroscopy, a careful spectral analysis, and a consideration of the underlying assumptions, successive deuteration is a robust window on the physicochemical provenance of star-forming systems.

We report a Giant Metrewave Radio Telescope HI 21cm mapping study of the neutral atomic hydrogen (HI) in the host galaxy of the fast radio burst (FRB) FRB20180916B at $z \approx 0.03399$. We find that the FRB host has an HI mass of $\rm M_{HI} = (2.74 \pm 0.33) \times 10^9 \ M_\odot$ and a high HI-to-stellar mass ratio, $\approx 1.3$. The FRB host is thus a gas-rich but near-quiescent galaxy, that is likely to have acquired a significant mass of HI in the recent past. The HI distribution is disturbed, with extended HI 21cm emission detected in a north-eastern tail, a counter-tail towards the south, an HI hole between the galaxy centre and the FRB location, and a high HI column density measured close to the FRB position. The FRB host is part of a group with four companions detected in their HI 21cm emission, the nearest of which is only 22~kpc from the FRB location. The gas-richness and disturbed HI distribution indicate that the FRB host has recently undergone a minor merger, which increased its HI mass, disturbed the HI in the galaxy disk, and compressed the HI near the FRB location to increase its surface density. We propose that this merger caused the burst of star-formation in the outskirts of the galaxy that gave rise to the FRB progenitor. The evidence for a minor merger is consistent with scenarios in which the FRB progenitor is a massive star, formed due to the merger event.

We make rotation curve fits to test the superfluid dark matter model. Our aim is to investigate whether superfluid dark matter provides satisfactory fits to galactic rotation curves with reasonable stellar mass-to-light ratios. We fitted the superfluid dark matter model to the rotation curves of 169 galaxies in the SPARC sample. We found that the mass-to-light ratios obtained with superfluid dark matter are generally acceptable in terms of stellar populations. However, the best fit mass-to-light ratios have an unnatural dependence on the size of the galaxy in that giant galaxies have systematically lower mass-to-light ratios than dwarf galaxies. A second finding is that the superfluid often fits the rotation curves best when the superfluid's force does not closely resemble that of Modified Newtonian Dynamics (MOND). In that case, we can no longer expect superfluid dark matter to reproduce the phenomenologically observed scaling-relations that make MOND appealing. If, on the other hand, we consider only solutions whose force approximates MOND well, then the total mass of the superfluid is in tension with gravitational lensing data. We conclude that even the best fits with superfluid dark matter are still unsatisfactory.

We study the non-thermal velocities in the quiet-sun using various high spatial, temporal, and spectral resolution observations from the Interface Region Imaging Spectrograph (IRIS). We focus our analysis on the transition region using the optically thin line (Si IV 1393.7 \AA), and select line profiles that are nearly Gaussian. We find evidence of a centre-to-limb variation using different observations having different exposure times, ranging from 5-30 s. The distribution of non-thermal velocities close to the limb are observed to peak around 20 km s$^{-1}$ while the disc observations show a peak around 15 km s$^{-1}$. The distributions are also different. The overall variation in the non-thermal velocities are correlated with the intensity of the line, as found previously. The on-disc velocities are smaller than most previous observations. In general, we find that the non-thermal velocities are independent of the selected exposure times. The Si IV lines didn't seem to exhibit any significant opacity effects. We conclude that these Doppler motions are mostly transverse to the radial direction. The possibility of swaying/torsional motions leading to such variations are validated from these IRIS observations.

A variety of formation models for dwarf spheroidal (dSph) galaxies have been proposed in the literature, but these generally have not been quantitatively compared with observations. We make use of a new spectroscopic data-set for the Milky Way dSph Leo I, combining 288 stars observed with Magellan/IMACS and existing Keck/DEIMOS data to provide velocity and metallicity measurements for 953 Leo I member stars. We search for chemo-dynamical patterns in this data-set, mock galaxies consisting of pure random motions, and simulated dwarfs formed via the dissolving star cluster and tidal stirring models. In the Leo I data, we report the detection of 14 candidate streams of stars that may have originated in disrupted star clusters. The angular momentum vectors of these streams are randomly oriented, consistent with the lack of rotation in Leo I. These results are consistent with the predictions of the dissolving cluster model. In contrast, we find fewer candidate stream signals in mock data-sets that lack coherent motions ~99% of the time. The chemo-dynamical analysis of the tidal stirring simulation produces streams that share a common orientation, which is inconsistent with the Leo~I data.

For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data is provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above $\sim$50 EeV is provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrinos clustering in the vicinity of UHECR directions. The second analysis searches for an excess of UHECRs in the direction of the highest-energy neutrinos. The third analysis searches for an excess of pairs of UHECRs and highest-energy neutrinos on different angular scales. None of the analyses has found a significant excess, and previously reported over-fluctuations are reduced in significance. Based on these results, we further constrain the neutrino flux spatially correlated with UHECRs.

We have conducted the first extensive observational survey of several deuterated species in 16 Class 0/I proto-brown dwarfs (proto-BDs) and 4 Class Flat/Class II brown dwarfs. Observations were obtained with the IRAM 30m telescope in the DCO$^{+}$ (3-2), DCN (3-2), DNC (3-2), and N$_{2}$D$^{+}$ (3-2) lines. The DCO$^{+}$/H$^{13}$CO$^{+}$, DCN/H$^{13}$CN, and DNC/HN$^{13}$C ratios are comparatively higher and show a narrower range than the DCO$^{+}$/HCO$^{+}$, DCN/HCN, and DNC/HNC ratios, respectively. The mean D/H ratios for the proto-BDs derived from these molecules are in the range of $\sim$0.02-3. Both low-temperature gas-phase ion-molecule deuteron transfer and grain surface reactions are required to explain the enhanced deuterium fractionation. The very dense and cold ($n_{H_{2}}$ $\geq$10$^{6}$ cm$^{-3}$, T $\leq$10 K) interior of the proto-BDs provide the suitable conditions for efficient deuterium fractionation in these cores. There is no correlation between the D/H ratios and the CO depletion factor, with the exception of the DCN/HCN ratios that show a strong anti-correlation possibly due to the difference in the peak emitting regions of the DCN and HCN molecules. Over a wide range in the bolometric luminosities spanning $\sim$0.002--40 L$_{\odot}$, we find a trend of higher DCO$^{+}$/HCO$^{+}$ (r = -0.7) and DCN/HCN (r = -0.6) ratios, nearly constant DNC/HNC (r = -0.4) and DNC/HN$^{13}$C (r = -0.1) ratios, lower N$_{2}$D$^{+}$/N$_{2}$H$^{+}$ ratios (r = 0.6) in the proto-BDs compared to protostars. Only one Class II brown dwarf shows emission in the DCO$^{+}$ (3-2) line. No correlation is seen between the D/H ratios and the evolutionary stage.

We report a study of the low-mass Class-0 multiple system VLA 1623AB in the Ophiuchus star-forming region, using H$^{13}$CO$^+$ ($J=3-2$), CS ($J=5-4$), and CCH ($N=3-2$) lines as part of the ALMA Large Program FAUST. The analysis of the velocity fields revealed the rotation motion in the envelope and the velocity gradients in the outflows (about 2000 au down to 50 au). We further investigated the rotation of the circum-binary VLA 1623A disk as well as the VLA 1623B disk. We found that the minor axis of the circum-binary disk of VLA 1623A is misaligned by about 12 degrees with respect to the large-scale outflow and the rotation axis of the envelope. In contrast, the minor axis of the circum-binary disk is parallel to the large-scale magnetic field according to previous dust polarization observations, suggesting that the misalignment may be caused by the different directions of the envelope rotation and the magnetic field. If the velocity gradient of the outflow is caused by rotation, the outflow has a constant angular momentum and the launching radius is estimated to be $5-16$ au, although it cannot be ruled out that the velocity gradient is driven by entrainments of the two high-velocity outflows. Furthermore, we detected for the first time a velocity gradient associated with rotation toward the VLA 16293B disk. The velocity gradient is opposite to the one from the large-scale envelope, outflow, and circum-binary disk. The origin of its opposite gradient is also discussed.

The role of charge exchange in shaping exoplanet photoevaporation remains a topic of contention. Exchange of electrons between stellar wind protons from the exoplanet's host star and neutral hydrogen from the planet's wind has been proposed as a mechanism to create "energetic neutral atoms" (ENAs), which could explain the high absorption line velocities observed in systems where mass loss is occurring. In this paper we present results from 3D hydrodynamic simulations of the mass loss of a planet similar to HD 209458b. We self-consistently launch a planetary wind by calculating the ionization and heating resulting from incident high-energy radiation, inject a stellar wind into the simulation, and allow electron exchange between the stellar and planetary winds. We predict the potential production of ENAs by the wind-wind interaction analytically, then present the results of our simulations, which confirm the analytic limits. Within the limits of our hydrodynamic simulation, we find that charge exchange with the stellar wind properties examined here is unable to explain the absorption observed at high Doppler velocities.

Stellar feedback is fundamental to the modeling of galaxy evolution as it drives turbulence and outflows in galaxies. Understanding the timescales involved are critical for constraining the impact of stellar feedback on the interstellar medium (ISM). We analyzed the resolved star formation histories along with the spatial distribution and kinematics of the atomic and ionized gas of four nearby star-forming dwarf galaxies (NGC 4068, NGC 4163, NGC 6789, UGC 9128) to determine the timescales over which stellar feedback drives turbulence. The four galaxies are within 5 Mpc and have a range of properties including current star formation rates of 0.0005 to 0.01 M$_{\odot}$ yr$^{-1}$, log(M$_*$/M$_{\odot}$) between 7.2 and 8.2, and log(M$_{HI}$/M$_\odot$) between 7.2 and 8.3. Their Color-Magnitude Diagram (CMD) derived star formation histories over the past 500 Myrs were compared to their atomic and ionized gas velocity dispersion and HI energy surface densities as indicators of turbulence. The Spearman's rank correlation coefficient was used to identify any correlations between their current turbulence and their past star formation activity on local scales ($\sim$400 pc). The strongest correlation found was between the HI turbulence measures and the star formation rate 100-200 Myrs ago. This suggests a coupling between the star formation activity and atomic gas on this timescale. No strong correlation between the ionized gas velocity dispersion and the star formation activity between 5-500 Myrs ago was found. The sample and analysis are the foundation of a larger program aimed at understanding the timescales over which stellar feedback drives turbulence.

We present radio spectra spanning $0.1 - 10$ GHz for the sample of heavily obscured luminous quasars with extremely red mid-infrared-optical colors and compact radio emission. The spectra are constructed from targeted 10 GHz observations and archival radio survey data, which together yield $6-11$ flux density measurements for each object. Our suite of Python tools for modeling the radio spectra is publicly available on Github. Our primary result is that most (61%) of the sample have peaked or curved radio spectra and many (36%) could be classified as Gigahertz Peaked Spectrum (GPS) sources. This indicates compact emission regions likely arising from recently triggered radio jets. Assuming synchrotron self-absorption (SSA) generates the peaks, we infer compact source sizes ($3 - 100$ pc) with strong magnetic fields ($6 - 100$ mG) and young ages ($30 - 10^4$ years). Conversely, free-free absorption (FFA) could also create peaks due to the high column densities associated with the deeply embedded nature of the sample. However, we find no correlations between the existence or frequency of the peaks and any parameters of the MIR emission. The high-frequency spectral indices are steep ($\alpha \approx -1$) and correlate, weakly, with the ratio of MIR photon energy density to magnetic energy density, suggesting that the spectral steepening could arise from inverse Compton scattering off the intense MIR photon field. This study provides a foundation for combining multi-frequency and mixed-resolution radio survey data for understanding the impact of young radio jets on the ISM and star formation rates of their host galaxies.

Infrared space interferometers can surpass the spatial resolution limitations of single-dish space telescopes. However, stellar interferometers from space have not been realized because of technical difficulties. Two beams coming from individual satellites separated by more than a few tens of meters should precisely interfere such that the optical-path and angular differences between the two beams are reduced at the wavelength level. Herein, we propose a novel beam combiner for space interferometers that records the spectrally-resolved interferometric fringes using the densified pupil spectroscopic technique. As the detector plane is optically conjugated to a plane, on which the two beams interfere, we can directly measure the relative phase difference between the two beams. Additionally, when an object within the field of view is obtained with a modest signal-to-noise ratio, we can extract the true complex amplitude from a continuous broadband fringe (i.e., one exposure measurement), without scanning a delay line and chopping interferometry. We discovered that this spectral imaging method is validated for observing the solar system objects by simulating the reflected light from Europa with a small stellar interferometer. However, because the structure of the object spectrum may cause a systematic error in the measurement, this method may be limited in extracting the true complex amplitude for other astronomical objects. Applying this spectral imaging method to general astrophysics will facilitate further research. The beam combiner and spectral imaging method are applied to a formation-flying stellar interferometer with multiple small satellites in a Sun-synchronous orbit for observation of the solar system objects in visible and near-infrared. We present an overview of SEIRIOS and the optimized optical design for a limited-volume spacecraft.

We present a new analysis of NuSTAR and Suzaku observations of the black hole Cygnus X-1 in the intermediate state. The analysis makes use of kerrC, a new model for analyzing spectral and spectropolarimetric X-ray observations of black holes. kerrC builds on a large library of simulated black holes in X-ray binaries. The model accounts for the X-ray emission from a geometrically thin, optically thick accretion disk, the propagation of the X-rays through the curved black hole spacetime, the reflection off the accretion disk, and the Comptonization of photons in coronae of different 3-D shapes and physical properties before and after the reflection. We present the results from using kerrC for the analysis of archival NuSTAR and Suzaku observations taken on May 27-28, 2015. We find that kerrC can account for the overall shape of the energy spectrum, but not for the broad spectral 6-7 keV feature, thought to be relativistically broadened Fe k-alpha emission from the inner region of the accretion flow. A wedge-shaped corona fits the data slightly better than a cone-shaped corona. The analysis indicates a black hole spin parameter a between 0.861 and 0.921. The kerrC model provides new insights about the radial distribution of the energy flux of returning and coronal emission irradiating the accretion disk. We use kerrC to predict the polarization signatures that the recently launched Imaging X-ray Polarimetry Explorer will detect and find small, but measurable, polarization fractions on the order of 1%.

Boasting supreme magnetic strengths, magnetars are among the prime candidates to generate fast radio bursts. Several theories have been proposed for the formation mechanism of magnetars, but have not yet been fully tested. As different magnetar formation theories expect distinct magnetar space velocity distributions, high-precision astrometry of Galactic magnetars can serve as a probe for the formation theories. In addition, magnetar astrometry can refine the understanding of the distribution of Galactic magnetars. This distribution can be compared against fast radio bursts (FRBs) localized in spiral galaxies, in order to test the link between FRBs and magnetars. Swift J1818.0-1607 is the hitherto fastest-spinning magnetar and the fifth discovered radio magnetar. In an ongoing astrometric campaign, we have observed Swift J1818.0-1607 for one year using the Very Long Baseline Array, and have determined a precise proper motion as well as a tentative parallax for the magnetar.

We investigate the transverse coronal-loop oscillations induced by the eruption of a prominence-carrying flux rope on 7 December 2012. The flux rope originating from NOAA Active Region (AR) 11621 was observed in EUV wavelengths by the SDO/AIA and in H$\alpha$ line center by the ground-based telescope at the BBSO. The early evolution of the flux rope is divided into two steps: a slow rise phase at a speed of $\approx$230\,km\,s$^{-1}$ and a fast rise phase at a speed of $\approx$706\,km\,s$^{-1}$. The eruption generates a C5.8 flare and the onset of the fast rise is consistent with the HXR peak time of the flare. The embedded prominence has a lower speed of $\approx$452\,km\,s$^{-1}$. During the early eruption of the flux rope, the nearby coronal loops are disturbed and experience independent kink-mode oscillations in the horizontal and vertical directions. The oscillation in the horizontal direction has an initial amplitude of $\approx$3.1\,Mm, a period of $\approx$294\,seconds, and a damping time of $\approx$645\,seconds. It is most striking in 171\,{\AA} and lasts for three to four cycles. The oscillations in the vertical directions are observed mainly in 171, 193, and 211\,{\AA}. The initial amplitudes lie in the range of 3.4\,--\,5.2\,Mm, with an average value of 4.5\,Mm. The periods are between 407\,seconds and 441\,seconds, with an average value of 423\,seconds. The oscillations are damping and last for nearly four cycles. The damping times lie in the range of 570\,--\,1012\,seconds, with an average value of 741\,seconds. Assuming a semi-circular shape of the vertically oscillating loops, we calculate the loop lengths according to their heights. Using the observed periods, we carry out coronal seismology and estimate the internal Alfv\'{e}n speeds (988\,--\,1145\,km\,s$^{-1}$) and the magnetic-field strengths (12\,--\,43\,G) of the oscillating loops.

We present $\sim$0."3 (114 pc) resolution maps of [CI] $^{3}P_{1}$-$^{3}P_{0}$ (hereafter [CI] (1-0)) and $^{12}$CO (1-0) obtained toward Arp 220 with the Atacama Large Millimeter/submillimeter Array. The overall distribution of the [CI] (1-0) emission is consistent with the CO (1-0). While the [CI] (1-0) and CO (1-0) luminosities of the system follow the empirical linear relation for the unresolved ULIRG sample, we find a sublinear relation between [CI] (1-0) and CO (1-0) using the spatially-resolved data. We measure the [CI] (1-0)/CO (1-0) luminosity ratio per pixel in star-forming environments of Arp 220 and investigate its dependence on the CO (3-2)/CO (1-0) ratio ($R_{\rm CO}$). On average, the [CI] (1-0)/CO (1-0) luminosity ratio is almost constant up to $R_{\rm CO} \simeq 1$ and then increases with $R_{\rm CO}$. According to the radiative transfer analysis, a high CI/CO abundance ratio is required in regions with high [CI] (1-0)/CO (1-0) luminosity ratios and $R_{\rm CO} > 1$, suggesting that the CI/CO abundance ratio varies at $\sim$100 pc scale in Arp 220. The [CI] (1-0)/CO (1-0) luminosity ratio depends on multiple factors and may not be straightforward to interpret. We also find the high-velocity components traced by [CI] (1-0) in the western nucleus, likely associated with the molecular outflow. The [CI] (1-0)/CO (1-0) luminosity ratio in the putative outflow is 0.87 $\pm$ 0.28, which is four times higher than the average ratio of Arp 220. While there is a possibility that the [CI] (1-0) and CO (1-0) emission traces different components, we suggest that the high line ratios are likely because of elevated CI/CO abundance ratios based on our radiative transfer analysis. A CI-rich and CO-poor gas phase in outflows could be caused by the irradiation of the cosmic rays, the shock heating, and the intense radiation field.

Recent advances in miniaturization and commercial availability of critical satellite subsystems and detector technology have made small satellites (SmallSats, including CubeSats) an attractive, low-cost potential solution for space weather research and operational needs. Motivated by the 1st International Workshop on SmallSats for Space Weather Research and Forecasting, held in Washington, DC on 1-4 August 2017, we discuss the need for advanced space weather measurement capabilities, driven by analyses from the World Meteorological Organization (WMO), and how SmallSats can efficiently fill these measurement gaps. We present some current, recent missions and proposed/upcoming mission concepts using SmallSats that enhance space weather research and provide prototyping pathways for future operational applications; how they relate to the WMO requirements; and what challenges remain to be overcome to meet the WMO goals and operational needs in the future. With additional investment from cognizant funding agencies worldwide, SmallSats -- including standalone missions and constellations -- could significantly enhance space weather research and, eventually, operations, by reducing costs and enabling new measurements not feasible from traditional, large, monolithic missions.

The final stage of gas giant formation involves accreting gas from the parent protoplanetary disk. In general, the infalling gas likely approaches a free-fall velocity, creating an accretion shock, leading to strong shock heating and radiation. We investigate the kinematics and energetics of such accretion shocks using 1D radiation hydrodynamic simulations. Our simulations feature the first self-consistent treatment of hydrogen dissociation and ionization, radiation transport, and realistic grey opacity. By exploring a broad range of giant planet masses (0.1-3 M$_{J}$) and accretion rates ($10^{-3}$-$10^{-2}$M$_{\oplus}\cdot\rm{yr}^{-1}$), we focus on global shock efficiency and the final entropy of the accreted gas. We find that radiation from the accretion shock can fully disassociate the molecular hydrogen of the incoming gas when the shock luminosity is above a critical luminosity. Meanwhile, the post-shock entropy generally fall into ``cold" ($<12k_{\rm{B}}/m_{\rm H}$) and ``hot" ($>16k_{\rm{B}}/m_{\rm H}$) groups which depends on the extent of the endothermic process of $\rm{H}_2$ dissociation. While 2D or 3D simulations are needed for more realistic understandings of the accretion process, this distinction likely carries over and sheds light on the interpretation of young direct imaging planets.

We present a model-fit pipeline to determine the stellar parameters of M-type dwarfs, which is an improvement upon our previous work described in Hejazi et al. 2020. We apply this pipeline to analyze the low-resolution (R~2000) spectra of 3745 M dwarfs/subdwarfs, collected at the MDM Observatory, Lick Observatory, Kitt Peak National Observatory, and Cerro Tololo Interamerican Observatory. We examine the variation of the inferred parameter values in the HR diagram constructed from their Gaia Early Data Release 3 (EDR3) parallaxes and optical magnitudes. We also study the distribution of our stars in the abundance diagram of [alpha/Fe] versus [M/H] and inspect the variation of their metallicity class, effective temperature, and surface gravity as well as their Galactic velocity components U, V, and W in this diagram. In addition, the analyses of the stars' projected motions in the two-dimensional UV, VW, and UW planes and the variation of their chemical parameters in these planes, and also their distribution in the abundance-velocity diagrams are important parts of this study. The precision of our model-fit pipeline is confirmed by the clear stratification of effective temperature and chemical parameters in the HR diagram, the similarity of the stars' distribution in the [alpha/Fe] versus [M/H] diagram and in the metallicity-velocity planes with those from other studies, revealing substructure in the abundance-velocity diagrams, and chemical homogeneity between the components of a set of binary systems.

Despite advances in observational data, theoretical models, and computational techniques to simulate key physical processes in the formation and evolution of galaxies, the stellar mass assembly of galaxies still remains an unsolved problem today. Optical spectroscopic measurements appear to show that the gas-phase metallicities of local ultra-luminous infrared galaxies (ULIRGs) are significantly lower than those of normal star-forming galaxies. This difference has resulted in the claim that ULIRGs are fueled by metal-poor gas accretion from the outskirts\cite{Mannucci10}. Here we report on a new set of gas-phase metallicity measurements making use of the far-infrared spectral lines of [O{\sc iii}]52 $\mu$m, [O{\sc iii}]88 $\mu$m, and [N{\sc iii}]57 $\mu$m instead of the usual optical lines. Photoionization models have resulted in a metallicity diagnostic based on these three lines that break the electron density degeneracy and reduce the scatter of the correlation significantly. Using new data from SOFIA and archival data from Herschel Space Observatory, we find that local ULIRGs lie on the mass-metallicity relation of star-forming galaxies and have metallicities comparable to other galaxies with similar stellar masses and star formation rates. The lack of a departure suggests that ULIRGs follow the same mass assembly mechanism as luminous star-forming galaxies and $\sim 0.3$ dex under-abundance in metallicities derived from optical lines is a result of heavily obscured metal-rich gas which has a negligible effect when using the FIR line diagnostics.

The rotation period of some planet-hosting stars appears to be in close commensurability with the orbital period of their close-by planets. A model is proposed to interpret such a phenomenon based on the excitation of resonant oscillations in the interior magnetic field of the star by a component of the tidal potential with a very low frequency in the reference frame rotating with the star. A magnetic flux tube located in the overshoot layer of the star is assumed to study the excitation of the resonant oscillations in the magnetostrophic regime. The model considers a planet on a circular oblique orbit and the growth timescale of the oscillations is estimated. To keep the system in resonance with the exciting potential, in spite of the variations in the magnetic field or tidal frequency, a self-regulating mechanism is proposed. The model is applied to ten systems and proves capable of accounting for the observed close commensurability in eight of them by assuming a magnetic field between $10^{2}$ and $10^{4}$ G. Systems with low-mass distant planets, such as AU Mic and HAT-P-11, cannot be interpreted by the proposed model. Consequences for the spin-orbit evolution of the systems, including dynamical tides and gyrochronology of planet-hosting stars, are discussed together with the effects on the chromospheric features produced by star-planet magnetic interactions

The magneto-frictional method is used in solar physics to compute both static and quasi-static models of the Sun's coronal magnetic field. Here, we examine how accurately magneto-friction (without fluid pressure) is able to predict the relaxed state in a one-dimensional test case containing two magnetic null points. Firstly, we show that relaxation under the full ideal magnetohydrodynamic equations in the presence of nulls leads necessarily to a non-force-free state, which could not be reached exactly by magneto-friction. Secondly, the magneto-frictional solutions are shown to lead to breakdown of magnetic flux conservation, whether or not the friction coefficient is scaled with magnetic field strength. When this coefficient is constant, flux is initially conserved, but only until discontinuous current sheets form at the null points. In the ensuing weak solution, we show that magnetic flux is dissipated at these current sheets. The breakdown of flux conservation does not occur for an alternative viscous relaxation scheme.

We compute the production of cosmic rays in the dynamical superbubble produced by a cluster of massive stars. Stellar winds, supernova remnants and turbulence are found to accelerate particles so efficiently that the nonlinear feedback of the particles must be taken into account in order to ensure that the energy balance is not violated. High energy particles do not scatter efficiently on the turbulence and escape quickly after each supernova explosion, which makes both their intensity inside the bubble and injection in the interstellar medium intermittent. On the other hand, the stochastic acceleration of low energy particles hardens the spectra at GeV energies. Because cosmic rays damp the turbulence cascade, this hardening is less pronounced when nonlinearities are taken into account. Nevertheless, spectra with hard components extending up to 1 to 10 GeV and normalised to an energy density of 1 to 100 eV cm$^{-3}$ are found to be typical signatures of cosmic rays produced in superbubbles. Efficient shock reacceleration within compact clusters is further shown to produce hard, slightly concave spectra, while the presence of a magnetised shell is shown to enhance the confinement of cosmic rays in the bubble and therefore the collective plasma effects acting on them. We eventually estimate the overall contribution of superbubbles to the galactic cosmic ray content and show typical gamma-ray spectra expected from hadronic interactions in superbuble shells. In both cases, a qualitative agreement with observations is obtained.

Automatic scheduling techniques are becoming a crucial tool for the efficient planning of large astronomical surveys. A specific scheduling method is being designed and developed for the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (Ariel) mission planning based on a hybrid meta-heuristic algorithm with global optimization capability to ensure obtaining satisfying results fulfilling all mission constraints. We used this method to simulate the Ariel mission plan, to assess the feasibility of its scientific goals, and to study the outcome of different science scenarios. We conclude that Ariel will be able to fulfill the scientific objectives, i.e. characterizing ~1000 exoplanet atmospheres, with a total exposure time representing about 75-80% of the mission lifetime. We demonstrate that it is possible to include phase curve observations for a sample of targets or to increase the number of studied exoplanets within the mission lifetime. Finally, around 12-15% of the time can still be used for non-time constrained observations.

X-ray polarimetric missions planned for this decade will significantly enhance our knowledge of compact accreting sources. Observations of the X-ray polarization signal from active galactic nuclei (AGNs) or X-ray binary systems (XRBs) will bring new means to study inner accretion flow in these objects that, together with currently used spectroscopic and timing techniques, will help us to determine better their properties, such as their inclination, orientation, shape, and size of their corona as well as the black hole spin. In this work, we present a yet missing piece in the global polarization models of black hole accretion discs. We compute the reflected X-ray emission from the disc in a local co-moving frame using (1) the radiative transfer code TITAN to obtain the ionization structure of the disc and (2) the Monte Carlo code STOKES that incorporates the physics of absorption, re-emission, and Compton scattering to produce a complete spectropolarimetric output. We present the final Stokes parameters I, Q, and U for a set of photon-indices of the incident primary power-law radiation, the disc ionization parameters, incident and emission angles, for three independent polarization states of the incident coronal X-ray photons with a sufficient resolution in energy to allow for sharp discussion of spectral and polarization properties. We show that the spectral component matches well literature predictions. The polarization degree and angle are in agreement with analytical approximations previously appearing in reflection models and we demonstrate that the polarized reflected X-ray emission can be, locally, quite large in the 2-12 keV band.

Situation with highly magnetized neutron stars in binary systems is not yet certain. On the one hand, all best studied magnetars seem to be isolated objects. On the other, there are many claims based on model-dependent analysis of spin properties or/and luminosity of neutron stars in X-ray binaries in favour of large fields. In addition, there are a few results suggesting a magnetar-like activity of neutron stars in close binary systems. Most of theoretical considerations do not favour even existence, not speaking about active decay, of magnetar-scale fields in neutron stars older than $\sim10^6$~yrs. However, alternative scenarios of the field evolution exist. I provide a brief review of theoretical and observational results related to the presence of neutron stars with large magnetic field in binaries and discuss perspectives of future studies.

The evolution of star-forming regions and their thermal balance are strongly influenced by their chemical composition, that, in turn, is determined by the physico-chemical processes that govern the transition between the gas phase and the solid state, specifically icy dust grains (e.g., particles adsorption and desorption). Gas-grain and grain-gas transitions as well as formation and sublimation of interstellar ices are thus essential elements of understanding astrophysical observations of cold environments (e.g., pre-stellar cores) where unexpected amounts of a large variety of chemical species have been observed in the gas phase. Adsorbed atoms and molecules also undergo chemical reactions which are not efficient in the gas phase. Therefore, the parameterization of the physical properties of atoms and molecules interacting with dust grain particles is clearly a key aspect to interpret astronomical observations and to build realistic and predictive astrochemical models. In this consensus evaluation, we focus on parameters controlling the thermal desorption of ices and how these determine pathways towards molecular complexity and define the location of snowlines, which ultimately influence the planet formation process. We review different crucial aspects of desorption parameters both from a theoretical and experimental point of view. We critically assess the desorption parameters commonly used in the astrochemical community for astrophysical relevant species and provide tables with recommended values. In addition, we show that a non-trivial determination of the pre-exponential factor nu using the Transition State Theory can affect the binding energy value. Finally, we conclude this work by discussing the limitations of theoretical and experimental approaches currently used to determine the desorption properties with suggestions for future improvements.

Cool main-sequence stars, such as the Sun, have magnetic fields which are generated by an internal dynamo mechanism. In the Sun, the dynamo mechanism produces a balance between the amounts of magnetic flux generated and lost over the Sun's 11-year activity cycle and it is visible in the Sun's different atmospheric layers using multi-wavelength observations. We used the same observational diagnostics, spanning several decades, to probe the emergence of magnetic flux on the two close by, active- and low-mass K dwarfs: 61 Cygni A and Epsilon Eridani. Our results show that 61 Cygni A follows the Solar dynamo with a regular cycle at all wavelengths, while Epsilon Eridani represents a more extreme level of the Solar dynamo, while also showing strong Solar-like characteristics. For the first time we show magnetic butterfly diagrams for stars other than the Sun. For the two K stars and the Sun, the rate at which the toroidal field is generated from surface poloidal field is similar to the rate at which toroidal flux is lost through flux emergence. This suggests that the surface field plays a crucial role in the dynamos of all three stars. Finally, for Epsilon Eridani, we show that the two chromospheric cycle periods, of ~3 and ~13 years, correspond to two superimposed magnetic cycles.

Small-scale, cyclic, transverse motions of plasma threads are usually seen in solar prominences, which are often interpreted as magnetohydrodynamic (MHD) waves. Here, we observed small-scale decayless transverse oscillations in a quiescent prominence, and they appear to be omnipresent. The oscillatory periods of the emission intensity and a proxy for the line-of-sight Doppler shift are about half period of the displacement oscillations. This feature agrees well with the fast kink-mode waves in a flux tube. All the moving threads oscillate transversally spatially in phase and exhibit no significant damping throughout the visible segments, indicating that the fast kink MHD waves are persistently powered and ongoing dissipating energy is transferred to the ambient plasma in the quiet corona. However, our calculations suggest that the energy taken by the fast kink MHD waves alone can not support the coronal heating on the quiet Sun.

The lack of detected intermediate mass black holes poses a gap in our understanding of the growth and evolution of the most exotic of astrophysical objects. Here we investigate the possibility of low-luminosity relativistic jets launched by intermediate mass black holes in the centers of dwarf galaxies. We built population models that allow us to make predictions for their radio emission and quantify their detectability by current and future surveys. We find that the upcoming instruments in optical and radio like the SKA, ngVLA and the Vera C. Rubin Observatory will likely be able to detect a significant fraction ($>38\%$) of such sources population if they exist. In addition, our results suggest that it is not unlikely a small number of midiquasars possibly masquerading as low-luminosity active galactic nuclei may have already been detected by existing surveys.

The early and complete temporal characterization of optical, fast, transient sources requires continuous and multi-band observations over different timescales (hours to months). For timing astronomy, the use of several telescopes to analyze single objects is the usual method, allowing the acquisition of highly sampled light curves. Taking a series of images each night helps to construct an uninterrupted chain of observations with a high cadence and low duty cycle. Speed is paramount, especially at early times in order to capture early features in the light curve that help determine the nature of the observed transients and assess their astrophysical interest. However, the problem of rapidly extracting source properties (temporal and color evolution) with a heterogeneous dataset remains. To address this, we present Muphoten, a general and fast-computation photometric pipeline, suitable for the calibration of transient brightness over multi-telescope and multi-band networks, with the goal of a single photometric time-series. We show the performance of Muphoten with observations of the optical transient SN 2018cow (from 06.2018 to 07.2018), monitored by the GRANDMA network and with the publicly available data of the Liverpool Telescope.

21cm tomography opens a window to directly study astrophysics and fundamental physics of early epochs in our Universe's history, the Epoch of Reionisation (EoR) and Cosmic Dawn (CD). Summary statistics such as the power spectrum omit information encoded in this signal due to its highly non-Gaussian nature. Here we adopt a network-based approach for direct inference of CD and EoR astrophysics jointly with fundamental physics from 21cm tomography. We showcase a warm dark matter (WDM) universe, where dark matter density parameter $\Omega_\mathrm{m}$ and WDM mass $m_\mathrm{WDM}$ strongly influence both CD and EoR. Reflecting the three-dimensional nature of 21cm light-cones, we present a new, albeit simple, 3D convolutional neural network for efficient parameter recovery at moderate training cost. On simulations we observe high-fidelity parameter recovery for CD and EoR astrophysics ($R^2>0.78-0.99$), together with DM density $\Omega_\mathrm{m}$ ($R^2>0.97$) and WDM mass ($R^2>0.61$, significantly better for $m_\mathrm{WDM}<3-4\,$keV). For realistic mock observed light-cones that include noise and foreground levels expected for the Square Kilometre Array, we note that in an optimistic foreground scenario parameter recovery is unaffected, while for moderate, less optimistic foreground levels (occupying the so-called wedge) the recovery of the WDM mass deteriorates, while other parameters remain robust against increased foreground levels at $R^2>0.9$. We further test the robustness of our network-based inference against modelling uncertainties and systematics by transfer learning between bare simulations and mock observations; we find robust recovery of specific X-ray luminosity and ionising efficiency, while DM density and WDM mass come with increased bias and scatter.

In the present work we have analysed the effect of dark matter haloes on the orbital and escape dynamics of stars in barred galaxies. For that, a three-dimensional gravitational model composed by central bulge, bar, disc and dark matter halo have been studied from the viewpoint of escape in an open Hamiltonian system. In addition this model is investigated for the following dark matter halo profiles viz. oblate and NFW. In both cases, escape mechanism has been observed near the saddle points corresponding to the bar ends. We visualise the nature of stellar orbits in the plane of the bar. Further Poincar\'e surface section maps in several phase planes for different escape energy values have been plotted to visualise the chaotic and regular domains of motion. Finally the variation of chaos with the dark matter halo parameters viz. mass, size, circular velocity and nature has been investigated. Our result shows that the oblate haloes are preferred to justify the formation of full-fledged spiral arms and extended dark matter distributions in the giant spirals than the NFW haloes, only if they host central super massive black holes (SMBHs). Again, in the absence of SMBHs, the oblate haloes well justify the formation of less prominent or poor spiral arms and dark matter dominated cores in the dwarf and LSB galaxies. We also found that, for the NFW haloes, extreme central baryonic feedback is required to form spiral patterns and such haloes should preferred for the galaxies with extremely energetic centres.

A novel collisionless shock jump condition is suggested by modeling the entropy production at the shock transition region. We also calculate downstream developments of the atomic ionization balance and the ion temperature relaxation in supernova remnants (SNRs). The injection process and subsequent acceleration of cosmic-rays (CRs) in the SNR shocks are closely related to the formation process of the collisionless shocks. The formation of the shock is caused by wave-particle interactions. Since the wave-particle interactions result in energy exchanges between electromagnetic fields and charged particles, the randomization of particles associated with the shock transition may occur with the rate given by the scalar product of the electric field and current. We find that order-of-magnitude estimates of the randomization with reasonable strength of the electromagnetic fields in the SNR constrain the amount of the CR nuclei and ion temperatures. The constrained amount of the CR nuclei can be sufficient to explain the Galactic CRs. The ion temperature becomes significantly lower than the case of no CRs. To distinguish the case without CRs, we perform synthetic observations of atomic line emissions from the downstream region of the SNR RCW~86. Future observations by {\it XRISM} and {\it Athena} can distinguish whether the SNR shock accelerates the CRs or not from the ion temperatures.

Young self-luminous giant exoplanets are expected to be oblate in shape owing to the high rotational speeds observed for some objects. Similar to the case of brown dwarfs, the thermal emission from these planets should be polarized by scatterings of molecules and condensate cloud particles, and the rotation-induced asymmetry of the planet's disk would yield to net non-zero detectable polarization. Considering an anisotropic atmosphere, we present here a three-dimensional approach to estimate the disk-averaged polarization that arises due to the oblateness of the planets. We solve the multiple-scattering vector radiative transfer equations at each location on the planet's disk and calculate the local Stokes vectors and then calculate the disk-integrated flux and linear polarization. For a cloud-free atmosphere, the polarization signal is observable only in the visible wavelength region. However, the presence of clouds in the planetary atmospheres leads to a detectable amount of polarization in the infrared wavelength region where the planetary thermal emission peaks. Considering different broad-band filters of the SPHERE-IRDIS instrument of the Very Large Telescope, we present generic models for the polarization at different wavelength bands as a function of their rotation period. We also present polarization models for the Exoplanets $\beta$ Pic b and ROXs 42B b as two representative cases which can guide future observations. Our insights on the polarization of young giant planets presented here would be useful for the upcoming polarimetric observations of the directly imaged planets.

A four-year sky survey with the use of the eROSITA telescope on board the Spektr-RG observatory will provide the best coverage in the soft (0.5-2 keV) and standard (2-10 keV) X-ray ranges, both in terms of sensitivity and angular resolution. We have analysed the possibility of detecting various types of isolated neutron stars with eROSITA. Among already known objects, eROSITA will be able to detect more than 160 pulsars, 21 magnetars, 7 central compact objects, all seven sources of the Magnificent Seven, and two other X-ray isolated neutron stars during the four-year survey mission.

Future high-resolution imaging X-ray observatories may require detectors with both fine spatial resolution and high quantum efficiency at relatively high X-ray energies (>5keV). A silicon imaging detector meeting these requirements will have a ratio of detector thickness to pixel size of six or more, roughly twice that of legacy imaging sensors. This implies greater diffusion of X-ray charge packets. We investigate consequences for sensor performance, reporting charge diffusion measurements in a fully-depleted, 50um thick, back-illuminated CCD with 8um pixels. We are able to measure the size distributions of charge packets produced by 5.9 keV and 1.25 keV X-rays in this device. We find that individual charge packets exhibit a gaussian spatial distribution, and determine the frequency distribution of event widths for a range of internal electric field strength levels. We find a standard deviation for the largest charge packets, which occur near the entrance window, of 3.9um. We show that the shape of the event width distribution provides a clear indicator of full depletion and infer the relationship between event width and interaction depth. We compare measured width distributions to simulations. We compare traditional, 'sum-above-threshold' algorithms for event amplitude determination to 2D gaussian fitting of events and find better spectroscopic performance with the former for 5.9 keV events and comparable results at 1.25 keV. The reasons for this difference are discussed. We point out the importance of read noise driven detection thresholds in spectral resolution, and note that the derived read noise requirements for mission concepts such as AXIS and Lynx may be too lax to meet spectral resolution requirements. While we report measurements made with a CCD, we note that they have implications for the performance of high aspect-ratio silicon active pixel sensors as well.

We search for the signature of parity-violating physics in the cosmic microwave background, called cosmic birefringence, using the Planck data release 4. We initially find a birefringence angle of $\beta=0.30\pm0.11$ (68% C.L.) for nearly full-sky data. The values of $\beta$ decrease as we enlarge the Galactic mask, which can be interpreted as the effect of polarized foreground emission. Two independent ways to model this effect are used to mitigate the systematic impact on $\beta$ for different sky fractions. We choose not to assign cosmological significance to the measured value of $\beta$ until we improve our knowledge of the foreground polarization.

If dark energy is a form of quintessence driven by a scalar field $\phi$ evolving down a monotonically decreasing potential $V(\phi)$ that passes sufficiently below zero, the universe is destined to undergo a series of smooth transitions: the currently observed accelerated expansion will cease; soon thereafter, expansion will come to end altogether; and the universe will pass into a phase of slow contraction. In this paper, we consider how short the remaining period of expansion can be given current observational constraints on dark energy. We also discuss how this scenario fits naturally with cyclic cosmologies and recent conjectures about quantum gravity.

Observations have shown that the disk frequency and the fraction of accreting pre-main-sequence stars decrease with the age of the population and that some stars appear to have disks while their accretion has stopped. Still, it is unclear how disk-bearing stars stop their accretion. To provide insight into the last stages of accretion in low-mass young stars, we conducted a survey of disk-bearing stars that are thought to be non-accretors to identify stars still accreting at very low rates. Here we present the first catalog of the survey of 170 disk-bearing non-accreting stars in Chamaeleon I, Orion OB1, Upper Scorpius, $\gamma$ Velorum, and Upper Centaurus Lupus, using He I $\lambda$10830 as a sensitive probe of accretion. We classify the line profiles into six types and argue that those showing redshifted and/or blueshifted absorption are still accreting. Using these classifications, we found that, among disk-bearing stars previously classified as non-accretors, at least 20-30% are still accreting, with a larger fraction of those at younger population ages. While the difference between the outer disk signature and accretion status is unclear, we find a difference between the inner disk excess and accretion status. There is no preference in the mass of the newly identified accretors, suggesting that the processes inhibiting accretion do not directly depend on mass in the typical mass range of T Tauri stars. Lastly, we found that at a low accretion level, the H$\alpha$ width at the 10% height criteria mischaracterizes a larger fraction of accretors than the line's equivalent width.

We present a precise characterization of the TOI-561 planetary system obtained by combining previously published data with TESS and CHEOPS photometry, and a new set of $62$ HARPS-N radial velocities (RVs). Our joint analysis confirms the presence of four transiting planets, namely TOI-561 b ($P = 0.45$ d, $R = 1.42$ R$_\oplus$, $M = 2.0$ M$_\oplus$), c ($P = 10.78$ d, $R = 2.91$ R$_\oplus$, $M = 5.4$ M$_\oplus$), d ($P = 25.7$ d, $R = 2.82$ R$_\oplus$, $M = 13.2$ M$_\oplus$) and e ($P = 77$ d, $R = 2.55$ R$_\oplus$, $M = 12.6$ M$_\oplus$). Moreover, we identify an additional, long-period signal ($>450$ d) in the RVs, which could be due to either an external planetary companion or to stellar magnetic activity. The precise masses and radii obtained for the four planets allowed us to conduct interior structure and atmospheric escape modelling. TOI-561 b is confirmed to be the lowest density ($\rho_{\rm b} = 3.8 \pm 0.5$ g cm$^{-3}$) ultra-short period (USP) planet known to date, and the low metallicity of the host star makes it consistent with the general bulk density-stellar metallicity trend. According to our interior structure modelling, planet b has basically no gas envelope, and it could host a certain amount of water. In contrast, TOI-561 c, d, and e likely retained an H/He envelope, in addition to a possibly large water layer. The inferred planetary compositions suggest different atmospheric evolutionary paths, with planets b and c having experienced significant gas loss, and planets d and e showing an atmospheric content consistent with the original one. The uniqueness of the USP planet, the presence of the long-period planet TOI-561 e, and the complex architecture make this system an appealing target for follow-up studies.

I propose a new scenario, the polar common envelope jets supernova (CEJSN) impostor scenario, to account for AT2018cow-like fast blue optical transients (FBOTs). The polar CEJSN impostor scenario evolves through four main phases. (1) A red supergiant (RSG) star expands to tidally interact with a neutron star (NS) companion (or a black hole). The interaction increases the RSG mass loss rate to form a circumstellar matter (CSM) halo to r~0.1pc. (2) Shortly before the onset of a common envelope evolution (CEE) and about a year before explosion the NS accretes mass from the RSG envelope and launches jets that inflate two opposite lobes in the CSM within ~100AU. (3) The NS-RSG system enters a CEE phase during which the system ejects most of the envelope mass in a dense equatorial outflow. (4) At the termination of the CEE the leftover envelope forms a circumbinary disk around the NS-core system. The NS accretes mass from the circumbinary disk and launches energetic jets that when collide with the fronts of the CSM lobes power an FBOT event. The low mass of the jets-lobes interaction zones and their large distance, of about 100AU, from the center account for the fast transient. In the future the core collapses to form a second NS. In the far future the two NS might merge. I suggest that FBOTs and similar fast transients are CEJSN impostors which compose a large fraction of the progenitors of NS-NS merger binaries.

A compact bound group of four active M-type dwarfs containing V1311 Ori is identified in the Gaia catalog of nearby stars. Located at a distance of 39 pc, it is likely related to the beta Pictoris and 32 Ori moving groups by kinematics, isochronal age, and other indicators of youth (Halpha emission, presence of lithium, and fast rotation). The brightest star A is a known close binary, for which a preliminary 80-yr visual-spectroscopic orbit is determined. Star B is resolved here into a 0.08" pair, and the faintest stars C and D are probably single. Considering the non-hierarchical configuration with projected separations of ~10 kau, this could be either a young sextuple system or a bound but dynamically unstable mini-cluster (trapezium) that avoided disruption so far. This pre-main-sequence system bridges the gap between moving groups and wide hierarchies.

Based on the Gaia EDR3 astrometric parameters and our new systemic radial velocity of the high-mass X-ray binary 4U 2206+54/BD+53 2790, we studied the trace back motion of the system and propose that it originated in the subgroup of the Cepheus OB1 association (Age~4-10 Myr) with its brightest star BD+53 2820 (B0V; L~$10^{4.7}$L$_\odot$). The kinematic age of 4U 2206+54 is about 2.8$\pm$0.4 Myr, it is at a distance of 3.1-3.3 kpc and has a space velocity of 75-100 km/s with respect to this member star (BD+53 2820) of the Cep OB1 association. This runaway velocity indicates that the progenitor of the neutron star hosted by 4U 2206+54 lost about 4-9 $M_{\odot}$ during the supernova explosion and the latter one received a kick velocity of at least 200-350 km/s. Since the high-mass X-ray binary 4U 2206+54/BD+53 2790 was born as a member of a subgroup of Cep OB1, the initially most massive star in the system terminated its evolution within ~7-9 Myr, corresponding to an initial mass >= 32$M_{\odot}$.

We present a full forward-modeled $w$CDM analysis of the KiDS-1000 weak lensing maps using graph-convolutional neural networks (GCNN). Utilizing the $\texttt{CosmoGrid}$, a novel massive simulation suite spanning six different cosmological parameters, we generate almost one million tomographic mock surveys on the sphere. Due to the large data set size and survey area, we perform a spherical analysis while limiting our map resolution to $\texttt{HEALPix}$ $n_\mathrm{side}=512$. We marginalize over systematics such as photometric redshift errors, multiplicative calibration and additive shear bias. Furthermore, we use a map-level implementation of the non-linear intrinsic alignment model along with a novel treatment of baryonic feedback to incorporate additional astrophysical nuisance parameters. We also perform a spherical power spectrum analysis for comparison. The constraints of the cosmological parameters are generated using a likelihood free inference method called Gaussian Process Approximate Bayesian Computation (GPABC). Finally, we check that our pipeline is robust against choices of the simulation parameters. We find constraints on the degeneracy parameter of $S_8 \equiv \sigma_8\sqrt{\Omega_M/0.3} = 0.78^{+0.06}_{-0.06}$ for our power spectrum analysis and $S_8 = 0.79^{+0.05}_{-0.05}$ for our GCNN analysis, improving the former by 16%. This is consistent with earlier analyses of the 2-point function, albeit slightly higher. Baryonic corrections generally broaden the constraints on the degeneracy parameter by about 10%. These results offer great prospects for full machine learning based analyses of on-going and future weak lensing surveys.

Extragalactic Fast X-ray Transients (FXRTs) are short flashes of X-ray photons spanning a few seconds to hours, with an uncertain origin. Our ignorance about their physical mechanisms and progenitor systems is due in part to the lack of clear multi-wavelength counterparts in most cases because they only have been identified serendipitously. We develop a systematic search of FXRTs using a straightforward X-ray flare search algorithm, in the Chandra Source Catalog (Data Release 2.0; 169.6 Ms over 592.4 deg$^{2}$ using only observations with $|b|>10^{\circ}$ and before 2015), incorporating various multi-wavelength constraints to rule out Galactic contamination and characterize the candidates. We report the detection of 14 FXRT candidates from a parent sample of 214,701 sources. Candidates have peak 0.5-7 keV fluxes between 1$\times$10$^{-13}$ to 2$\times$10$^{-10}$ erg cm$^{-2}$ s$^{-1}$ and $T_{90}$ values from 4 to 48 ks. The sample can be subdivided into two groups: six "nearby" FXRTs that occurred within $d\lesssim$100 Mpc and eight "distant" FXRTs with likely redshifts $\gtrsim$0.1. Three distant FXRT candidates exhibit light curves with a plateau (${\approx}$1-3 ks duration) followed by a power-law decay and X-ray spectral softening, similar to what was observed for the previously reported FXRT CDF-S~XT2, a proposed magnetar-powered binary neutron star merger event. After applying completeness corrections, we calculate event rates for the nearby and distant samples of 53.7$_{-15.1}^{+22.6}$ and 28.2$_{-6.9}^{+9.8}$ deg$^{-2}$ yr$^{-1}$, respectively. This novel sample of Chandra-detected extragalactic FXRT candidates, although modest in size, breaks new ground in terms of characterizing the diverse properties, nature, and possible progenitors of these enigmatic events.

The potential field source surface (PFSS) equations are commonly used to model the coronal magnetic field of the Sun and other stars. As with any computational model, solving equations using a numerical scheme introduces errors due to discretisation. We present a set of tests for quantifying these errors by taking advantage of analytic solutions to the PFSS equations when the input field is proportional to a single spherical harmonic. From the spherical harmonic solutions we derive analytic equations for magnetic field lines traced through the three dimensional magnetic field solution. We propose these as a set of standard analytic solutions that all PFSS solvers should be tested against to quantify their inherent errors. We apply these tests to the pfsspy software package, showing that it reproduces spherical harmonic solutions well with a slight overestimation of the unsigned open magnetic flux. It is also successful at reproducing analytic field line equations, with errors in field line footpoints typically much less than one degree.

We summarize the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with ESA and national space and research funding agencies.

Recently, particle in cell (PIC) simulations have shown that relativistic turbulence in collisionless plasmas can result in an equilibrium particle distribution function where turbulent heating is balanced by radiative cooling of electrons. Strongly magnetized plasmas are characterized by higher energy peaks and broader particle distributions. In relativistically moving astrophysical jets, it is believed that the flow is launched Poynting flux dominated and that the resulting magnetic instabilities may create a turbulent environment inside the jet, i.e., the regime of relativistic turbulence. In this paper, we extend previous PIC simulation results to larger values of plasma magnetization by linearly extrapolating the diffusion and advection coefficients relevant for the turbulent plasmas under consideration. We use these results to build a single zone turbulent jet model that is based on the global parameters of blazar emission region, and consistently calculate the particle distribution and resulting synchrotron and inverse Compton emission spectra. We then test our model by comparing its predictions with the broad-band quiescent emission spectra of a dozen blazars. Our results show good agreement with observations of low-synchrotron peaked (LSP) sources and find that LSPs are moderately Poynting flux dominated with magnetization $1\lesssim \sigma \lesssim 5$, have bulk Lorentz factor $\Gamma\sim 10-30$, and that the turbulent region is located at the edge, or just beyond, the broad line region (BLR). The turbulence is found to be driven at an area comparable to the jet cross section.

We give a detailed treatment of electromagnetic signals generated by gravitational waves (GWs) in resonant cavity experiments. Our investigation corrects and builds upon previous studies by carefully accounting for the gauge dependence of relevant quantities. We work in a preferred frame for the laboratory, the proper detector frame, and show how to resum short-wavelength effects to provide analytic results that are exact for GWs of arbitrary wavelength. This formalism allows us to firmly establish that, contrary to previous claims, cavity experiments designed for the detection of axion dark matter only need to reanalyze existing data to search for high-frequency GWs with strains as small as $h\sim 10^{-22}-10^{-21}$. We also argue that directional detection is possible in principle using readout of multiple cavity modes. Further improvements in sensitivity are expected with cutting-edge advances in superconducting cavity technology.

There is growing interest in the detection and characterization of gravitational waves from postmerger oscillations of binary neutron stars. These signals contain information about the nature of the remnant and the high-density and out-of-equilibrium physics of the postmerger processes, which would complement any electromagnetic signal. However, the construction of binary neutron star postmerger waveforms is much more complicated than for binary black holes: (i) there are theoretical uncertainties in the neutron-star equation of state and other aspects of the high-density physics, (ii) numerical simulations are expensive and available ones only cover a small fraction of the parameter space with limited numerical accuracy, and (iii) it is unclear how to parametrize the theoretical uncertainties and interpolate across parameter space. In this work, we describe the use of a machine-learning method called a conditional variational autoencoder (CVAE) to construct postmerger models for hyper/massive neutron star remnant signals based on numerical-relativity simulations. The CVAE provides a probabilistic model, which encodes uncertainties in the training data within a set of latent parameters. We estimate that training such a model will ultimately require $\sim 10^4$ waveforms. However, using synthetic training waveforms as a proof-of-principle, we show that the CVAE can be used as an accurate generative model and that it encodes the equation of state in a useful latent representation.

We study the observation of stochastic gravitational-wave background (SGWB) made by pulsar-timing arrays in the spherical harmonic space. Instead of using the Shapiro time delay, we keep the Sachs-Wolfe line-of-sight integral for the timing residual of an observed pulsar. We derive the power spectrum of the timing residual, from which the overlap reduction functions and the bipolar spherical harmonics coefficients are constructed for the SGWB intensity and polarization anisotropies. We have reproduced the previous results, noting that we have developed a fast algorithm for computing accurate overlap reduction functions and the bipolar spherical harmonics coefficients for the linear-polarization anisotropy are worked out for the first time. Our harmonic-space method is useful for future pulsar-timing-array observation on a few thousand pulsars and provides optimal estimators for testing the statistical isotropy of the SGWB.

The authors investigate how teaching art and astronomy together has the potential to inspire new art forms, enhance scientific public outreach, and promote art and science education. The authors teach an astro-animation class at the Maryland Institute College of Art in partnership with NASA scientists. The animations explore science in creative ways. Astrophysicists, educators, students, and the general public were surveyed to evaluate the experiences, and benefits from this project. The responses were very positive - the program is an effective way to stimulate art students to learn science, share an artist's viewpoint beyond the classroom, and engage with the public.

We propose a mechanism that forms primordial black holes (PBHs) via a first-order electroweak phase transition (FOEWPT). The FOEWPT is realized by extending the Standard Model with a real singlet scalar, while the PBH formation is achieved by the collapse of non-topological solitons called Fermi-balls. Such solitons form via trapping fermions in the false vacuum during the FOEWPT, and they eventually collapse into PBHs due to the internal Yukawa attractive force. We demonstrate that a scenario with PBH dark matter candidate can exist, and the typical experimental signals include FOEWPT gravitational waves and the multi-lepton/jet or displaced vertex final states at the LHC.

We suggest a new explanation for the observed large scale flatness, homogeneity and isotropy of the universe. The basic ingredients are elementary and well-known, namely Einstein's theory of gravity and Hawking's method of computing gravitational entropy. The new twist is provided by the boundary conditions we recently proposed for "big bang" type singularities dominated by conformal matter, enforcing $CPT$ symmetry and analyticity. Here, we show that, besides allowing us to describe the big bang, these boundary conditions allow new gravitational instantons, enabling us to calculate the gravitational entropy of cosmologies which include radiation, dark energy and space curvature of either sign. We find the gravitational entropy of these universes, $S_g \sim S_\Lambda^{1/ 4} S_r$, where $S_\Lambda$ is the famous de Sitter entropy and $S_r$ is the total entropy in radiation. To the extent that $S_g$ exceeds $S_\Lambda$, the most probable universe is flat. By analysing the perturbations about our new instantons, we argue it is also homogeneous and isotropic on large scales.

So far, most of the developments in muography (or cosmic-ray muon radiography) have been based on either the scattering or the absorption of cosmic-ray muons produced by the nuclear interactions between primary cosmic-rays and the nuclei of the Earth's atmosphere. Applications of muography are increasing in various disciplines. A new use of this technique to measure a magnetic field has recently been proposed by our group. This new application takes advantage of the electric charge of cosmic-ray muons, which causes them to change their trajectory due to the Lorentz force generated by a magnetic field. In this study, we present a feasibility study of the proposed technique by simulating a simple dipole magnet using the three-dimensional finite element solution package AMaze, together with the PHITS Monte Carlo simulation tools. The distribution of magnetic field flux densities around the magnet was calculated in AMaze and entered into the PHITS code. Positive and negative cosmic-ray muons were generated based on the PHITS-based analytical radiation model (PARMA). A comparison of the count rate maps of the detected muons on two position-sensitive scintillator detectors for the magnetic field ON and OFF was studied using PHITS. The simulation results show the effect of the magnet on the count rate maps and are promising for the newly proposed application of cosmic-ray muons, the imaging of a magnetic field.

We investigate the effect of peculiar velocities of inhomogeneities and the spatial curvature of the universe on the shape of the gravitational potential. To this end, we consider scalar perturbations of the FLRW metric. The gravitational potential satisfies a Helmholtz-type equation which follows from the system of linearized Einstein equations. We obtain analytical solutions of this equation in the cases of open and closed universes, filled with cold dark matter in presence of the cosmological constant. We demonstrate that, first, peculiar velocities significantly affect the screening length of the gravitational interaction and, second, the form of the gravitational potential depends on the sign of the spatial curvature.