Papers for Thursday, Jul 07 2022

We present the structural parameters of $\sim910$ dwarf elliptical-like galaxies in the local universe ($z\lesssim0.01$) derived from the $r-$band images of the Sloan Digital Sky Survey (SDSS). We examine the dependence of structural parameters on the morphological types (dS0, dE,dE$_{bc}$, dSph, and dE$_{blue}$). There is a significant difference in the structural parameters among the five sub-types if we properly treat the light excess due to nucleation in dSph and dE galaxies. The mean surface brightness within the effective radius ($<\mu_{e}>$) of dSph galaxies is also clearly different from that of other sub-types. The frequency of disk features such as spiral arms depends on the morphology of dwarf galaxies. The most pronounced difference between dSph galaxies and other sub-types of early-type dwarf galaxies is the absence of disk feature which is thought to be closely related to their origin.

We employ several galaxy formation models, in particular, L-GALAXIES, IllustrisTNG, and EAGLE, as well as observational samples from SDSS and DESI, to investigate galactic conformity, the observed large-scale correlation between the star-formation properties of central (primary) galaxies and those of their neighbours. To analyse the models and observations uniformly, we introduce CENSAT, a new algorithm to define whether a galaxy is a central or a satellite system based on an isolation criterion. We find that the conformity signal is present, up to at least 5 Mpc from the centres of low- and intermediate-mass centrals in the latest version of L-GALAXIES (Ayromlou et al. 2021), IllustrisTNG, and EAGLE, as well as in SDSS and DESI observational samples. In comparison, the conformity signal is substantially weaker in an older version of L-GALAXIES (Henriques et al. 2020). One of the main differences between this older model and the other models is its neglect of ram-pressure stripping of the gas reservoirs of galaxies except within the boundaries of massive cluster haloes. Our observational comparisons demonstrate that this difference significantly affects the observed large-scale conformity signal. Furthermore, by examining the contribution of backsplash, fly-by, central, and satellite galaxies to the conformity signal, we show that much, but not all, of it arises from primary galaxies near massive systems. Remaining tensions between the models and observations may be solved by modifying the physical prescriptions for how feedback processes affect the distribution and kinematics of gas and the environment around galaxies out to scales of several Megaparsecs.

We analyze spectroscopic observations of five young massive clusters (YMCs) in the barred spiral galaxy NGC 1313 to obtain detailed abundances from their integrated light. Our sample of YMCs was observed with the X-Shooter spectrograph on the Very Large Telescope (VLT). We make use of theoretical isochrones to generate synthetic integrated-light spectra, iterating on the individual elemental abundances until converging on the best fit to the observations. We measure abundance ratios for [Ca/Fe], [Ti/Fe], [Mg/Fe], [Cr/Fe], and [Ni/Fe]. We estimate an Fe abundance gradient of $-$0.124 $\pm$ 0.034 dex kpc$^{-1}$, and a slightly shallower $\alpha$ gradient of $-$0.093 $\pm$ 0.009 dex kpc$^{-1}$. This is in contrast to previous metallicity studies that focused on the gas-phase abundances, which have found NGC 1313 to be the highest-mass barred galaxy known not to have a radial abundance gradient. We propose that the gradient discrepancy between the different studies originates from the metallicity calibrations used to study the gas-phase abundances. We also observe an age-metallicity trend which supports a scenario of constant star formation throughout the galaxy, with a possible burst in star formation in the south-west region where YMC NGC 1313-379 is located.

The "no-hair" theorem can, in principle, be tested at the center of the Milky Way by measuring the spin and the quadrupole moment of Sgr A$^*$ with the orbital precession of S-stars, measured over their full periods. Contrary to the original method, we show why it is possible to test the no-hair theorem using observations from only a single star, by measuring precession angles over a half-orbit. There are observational and theoretical reasons to expect S-stars to spin rapidly, and we have quantified the effect of stellar spin, via spin-curvature coupling (the leading-order manifestation of the Mathisson-Papapetrou-Dixon equations), on future quadrupole measurements. We find that they will typically suffer from errors of order a few percentage points, but for some orbital parameters, the error can be much higher. We re-examine the more general problem of astrophysical noise sources that may impede future quadrupole measurements, and find that a judicious choice of measurable precession angles can often eliminate individual noise sources. We have derived optimal combinations of observables to eliminate the large noise source of mass precession, the novel noise of spin-curvature coupling due to stellar spin, and the more complicated noise source arising from transient quadrupole moments in the stellar potential.

The Milky Way's center is the closest galaxy nucleus and the most extreme environment of the Galaxy. Although its volume is less than 1% of that of the Galactic disk, up to 10% of all new-born stars in the Galaxy in the past 100 Myr formed there. Therefore, it constitutes a perfect laboratory to understand star formation under extreme conditions, similar to those in starburst or high-redshift galaxies. However, the only two known Galactic center young clusters account for <10% of the expected young stellar mass. We analyze the star formation history of Sagittarius (Sgr) B1, a Galactic center region associated with strong HII emission, and find evidence for the presence of several $10^5$ solar masses of young stars, that formed $\sim$10 Myr ago. We also detect the presence of intermediate age stars (2-7 Gyr) in Sgr B1 that appear to be rare (or absent) in the inner regions of the nuclear stellar disk, and might indicate inside out formation. Our results constitute a large step toward a better understanding of star formation at the Galactic center, such as the fate of young clusters, and the possibly different initial mass function in this region.

We use the APOSTLE suite of Local Group (LG) cosmological hydrodynamical simulations to examine the properties of "backsplash" galaxies, i.e, dwarfs outside the virial radius, $r_{200}$, of the Milky Way (MW) or M31 which may have been within their virial boundaries in the past. More than half of all dwarfs at distances between one and two virial radii of each primary are backsplash galaxies. More distant backsplash systems, i.e., those that reach distances well beyond $2\, r_{200}$, are typically systems close to apocentre of nearly radial orbits, and, therefore, essentially at rest relative to their primary. We use this result to investigate which LG dwarfs beyond $\sim 500$ kpc of either primary could be a backsplash satellite of either MW or M31. The Tucana dwarf spheroidal (dSph), one of the few known quiescent LG field dwarfs, at $d_{\rm M31}\approx 1350$ kpc and $d_{\rm MW}\approx 880$ kpc, is a promising candidate. Tucana's radial velocity suggests it is at rest relative to M31. Further, Tucana is located close to the orbital plane of M33 around M31, and simple orbit integrations indicate that Tucana may have been ejected during an early pericentric passage of M33 about $\sim 11$ Gyr ago, a timing which approximately coincides with Tucana's last episode of star formation. We suggest that Tucana may have been a satellite of M31 or M33, providing a compelling explanation for its puzzling lack of gas and ongoing star formation despite its isolated nature.

We present the weak lensing mass distribution of a triple merging cluster candidate at $z_{\rm photo}\sim 0.36$ belonging to a supercluster recently discovered during the eROSITA Performance Verification phase. Our analysis solved a previous tension in the merger classification by confirming that the cluster pair eFEDS J093513.3+004746 and eFEDS J093510.7+004910 is undergoing a major merger with a mass ratio $1.7_{-0.7}^{+0.5}$. According to our two-body kinematic description, the encounter happened $0.58_{-0.20}^{+0.15}$ Gyr ago, in a scenario that supports the observed radio relic position at the cluster outskirts. However, the same analysis showed that the companion cluster, eFEDS J093501.1+005418, is not gravitationally bound to the interacting system and therefore it is not part of the supercluster. We also checked the impact of adopting a scaling relation to determine the halo concentration $c_{200}$. At the observed merger stage, where the clusters have travelled $\sim$55 per cent of the path to reach the apoapsis, the choice of the $c_{200}$ (whether from a scaling relation or a free parameter in the mass model) does not change significantly either the cluster masses or the kinematic description.

Studies of the high-redshift rest-frame ultraviolet (UV) luminosity functions (LFs) have typically treated the star-forming galaxy and active galactic nuclei (AGN) populations separately, as they have different survey depth and area requirements. However, the recent advent of wide-area deep ground-based imaging surveys now probe volumes large enough to discover AGNs, at depths sensitive enough for fainter star-forming galaxies, bridging these two populations. Using results from such surveys as observational constraints, we present a methodology to jointly empirically model the evolution of the rest-UV luminosity functions at z=3-9. We assume both populations have a LF well-described by a double power law modified to allow a flattening at the faint-end, and that all LF parameters evolve smoothly with redshift. This provides a good fit to the observations, and makes predictions to volume densities and redshifts not yet observed. We find that the volume density of bright (M_UV = -28) AGNs rises by five orders of magnitude from z=9 to z=3, while modestly bright (M_UV = -21) galaxies rise by only two orders of magnitude across the same epoch. The observed bright-end flattening of the z=9 LF is unlikely to be due to AGN, and rather is due to a shallowing of the bright-end slope, implying reduced feedback in bright galaxies at early times. Integrating our LFs we find that the intrinsic ionizing emissivity is dominated by galaxies at all z > 3, and this result holds even after applying a notional escape fraction. We compare our AGN LFs to predictions based on different black-hole seeding models, finding decent agreement on average, but that all models are unable to predict the observed abundance of bright AGNs. We make predictions for the upcoming Euclid and Roman observatories, showing that their respective wide-area surveys should be capable of discovering AGNs to z ~ 8.

Carbon Dioxide is an important tracer of the chemistry and physics in the terrestrial planet forming zone. Using a thermo-chemical model that has been tested against the mid-infrared water emission we re-interpret the CO2 emission as observed with Spitzer. We find that both water UV-shielding and extra chemical heating significantly reduce the total CO2 column in the emitting layer. Water UV-shielding is the more efficient effect, reducing the CO2 column by $\sim$ 2 orders of magnitude. These lower CO2 abundances lead to CO2-to-H2O flux ratios that are closer to the observed values, but CO2 emission is still too bright, especially in relative terms. Invoking the depletion of elemental oxygen outside of the water mid-plane iceline more strongly impacts the CO2 emission than it does the H2O emission, bringing the CO2-to-H2O emission in line with the observed values. We conclude that the CO2 emission observed with Spitzer-IRS is coming from a thin layer in the photo-sphere of the disk, similar to the strong water lines. Below this layer, we expect CO2 not to be present except when replenished by a physical process. This would be visible in the $^{13}$CO2 spectrum as well as certain $^{12}$CO2 features that can be observed by JWST-MIRI.

Pox 186 is an exceptionally small dwarf starburst galaxy hosting a stellar mass of $\sim10^5$ M$_{\odot}$. Undetected in HI (M $ < 10^6$ M$_{\odot}$) from deep 21 cm observations and with an [OIII]/[OII]\ (5007/3727) ratio of 18.3 $\pm$ 0.11, Pox~186 is a promising candidate Lyman continuum emitter. It may be a possible analog of low-mass reionization-era galaxies. We present a spatially resolved kinematic study of Pox 186 and identify two distinct ionized gas components: a broad one with $\sigma > 400$ \kmps, and a narrow one with $\sigma < 30$ \kmps. We find strikingly different morphologies between the two components and direct evidence of outflows as seen in the high velocity gas. Possible physical mechanisms driving the creation of high velocity gas seen in [OIII] are discussed, from outflow geometry to turbulent mixing between a hot (10$^6$ K) star-cluster wind and cooler (10$^4$ K) gas clouds. We find a modest mass-outflow rate of 0.022 M$_{\odot}$ \ yr$^{-1}$ with a small mass loading factor of 0.5, consistent with other low mass galaxies. Finally we compare the mass-loading factor of Pox~186 with extrapolations from numerical simulations and discuss possible reasons for the apparent discrepancy between them.

This chapter outlines the general principles for the detection and characterisation of high-energy $\gamma$-ray photons in the energy range from MeV to GeV. Applications of these fundamental photon-matter interaction processes to the construction of instruments for $\gamma$-ray astronomy are described, including a short review of past and present realisations of telescopes. The constraints encountered in operating telescopes on high-altitude balloon and satellite platforms are described in the context of the strong instrumental background from cosmic rays as well as astrophysical sources. The basic telescope concepts start from the general collimator aperture in the MeV range over its improvements through coded-mask and Compton telescopes, to pair production telescopes in the GeV range. Other apertures as well as understanding the measurement principles of $\gamma$-ray astrophysics from simulations to calibrations are also provided.

We present the first results of a pilot program to conduct an Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (211-275 GHz) spectral line study of young stellar objects (YSO) that are undergoing rapid accretion episodes, i.e. FU Ori objects (FUors). Here, we report on molecular emission line observations of the FUor system, V883 Ori. In order to image the FUor object with full coverage from ~0.5 arcsec to the map size of ~30 arcsec, i.e. from disc to outflow scales, we combine the ALMA main array (the 12-m array) with the Atacama Compact Array (7-m array) and the total power (TP) array. We detect HCN, HCO$^{+}$, CH$_{3}$OH, SO, DCN, and H$_{2}$CO emissions with most of these lines displaying complex kinematics. From PV diagrams, the detected molecules HCN, HCO$^{+}$, CH$_{3}$OH, DCN, SO, and H$_{2}$CO probe a Keplerian rotating disc in a direction perpendicular to the large-scale outflow detected previously with the $^{12}$CO and $^{13}$CO lines. Additionally, HCN and HCO$^{+}$ reveal kinematic signatures of infall motion. The north outflow is seen in HCO$^{+}$, H$_{2}$CO, and SO emissions. Interestingly, HCO$^{+}$ emission reveals a pronounced inner depression or "hole" with a size comparable to the radial extension estimated for the CH$_{3}$OH and 230 GHz continuum. The inner depression in the integrated HCO$^{+}$ intensity distribution of V883 Ori is most likely the result of optical depth effects, wherein the optically thick nature of the HCO$^{+}$ and continuum emission towards the innermost parts of V883 Ori can result in a continuum subtraction artifact in the final HCO$^{+}$ flux level.

In this paper, we discuss atomic processes modifying the soft X-ray spectra in from optical depth effects like photoelectric absorption and electron scattering suppressing the soft X-ray lines. We also show the enhancement in soft X-ray line intensities in a photoionized environment via continuum pumping. We quantify the suppression/enhancement by introducing a "line modification factor ($f_{\rm mod}$)." If 0 $\leq$ $f_{\rm mod}$ $\leq$ 1, the line is suppressed, which could be the case in both collisionally-ionized and photoionized systems. If $f_{\rm mod}$ $\geq$ 1, the line is enhanced, which occurs in photoionized systems. Hybrid astrophysical sources are also very common, where the environment is partly photoionized and partly collisionally-ionized. Such a system is V1223 Sgr, an intermediate polar binary. We show the application of our theory by fitting the first-order Chandra MEG spectrum of V1223 Sgr with a combination of \textsc{Cloudy}-simulated additive cooling-flow and photoionized models. In particular, we account for the excess flux for O~VII, O~VIII, Ne~IX, Ne~X, and Mg~XI lines in the spectrum found in a recent study, which could not be explained with an absorbed cooling-flow model.

MARCOT Pathfinder is a precursor for MARCOT (Multi Array of Combined Telescopes) at Calar Alto Observatory (CAHA) in Spain. MARCOT is intended to provide CARMENES, currently fiber-fed from the CAHA 3.5m Telescope, with a 5-15m light collecting area from a battery of several tens of small telescopes that are incoherently fed into the final joint single fiber feed of the spectrograph. The modular concept, based on commercially available telescopes, results in cost estimates that are a fraction of the ones for extremely large telescopes (ELT). As a novel approach, MARCOT will employ Multi-Mode Photonic Lanterns (MM-PL) that are being developed as a variant of classical photonic lanterns, to combine the light from the individual telescopes to a single fiber feed to the instrument. This progress report presents the overall concept of MARCOT, the pathfinder telescope and enclosure that is being commissioned at CAHA, the concept of MM-PL, and the next step of installing the Potsdam Multiplex Raman Spectrograph (MRS). MARCOT Pathfinder will be used to validate the conceptual design and predicted performance of MM-PL on sky with a 7 unit telescope prototype.

Direct detection of gravitational waves (GW) on Aug. 17, 2017, propagating from a binary neutron star merger, opened the era of multimessenger astronomy. The ejected material from neutron star mergers, or kilonova, is a good candidate for optical and near infrared follow-up observations after the detection of GWs. The kilonova from the ejecta of GW1780817 provided the first evidence for the astrophysical site of the synthesis of heavy nuclei through the rapid neutron capture process or rprocess. Since properties of the emission are largely affected by opacities of the ejected material, enhancements in the available, but limited rprocess atomic data have been motivated recently. However, given the complexity of the electronic structure of these heavy elements, considerable efforts are still needed to converge to a reliable set of atomic structure data. The aim of this work is to alleviate this situation for low charge state elements in the Os-like isoelectronic sequence. In this regard, the general purpose relativistic atomic structure packages (GRASP0 and GRASP2K) were used to obtain energy levels and transition probabilities (E1 and M1). We provide line lists and expansion opacities for a range of r-process elements. We focus here on the Os isoelectronic sequence (Os I, Ir II, Pt III, Au IV, Hg V). The results are benchmarked against existing experimental data and prior calculations, and predictions of emission spectra relevant to kilonovae are provided. Finestructure (M1) lines in the infrared potentially observable by the James Webb Space Telescope are highlighted.

Understanding if and when the accretion disc extends down to the innermost stable circular orbit (ISCO) is important since it is the fundamental assumption behind measuring black hole spin. Here, we examine the 2013 and 2018 NuSTAR and Swift data (0.5 - 50 keV) of the narrow-line Seyfert 1 galaxy, WKK 4438. The X-ray emission can be fitted well with models depicting a corona and blurred reflection originating from a disc around a low spin (a* ~ 0) black hole. However, such models result in unconventional values for some of the parameters (e.g. inverted emissivity profile and high coronal height). Alternatively, equally good fits can be achieved if the disc is truncated at ~10 rg and the black hole is spinning at the Thorne limit (a* = 0.998). In these cases, the model parameters are consistent with the interpretation that the corona is centrally located close to the black hole and illuminating the disc at a larger distance.

Young stars show variability on different time-scales from hours to decades, with a range of amplitudes. We studied two young stars, which triggered the Gaia Science Alerts system due to brightenings on a time-scale of a year. Gaia20bwa brightened by about half a magnitude, whereas Gaia20fgx brightened by about two and half magnitudes. We analyzed the Gaia light curves, additional photometry, and spectra taken with the Telescopio Nazionale Galileo and the Gran Telescopio Canarias. Several emission lines were detected toward Gaia20bwa, including hydrogen lines from H$\alpha$ to H$\delta$, Pa$\beta$, Br$\gamma$, and lines of Ca II, O I, and Na I. The H$\alpha$ and Br$\gamma$ lines were detected toward Gaia20fgx in emission in its bright state, with additional CO lines in absorption, and the Pa$\beta$ line with an inverse P Cygni profile during its fading. Based on the Br$\gamma$ lines the accretion rate was $(2.4-3.1)\times10^{-8}$ $M_\odot$ yr$^{-1}$ for Gaia20bwa and $(4.5-6.6)\times10^{-8}$ $M_\odot$ yr$^{-1}$ for Gaia20fgx during their bright state. The accretion rate of Gaia20fgx dropped by almost a factor of 10 on a time-scale of half a year. The accretion parameters of both stars were found to be similar to those of classical T Tauri stars, lower than those of young eruptive stars. However, the amplitude and time-scale of these brightenings place these stars to a region of the parameter space, which is rarely populated by young stars. This suggests a new class of young stars, which produce outbursts on a time-scale similar to young eruptive stars, but with smaller amplitudes.

We employ Gaia, 2MASS, and ALLWISE photometry, as well as astrometric data from Gaia, to search for relatively bright very metal-poor ([Fe/H] $< -2.0$; VMP) giant star candidates using three different criteria: 1) our derived Gaia photometric metallicities, 2) the lack of stellar molecular absorption near 4.6 microns, and 3) their high tangential velocities. With different combinations of these criteria, we have identified six samples of candidates with $G <$ 15: the Gold sample (24,304 candidates), the Silver GW sample (40,157 candidates), the Silver GK sample (120,452 candidates), the Bronze G sample (291,690 candidates), the Bronze WK sample (68,526 candidates), and the Low $b$ sample (4,645 candidates). The Low $b$ sample applies to sources with low Galactic lattitude, $|b| < 10^\circ$, while the others are for sources with $|b| > 10^\circ$. By cross-matching with results derived from medium-resolution ($R \sim$ 1800) from LAMOST DR8, we establish that the success rate for identifying VMP stars is 60.1$\%$ for the Gold sample, 39.2$\%$ for the Silver GW sample, 41.3$\%$ for the Silver GK sample, 15.4$\%$ for the Bronze G sample, 31.7$\%$ for the Bronze WK sample, and 16.6$\%$ for the Low $b$ sample, respectively. An additional strict cut on the quality parameter $RUWE < 1.1$ can further increase the success rate of the Silver GW, Silver GK, and Bronze G samples to 46.9$\%$, 51.6$\%$, and 29.3$\%$, respectively. Our samples provide valuable targets for high-resolution follow-up spectroscopic observations, and are made publicly available.

Recent local measurements of the Hubble constant made using supernovae have delivered a value that differs by $\sim$5$\sigma$ (statistical error) from predictions using the Cosmic Microwave Background (CMB), or using Baryon Acoustic Oscillations (BAO) and Big-Bang Nucleosynthesis (BBN) constraints, which are themselves consistent. The effective volume covered by the supernovae is small compared to the other probes, and it is therefore interesting to consider whether sample variance (often also called cosmic variance) is a significant contributor to the offset. We consider four ways of calculating the sample variance: (i) perturbation theory applied to the luminosity distance, which is the most common method considered in the literature; (ii) perturbation of cosmological parameters, as is commonly used to alleviate super-sample covariance in sets of N-body simulations; (iii) a new method based on the variance between perturbed spherical top-hat regions; (iv) using numerical N-body simulations. All give consistent results showing that, for the Pantheon supernova sample, sample variance can only lead to fluctuations in $H_0$ of order $\pm1$ km s$^{-1}$Mpc$^{-1}$ or less. While this is not in itself a new result, the agreement between the methods used adds to its robustness. Furthermore, it is instructive to see how the different methods fit together. We also investigate the internal variance of the $H_{0}$ measurement using SH0ES and Pantheon data. By searching for an offset between measurements in opposite hemispheres, we find that the direction coincident with the CMB dipole has a higher $H_{0}$ measurement than the opposite hemisphere by roughly 4 km s$^{-1}$Mpc$^{-1}$. We compare this with a large number of simulations and find that the size of this asymmetry is statistically likely, but the preference of direction may indicate that further calibration is needed.

A recent study conducted using CALIFA survey data (Lee et al, 2019b) has found that the orbital motions of neighbor galaxies are coherent with the spin direction of a target galaxy on scales of many Megaparsecs. We study this so called `large-scale coherence' phenomena using N-body cosmological simulations. We confirm a strong coherence signal within 1 Mpc/h of a target galaxy, reaching out to 6 Mpc/h. We divide the simulation halos into subsamples based on mass, spin, merger history and local halo number density for both target and neighbor halos. We find a clear dependency on the mass of the target halo only. Another key parameter was the local number density of both target and neighbor halos, with high density regions such as clusters and groups providing the strongest coherence signals, rather than filaments or lower density regions. However we do not find a clear dependency on halo spin or time since last major merger. The most striking result we find is that the signal can be detected up to~15Mpc/h from massive halos. These result provide valuable lessons for how observational studies could more clearly detect coherence, and we discuss the implications of our results for the origins of large-scale coherence.

Mass loss remains a major uncertainty in stellar modelling. In low-mass stars, mass loss is most significant on the red giant branch (RGB), and will impact the star's evolutionary path and final stellar remnant. Directly measuring the mass difference of stars in various phases of evolution represents one of the best ways to quantify integrated mass loss. Globular clusters (GCs) are ideal objects for this. M4 is currently the only GC for which asteroseismic data exists for stars in multiple phases of evolution. Using K2 photometry, we report asteroseismic masses for 75 red giants in M4, the largest seismic sample in a GC to date. We find an integrated RGB mass loss of $\Delta\bar{M} = 0.17 \pm 0.01 ~\mathrm{M}_{\odot}$, equivalent to a Reimers' mass-loss coefficient of $\eta_R = 0.39$. Our results for initial mass, horizontal branch mass, $\eta_R$, and integrated RGB mass loss show remarkable agreement with previous studies, but with higher precision using asteroseismology. We also report the first detections of solar-like oscillations in early asymptotic giant branch (EAGB) stars in GCs. We find an average mass of $\bar{M}_{\text{EAGB}}=0.54 \pm 0.01 ~\mathrm{M}_{\odot}$, significantly lower than predicted by models. This suggests larger-than-expected mass loss on the horizontal branch. Alternatively, it could indicate unknown systematics in seismic scaling relations for the EAGB. We discover a tentative mass bi-modality in the RGB sample, possibly due to the multiple populations. In our red horizontal branch sample, we find a mass distribution consistent with a single value. We emphasise the importance of seismic studies of GCs since they could potentially resolve major uncertainties in stellar theory.

The tidal properties of a neutron star are measurable in the gravitational waves emitted from inspiraling binary neutron stars, and they have been used to constrain the neutron star equation of state. In the same spirit, we study the dimensionless tidal deformability of dark matter admixed neutron stars. The tidal Love number is computed in a two-fluid framework. The dimensionless tidal Love number and dimensionless tidal deformability are computed for dark matter admixed stars with the dark matter modelled as ideal Fermi gas or self-interactive bosons. The dimensionless tidal deformability shows a sharp change from being similar to that of a pure normal matter star to that of a pure dark matter star, within a narrow range of intermediate dark matter mass fraction. Based on this result, we illustrate an approach to study the dark matter parameters through the tidal properties of massive compact stars, making use of the self-similarity of the dimensionless tidal deformability-mass relations when the dark matter mass fraction is high.

In this article, we have done a thorough investigation of the possible effects of interaction between dark matter (DM) and neutrinos on reionization history. We have constrained the interaction strength using 21 cm Cosmology and found out possible deviations from standard, non-interacting $\Lambda$CDM scenario. Comparing the results with the existing constraints from present cosmological observations reveals that 21 cm observations are more competent to constrain the interaction strength by a few orders of magnitude. We have also searched for prospects of detecting any such interaction in the upcoming 21 cm mission SKA1-Low by doing a forecast analysis and error estimation.

We present a revised analysis of the photometric reverberation mapping campaign of the narrow-line Seyfert 1 galaxy PKS 0558-504 carried out with the Swift Observatory during 2008--2010. Previously, Gliozzi et al.\ found using the Discrete Correlation Function (DCF) method that the short-wavelength continuum variations lagged behind variations at longer wavelengths, the opposite of the trend expected for thermal reprocessing of X-rays by the accretion disc, and they interpreted their results as evidence against the reprocessing model. We carried out new DCF measurements that demonstrate that the inverted lag-wavelength relationship found by Gliozzi et al.\ resulted from their having interchanged the order of the driving and responding light curves when measuring the lags. To determine the inter-band lags and uncertainties more accurately, we carried out new measurements with four independent methods. These give consistent results showing time delays increasing as a function of wavelength, as expected for the disc reprocessing scenario. The slope of the re-analysed delay spectrum appears to be roughly compatible with the predicted $\tau \propto \lambda^{4/3}$ relationship for reprocessing by an optically thick and geometrically thin accretion disc, although the data points exhibit a large scatter about the fitted power-law trend.

Context: Statistical properties of the cosmic density fields are to a large extent encoded in the shape of the one-point density probability distribution functions (PDF). In order to successfully exploit such observables, a detailed functional form of the covariance matrix of the one-point PDF is needed. Aims: The objectives are to model the properties of this covariance for general stochastic density fields in a cosmological context. Methods: Leading and subleading contributions to the covariance were identified within a large class of models, the so-called hierarchical models. The validity of the proposed forms for the covariance matrix was assessed with the help of a toy model, the minimum tree model, for which a corpus of exact results could be obtained (forms of the one- and two-point PDF, large-scale density-bias functions, and full covariance matrix of the one-point PDF). Results: It is first shown that the covariance matrix elements are directly related to the spatial average of the two-point density PDF within the sample. The dominant contribution to this average is explicitly given for hierarchical models, which leads to the construction of specific density-bias functions. However, this contribution alone cannot be used to construct an operational likelihood function. Short distance effects are found to be have an important impact but are more difficult to derive as they depend more on the details of the model. However, a simple and generic form of these contributions is proposed. Detailed comparisons in the context of the Rayleigh-Levy flight model show that the large-scale effects capture the bulk of the supersample effects and that, by adding the short-distance contributions, a qualitatively correct model of the likelihood function can be obtained.

The origin of organic compounds detected in meteorites and comets, some of which could serve as precursors of life on Earth, still remains an open question. The aim of the present study is to make one more step in revealing the nature and composition of organic materials of extraterrestrial particles by comparing infrared spectra of laboratory-made refractory organic residues to the spectra of cometary particles returned by the Stardust mission, interplanetary dust particles, and meteorites. Our results reinforce the idea of a pathway for the formation of refractory organics through energetic and thermal processing of molecular ices in the solar nebula. There is also the possibility that some of the organic material formed already in the parental molecular cloud before it entered the solar nebula. The majority of the IR "organic" bands of the studied extraterrestrial particles can be reproduced in the spectra of the laboratory organic residues. We confirm the detection of water, nitriles, hydrocarbons, and carbonates in extraterrestrial particles and link it to the formation location of the particles in the outer regions of the solar nebula. To clarify the genesis of the species, high-sensitivity observations in combination with laboratory measurements like those presented in this paper are needed. Thus, this study presents one more piece of the puzzle of the origin of water and organic compounds on Earth and motivation for future collaborative laboratory and observational projects.

By performing two-dimensional axisymmetric general relativistic radiation magnetohydrodynamics simulations with spin parameter $a^*$ varying from -0.9 to 0.9, we investigate the dependence on the black hole spin of the energy flow from supercritical accretion disk around stellar mass black hole. It is found that optically and geometrically thick disks form near the equatorial plane, and a part of the disk matter is launched from the disk surface in all models. The gas ejection is mainly driven by the radiative force, but magnetic force cannot be neglected, when $|a^*|$ is large. The energy outflow efficiency (total luminosity normalized by $\dot{M}_{\rm in} c^2 $; $\dot{M}_{\rm in}$ and $c$ are the mass accretion rate at the event horizon and the light speed) is larger for rotating black holes than for non-rotating black holes. This is $0.7\%$ for $a^*=-0.7$, $0.3\%$ for $a^*=0$, and $5\%$ for $a^*=0.7$ for $\dot{M}_{\rm in} \sim 100L_{\rm Edd}/c^2$ ($L_{\rm Edd}$ is Eddington luminosity). Also, although the energy is mainly released by radiation when $a^* \sim 0$, the Poynting power increases with $|a^*|$ and exceeds the radiative luminosity for models with $a^* \geq 0.5$ and $a^* \leq -0.7$. The more the black hole rotates, the larger the power ratio of the kinetic luminosity to the isotropic luminosity tends to be. This implies that objects with large (small) power ratio may have rapidly (slowly) rotating black holes. Among ultraluminous X-ray sources, IC342 X-1, is a candidate with a rapidly rotating black hole.

In this work we investigate the possibility of constraining a thawing Quintessence scalar field model for dark energy. We propose using the imprint of baryon acoustic oscillation (BAO) on the cross-correlation of post-reionization 21-cm signal and galaxy weak lensing convergence field to tomographically measure the angular diameter distance $D_A(z)$ and the Hubble parameter $H(z)$. The projected errors in these quantities are then used to constrain the Quintessence model parameters. We find that independent $600$hrs radio interferometric observation at four observing frequencies $916 $MHz, $650$ MHz, $520$ MHz and $430 $MHz with a SKA-1-Mid like radio telescope in cross-correlation with a deep weak lensing survey covering half the sky may measure the binned $D_A$ and $H$ at a few percent level of sensitivity. The Monte Carlo analysis for a power law thawing Quintessence model gives the $1-\sigma$ marginalized bounds on the initial slope $\lambda_i$,dark energy density parameter $\Omega_{\phi 0}$ and the shape of the potential $\Gamma$ at 8.63%, 10.08% and 9.75% respectively. The constraints improve to 7.66%, 4.39% and 5.86% respectively when a joint analysis with SN and other probes is performed.

The differential refraction of light passing through the atmosphere can have a severe impact on image quality if no atmospheric dispersion corrector (ADC) is used. For the Extremely Large Telescope (ELT) this holds true well into the infrared. MICADO, the near-infrared imaging camera for the ELT, will employ a cryogenic ADC consisting of two counter-rotating Amici prisms with diameters of 125 mm. The mechanism will reduce the atmospheric dispersion to below 2.5 milli arcseconds (mas), with a set goal of 1 mas. In this report, we provide an overview of the current status of the ADC in development for MICADO. We summarise the optomechanical design and discuss how the cryogenic environment impacts the performance. We will also discuss our plan to use a diffraction mask in the cold pupil to calibrate and validate the performance once the instrument is fully integrated.

The origin of Galactic Cosmic Rays (CRs) and the possibility of Supernova Remnants (SNRs) being potential CR accelerators is still an open debate. The charged CRs can be detected indirectly by the {\gamma}-ray observatories through the {\pi^0} production and consequent decay, leading to the generation of high-energy {\gamma}-rays. The goal of the study is to identify qualitative and quantitative trends in favour of hadronic scenario and search for SNRs which could be potential accelerators up to PeV energies (PeVatrons). We have performed a Multiwavelength (MWL) study using different radiative models to evaluate the hadronic contribution. The spectral energy distributions (SEDs) of selected SNRs are modeled using the Naima [1] package. Two different radiative scenarios are considered, pure leptonic and lepto-hadronic scenarios, and different methods are used to evaluate their importance. This study shows that the lepto-hadronic scenario is favored for most SNRs. Two particular indicators of hadronic contribution come from the data around the {\pi^0} production threshold and the data above a few TeV. The hard rise at the {\pi^0} production threshold cannot be explained by leptonic processes. More data in this region would be valuable for these studies. For some SNRs, an important hadronic contribution is observed up to a few TeV, thus making them promising PeVatron candidates. In this high-energy region where the leptonic processes are expected to be suppressed, more data is required to help distinguish between the leptonic and hadronic origin of {\gamma}-ray emission. In the future, we intend to use the obtained model parameters to simulate data for CTA and assess its capability to identify PeVatrons.

The Aryabhatta Research Institute of Observational Sciences (ARIES), a premier autonomous research institute under the Department of Science and Technology, Government of India has a legacy of about seven decades with contributions made in the field of observational sciences namely atmospheric and astrophysics. The Survey of India used a location at ARIES, determined with an accuracy of better than 10 meters on a world datum through institute participation in a global network of Earth artificial satellites imaging during late 1950. Taking advantage of its high-altitude location, ARIES, for the first time, provided valuable input for climate change studies by long term characterization of physical and chemical properties of aerosols and trace gases in the central Himalayan regions. In astrophysical sciences, the institute has contributed precise and sometime unique observations of the celestial bodies leading to a number of discoveries. With the installation of the 3.6 meter Devasthal optical telescope in the year 2015, India became the only Asian country to join those few nations of the world who are hosting 4 meter class optical telescopes. This telescope, having advantage of geographical location, is well-suited for multi-wavelength observations and for sub-arc-second resolution imaging of the celestial objects including follow-up of the GMRT, AstroSat and gravitational-wave sources.

I analyze some properties of the luminous transient event SN 2019zrk and conclude that jets were the main powering sources of the pre-explosion outburst (pre-cursor) and ejection of a massive circumstellar matter (CSM), of the very energetic explosion itself, and of the post-explosion bump in the light curve. The pre-explosion energy source is mainly a companion (main sequence, Wolf-Rayet, neutron star or black hole) star that accreted mass and launched jets. I find that the fast expansion of the CSM after acceleration by the explosion ejecta requires the explosion energy to be >10^{52}erg. Only jet-driven explosions can supply this energy in such SN 2009ip-like transients. I conclude that ejecta-CSM interaction is extremely unlikely to power the bright bump at about 110 days after explosion. Instead, I show by applying a jet-driven bump toy-model that post-explosion jets are the most likely explanation for the bump. I leave open the question of whether the explosion itself (main outburst) was a core collapse supernova (CCSN) or a common envelope jets supernova (CEJSN). In this study I further connect peculiar transient events, here 2009ip-like transient events, to CCSNe by arguing that jets drive all events, from regular CCSNe through superluminous CCSNe and to many other peculiar and super-energetic transient events, including CEJSNe. Jet-powering cannot be ignored when analyzing all these types of transients.

Astrophysical light curves are particularly challenging data objects due to the intensity and variety of noise contaminating them. Yet, despite the astronomical volumes of light curves available, the majority of algorithms used to process them are still operating on a per-sample basis. To remedy this, we propose a simple Transformer model -- called Denoising Time Series Transformer (DTST) -- and show that it excels at removing the noise and outliers in datasets of time series when trained with a masked objective, even when no clean targets are available. Moreover, the use of self-attention enables rich and illustrative queries into the learned representations. We present experiments on real stellar light curves from the Transiting Exoplanet Space Satellite (TESS), showing advantages of our approach compared to traditional denoising techniques.

Chemical composition is an important factor that affects stellar evolution. The element abundance on the stellar surface evolves along the lifetime of the star because of transport processes, including atomic diffusion. However, models of stars with masses higher than about 1.2Msun predict unrealistic variations at the stellar surface. This indicates the need for competing transport processes that are mostly computationally expensive for large grids of stellar models. The purpose of this study is to implement turbulent mixing in stellar models and assess the possibility of reproducing the effect of radiative accelerations with turbulent mixing for elements like iron in order to make the computation of large grids possible. We computed stellar models with MESA and assessed the effects of atomic diffusion (with radiative acceleration) in the presence of turbulent mixing. We parametrised the effect of radiative accelerations on iron with a turbulent diffusion coefficient. Finally, we tested this parametrisation by modelling two F-type stars of the Kepler Legacy sample. We found that, for iron, a parametrisation of turbulent mixing that simulates the effect of radiative acceleration is possible. This leads to an increase in the efficiency of the turbulent mixing to counteract the effect of gravitational settling. This approximation does not affect significantly the surface abundances of the other elements we studied, except for oxygen and calcium. We demonstrate that this parametrisation has a negligible impact on the accuracy of the seismic properties inferred with these models. Moreover, turbulent mixing makes the computation of realistic F-type star models including the effect atomic diffusion possible. This leads to differences of about 10% in the inferred ages compared to results obtained with models that neglect these processes.

Stellar spectra encode detailed information about the stars. However, most machine learning approaches in stellar spectroscopy focus on supervised learning. We introduce Mendis, an unsupervised learning method, which adopts normalizing flows consisting of Neural Spline Flows and GLOW to describe the complex distribution of spectral space. A key advantage of Mendis is that we can describe the conditional distribution of spectra, conditioning on stellar parameters, to unveil the underlying structures of the spectra further. In particular, our study demonstrates that Mendis can robustly capture the pixel correlations in the spectra leading to the possibility of detecting unknown atomic transitions from stellar spectra. The probabilistic nature of Mendis also enables a rigorous determination of outliers in extensive spectroscopic surveys without the need to measure elemental abundances through existing analysis pipelines beforehand.

A key yet unresolved question in modern-day astronomy is how galaxies formed and evolved under the paradigm of the $\Lambda$CDM model. A critical limiting factor lies in the lack of robust tools to describe the merger history through a statistical model. In this work, we employ a generative graph network, E(n) Equivariant Graph Normalizing Flows Model. We demonstrate that, by treating the progenitors as a graph, our model robustly recovers their distributions, including their masses, merging redshifts and pairwise distances at redshift z=2 conditioned on their z=0 properties. The generative nature of the model enables other downstream tasks, including likelihood-free inference, detecting anomalies and identifying subtle correlations of progenitor features.

We introduce Astroconformer, a Transformer-based model to analyze stellar light curves from the Kepler mission. We demonstrate that Astrconformer can robustly infer the stellar surface gravity as a supervised task. Importantly, as Transformer captures long-range information in the time series, it outperforms the state-of-the-art data-driven method in the field, and the critical role of self-attention is proved through ablation experiments. Furthermore, the attention map from Astroconformer exemplifies the long-range correlation information learned by the model, leading to a more interpretable deep learning approach for asteroseismology. Besides data from Kepler, we also show that the method can generalize to sparse cadence light curves from the Rubin Observatory, paving the way for the new era of asteroseismology, harnessing information from long-cadence ground-based observations.

Modeling quasar spectra is a fundamental task in astrophysics as quasars are the tell-tale sign of cosmic evolution. We introduce a novel unsupervised learning algorithm, Quasar Factor Analysis (QFA), for recovering the intrinsic quasar continua from noisy quasar spectra. QFA assumes that the Ly$\alpha$ forest can be approximated as a Gaussian process, and the continuum can be well described as a latent factor model. We show that QFA can learn, through unsupervised learning and directly from the quasar spectra, the quasar continua and Ly$\alpha$ forest simultaneously. Compared to previous methods, QFA achieves state-of-the-art performance for quasar continuum prediction robustly but without the need for predefined training continua. In addition, the generative and probabilistic nature of QFA paves the way to understanding the evolution of black holes as well as performing out-of-distribution detection and other Bayesian downstream inferences.

Context: Stellar evolution models are highly dependent on accurate mass estimates, especially for high-mass stars in the early stages of evolution. The most direct method for obtaining model-independent masses is derivation from the orbit of close binaries. Aims: To derive the first astrometric+RV orbit solution for the single-lined spectroscopic binary MWC 166 A, based on CHARA and VLTI near-infrared interferometry over multiple epochs and ~100 archival radial velocity measurements, and to derive fundamental stellar parameters from this orbit. We also sought to model circumstellar activity in the system from K-band spectral lines. Methods: We geometrically modelled the dust continuum to derive astrometry at 13 epochs and constrain individual stellar parameters. We used the continuum models as a base to examine differential phases, visibilities and closure phases over the Br-$\gamma$ and He-I emission lines. Results: Our orbit solution suggests a period of $367.7\pm0.1$ d, twice as long as found with previous RV orbit fits, subsequently constraining the component masses to $M_1=12.2\pm2.2 M_\odot$ and $M_2=4.9\pm0.5 M_\odot$. The line-emitting gas was found to be localised around the primary and is spatially resolved on scales of ~11 stellar radii, with the spatial displacement between the line wings consistent with a rotating disc. Conclusions: The large radius and stable orientation of the line emission are inconsistent with magnetospheric or boundary-layer accretion, but indicate an ionised inner gas disk around MWC 166 Aa. We observe line variability that could be explained either with generic line variability in a Herbig star disc or V/R variations in a decretion disc. We also constrained the age of the system to ~$(7\pm2)\times10^5$ yr, consistent with the system being comprised of a main-sequence primary and a secondary still contracting towards the main sequence.

Solar flares release an enormous amount of energy in the corona. A substantial fraction of this energy is transported to the lower atmosphere, which results in chromospheric heating. The mechanisms that transport energy to the lower solar atmosphere during a flare are still not fully understood. We aim to estimate the temporal evolution of the radiative losses in the chromosphere at the footpoints of a C-class flare, in order to set observational constraints on the electron beam parameters of a RADYN flare simulation. We estimated the radiative losses from hydrogen, and singly ionized Ca and Mg using semi-empirical model atmospheres. To estimate the integrated radiative losses in the chromosphere the net cooling rates were integrated between the temperature minimum and the height where the temperature reaches 10 kK. The stratification of the net cooling rate suggests that the Ca IR triplet lines are responsible for most of the radiative losses in the flaring atmosphere. During the flare peak time, the contribution from Ca II H & K and Mg II h & k lines are strong and comparable to the Ca IR triplet ($\sim$32 kW m$^{-2}$). Since our flare is a relatively weak event the chromosphere is not heated above 11 kK, which in turn yields a subdued Ly{\alpha} contribution ($\sim$7 kW m$^{-2}$). The temporal evolution of total integrated radiative losses exhibits sharply-rising losses (0.4 kW m$^{-2}$ s$^{-1}$) and a relatively slow decay (0.23 kW~m$^{-2}$ s$^{-1}$). The maximum value of total radiative losses is reached around the flare peak time, and can go up to 175 kW m$^{-2}$ for a single pixel located at footpoint. After a small parameter study, we find the best model-data consistency in terms of the amplitude of radiative losses and the overall atmospheric structure with a RADYN flare simulation in the injected energy flux of $5\times10^{10}$ erg s$^{-1}$ cm$^{-2}$.

The flavor evolution of neutrinos in core collapse supernovae and neutron star mergers is a critically important unsolved problem in astrophysics. Following the electron flavor evolution of the neutrino system is essential for calculating the thermodynamics of compact objects as well as the chemical elements they produce. Accurately accounting for flavor transformation in these environments is challenging for a number of reasons, including the large number of neutrinos involved, the small spatial scale of the oscillation, and the nonlinearity of the system. We take a step in addressing these issues by presenting a method which describes the neutrino fields in terms of angular moments. Our moment method successfully describes the fast flavor neutrino transformation phenomenon which is expected to occur in regions close to the central object. We apply our moment method to neutron star merger conditions and show that we are able to capture the three phases of growth, saturation, and decoherence by comparing with particle-in-cell calculations. We also determine the size of the growing fluctuations in the neutrino field.

Scattering interactions between dark matter and Standard Model states mediated by pseudoscalars are generically challenging to uncover at direct detection experiments due to rates suppressed by powers of the local dark matter velocity v ~ 0.001 c. However, they may be observed in the dark matter-induced heating of neutron stars, whose steep gravitational potentials prevent such suppression by accelerating infalling particles to semi-relativistic speeds. We investigate this phenomenon in the context of two specific, self-consistent scenarios for pseudoscalars coupled to dark matter, and compare the sensitivity of neutron star heating to bounds from direct searches for the mediators and dark matter. The first "lighter" scenario consists of sub-10 GeV mass dark matter mediated by an axion-like particle (ALP), while the second "heavier" scenario has dark matter above 10 GeV mediated by a dark pseudoscalar that mixes with a pseudoscalar from a two-Higgs doublet (the so-called 2HDM+a model). In both frameworks, we show that imminent measurements of neutron stars will be able to test pseudoscalar-mediated dark matter beyond the reach of direct dark matter searches as well as bounds on the mediators from flavor observables, beam dump experiments, and high-energy colliders.

In light of the exciting campaign of cosmogenic neutrino detection, we investigate the double and multiple tau bangs detectable at future tau neutrino telescopes. Such events are expected from the Standard Model (SM) higher-order processes, which can be easily identified with broad techniques anticipated at future tau neutrino telescopes. We find that SM perturbative processes can already contribute several double-bang events to telescopes with a sensitivity of collecting $\mathcal{O}(300)$ cosmogenic neutrino events. The detectable but suppressed rate in fact makes the double and multiple bangs an excellent probe of SM unknowns and possible new physics beyond. As a case study, the nonperturbative sphaleron process, which can copiously produce multiple tau bangs, is explored.

We analyze the phase transitions in the minimal extension of the SM with a real singlet scalar field. The novelty of our study is that we identify and analyze in details the region of parameter space where the first order phase transition can occur and in particular when the bubbles with true vacuum can reach relativistic velocities. This region is interesting since it can lead to the new recently discussed baryogenesis and Dark Matter production mechanisms. We fully analyze different models for the production of Dark Matter and baryogenesis as well as the possibilities of discovery at the current and future experiments.

Motivated by the fact that cosmological models based on $f(Q)$ gravity are very efficient in fitting observational datasets at both background and perturbation levels, we perform a combined dynamical system analysis of both background and perturbation equations in order to examine the validity of this result through an independent method. We examine two studied $f(Q)$ models of the literature, namely the power-law and the exponential ones. For both cases, we obtain a matter-dominated saddle point characterized by the correct growth rate of matter perturbations, followed by the transition to a stable dark-energy dominated accelerated universe in which matter perturbations remain constant. Furthermore, analyzing the behavior of $f \sigma_8$, we find that the models fit observational data successfully, obtaining a behavior similar to that of $\Lambda$CDM scenario, although the exponential model does not possess the latter as a particular limit. Hence, through the independent approach of dynamical systems, we do verify the results of observational confrontation, namely that $f(Q)$ gravity can be considered as a very promising alternative to the $\Lambda$CDM concordance model.

A Kibble balance measures the $gravitational$ mass (weight) of a test mass with extreme precision by balancing the gravitational pull on the test mass against the electromagnetic lift force. The uncertainty in such mass measurement is currently ~$1\times 10^{-8} $. We show how the same Kibble balance can be used to measure the $inertial$ mass of a test mass, that too with potentially 50% better measurement uncertainty, i.e., ~$5\times 10^{-9} $. For measuring the inertial mass, the weight of the test mass and the assembly holding it is precisely balanced by a counterweight. The application of the known electromagnetic force accelerates the test mass. Measuring the velocity after a controlled elapsed time provides the acceleration and consequently the inertial mass of the accelerated assembly comprising the Kibble balance coil and the mass holding pan. Repeating the measurement with the test mass added to the assembly and taking the difference between the two measurements yields the inertial mass of the test mass. Thus, the extreme precision inertial and gravitational mass measurement of a test mass with a Kibble balance could provide a test of the equivalence principle. We discuss how the two masses are related to the Planck constant and other coupling constants and how the Kibble balance could be used to test the dynamic constants theories in Dirac cosmology.

We introduce $\texttt{GWFAST}$, a novel Fisher-matrix code for gravitational-wave studies, tuned toward third-generation gravitational-wave detectors such as Einstein Telescope (ET) and Cosmic Explorer (CE). We use it to perform a comprehensive study of the capabilities of ET alone, and of a network made by ET and two CE detectors, as well as to provide forecasts for the forthcoming O4 run of the LVK collaboration. We consider binary neutron stars, binary black holes and neutron star-black hole binaries, and compute basic metrics such as the distribution of signal-to-noise ratio (SNR), the accuracy in the reconstruction of various parameters (including distance, sky localization, masses, spins and, for neutron stars, tidal deformabilities), and the redshift distribution of the detections for different thresholds in SNR and different levels of accuracy in localization and distance measurement. We examine the expected distribution and properties of `golden events', with especially large values of the SNR. We also pay special attention to the dependence of the results on astrophysical uncertainties and on various technical details (such as choice of waveforms, or the threshold in SNR), and we compare with other Fisher codes in the literature. In a companion paper we discuss the technical aspects of the code. Together with this paper, we publicly release the code $\texttt{GWFAST}$ at https://github.com/CosmoStatGW/gwfast, and the library $\texttt{WF4Py}$ implementing state-of-the-art gravitational-wave waveforms in pure $\texttt{Python}$ at https://github.com/CosmoStatGW/WF4Py.

Scalar-tensor theories of gravity provide mathematically equivalent descriptions of Einstein's gravity with a scalar field, in a conformally connected spacetime, described in terms of the Jordan frame and the Einstein frame. In this paper, we use the Jordan frame-Einstein frame correspondence to explore dual universes with contrasting cosmological evolutions. We study the mapping between Einstein and Jordan frames where the Einstein frame universe effectively describes the late-time evolution of the physical universe, driven by dark energy and non-relativistic matter. The Brans-Dicke theory of gravity is taken to be the dual scalar-tensor theory in the Jordan frame. We show that the standard Einstein frame universe, with dark energy and non-relativistic matter, always corresponds to a bouncing Jordan frame universe, if it is governed by a Brans-Dicke theory. This essentially leads to an alternative description of the late-time evolution of the physical universe, in terms of a bouncing Brans-Dicke universe in the Jordan frame. Previous studies have shown that for a bouncing Jordan frame, particularly for an early-time accelerating phase of the universe, the map between the Einstein and Jordan frames may become singular in the perturbative regime, causing the conformal correspondence to break down. In order to check whether the present bouncing model for late-time acceleration is free of such instabilities, we study the evolution of scalar metric perturbations. The Jordan frame metric perturbations are numerically solved, first via the Einstein frame using the conformal correspondence, and then directly in the Jordan frame. The evolutions of perturbations obtained in these two cases are in a good agreement. Thus, the duality between the Einstein frame, mimicking the physical universe, and the bouncing Brans-Dicke Jordan frame, is shown to be stable against linear perturbations.