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Turbulence influences the structure and dynamics of molecular clouds, and plays a key role in regulating star formation. We therefore need methods to accurately infer turbulence properties of molecular clouds from position-position-velocity (PPV) spectral observations. A previous method calibrated with simulation data exists to recover the 3D turbulent velocity dispersion from PPV data. However, that method relies on optically-thin conditions, ignoring any radiative transfer (RT) and chemical effects. In the present study we determine how opacity, RT, and chemical effects influence turbulence measurements with CO lines. We post-process a chemo-dynamical simulation of a turbulent collapsing cloud with a non-local thermodynamic equilibrium line RT code to generate PPV spectral cubes of the CO (1-0) and CO (2-1) lines, and obtain moment maps. We isolate the turbulence in the first-moment maps by using a Gaussian smoothing approach. We compare the CO results with the optically-thin scenario to explore how line excitation and RT impact the turbulence measurements. We find that the turbulent velocity dispersion (sigma_v) measured via CO requires a correction by a factor R_CO, with R_CO,1-0 = 0.88 (+0.09, -0.08) for the CO (1-0) line and R_CO,2-1 = 0.88 (+0.10, -0.08) for the CO (2-1) line. As a consequence, previous measurements of sigma_v were overestimated by about 10-15% on average, with potential overestimates as high as 40%, taking the 1-sigma uncertainty into account.

Infrared Dark Clouds (IRDCs) are cold, dense structures representative of the initial conditions of star formation. Many studies of IRDCs employ CO to investigate cloud dynamics. However, CO can be highly depleted from the gas phase in IRDCs, impacting its fidelity as tracer. CO depletion is also of great interest in astrochemistry, since CO ice in dust grain mantles provides the raw material for forming complex organic molecules. We study CO depletion toward four IRDCs to investigate how it correlates with volume density and dust temperature, calculated from Herschel images. We use 13CO(1-0) and (2-1) maps to measure CO depletion factor, $f_D$, across IRDCs G23.46-00.53, G24.49-00.70, G24.94-00.15, and G25.16-00.28. We also consider a normalized CO depletion factor, f_D', which takes a value of unity, i.e., no depletion, in the outer, lower density, warmer regions. We then investigate the dependence of f_D and f_D' on gas density, $n_H$ and dust temperature, $T_{dust}$. We find CO depletion rises as density increases, reaching maximum values of f_D'$\sim$10 in regions with $n_H>3\times10^5\:{cm}^{-3}$, although with significant scatter at a given density. We find a tighter, less scattered relation of f_D' with temperature, rising rapidly for temperatures <18 K. We propose a functional form $f_D^\prime = \:{exp}(T_0/[T_{dust}-T_1])$ with $T_0\simeq4\:$K and $T_1\simeq12\:$K to reproduce this behaviour. We conclude that CO is heavily depleted from the gas phase in cold, dense regions of IRDCs. Thus CO depletion can lead to underestimation of total cloud masses based on CO line fluxes by factors up to 5. These results indicate a dominant role for thermal desorption in setting near equilibrium abundances of gas phase CO in IRDCs, providing important constraints for both astrochemical models and the chemodynamical history of gas during the early stages of star formation.

We analyze an ensemble of simulated prestellar cores to facilitate interpretation of structure, kinematics, and lifetime of observed cores. While our theory predicts a "characteristic" density for star formation, it also predicts that the individual critical density varies among cores; any observed sample thus contains cores at various evolutionary stages within a given density bin. By analyzing the remaining lifetime, we find cores undergoing quasi-equilibrium collapse evolve on a timescale of twice the freefall time throughout most of their life. Our analysis shows that the central column density and the associated full-width half maximum provide a reasonably accurate observational estimator of the central volume density, and therefore the freefall time; this does, however require resolving the central column density plateau. Observations with a finite beam size tend to underestimate densities of evolved cores, and this makes observed lifetimes appear to decrease more steeply than the apparent freefall time. We measure from our simulations the ratio of prestellar duration to envelope infall time, and find this is consistent with the observed relative number of prestellar cores and embedded protostars. Yet, the absolute core lifetime in our simulations is significantly shorter than would be expected from empirical measurements of the relative numbers of prestellar cores and Class II sources; we discuss several possible reasons for this discrepancy. Finally, our simulated cores have nearly constant line-of-sight velocity dispersion within the emitting region in the sky plane, resembling observed "coherent cores." We show that this "coherence" is a consequence of projection effects, which mask the intrinsic power-law velocity structure function. We discuss possible ways to estimate line-of-sight path lengths.

We compute the 3D cross-correlation between the absorption of the $z\sim 2.3$ Lyman-alpha forest measured by the COSMOS Lyman-Alpha Mapping And Tomography Observations (CLAMATO) survey, and 1642 foreground galaxies with spectroscopic redshifts from several different surveys, including 3D-HST, CLAMATO, zCOSMOS-Deep, MOSDEF, and VUDS. For each survey, we compare the measured cross-correlation with models incorporating the galaxy linear bias as well as observed redshift dispersion and systematic redshift offset. The derived redshift dispersion and offsets are generally consistent with those expected from, e.g., spectroscopic redshifts measured with UV absorption lines or NIR emission lines observed with specific instruments, but we find hints of `fingers-of-god' caused by overdensities in the field. We combine our foreground galaxy sample, and split them into 3 bins of robustly-estimated stellar mass in order to study the stellar mass-halo mass relationship. For sub-samples with median stellar masses of $\log_{10}(M_* / M_\odot) = [9.23,9.71,10.21]$, we find galaxy biases of $b_g\approx [2.9, 3.3,4.7]$, respectively. A comparison with mock measurements from the Bolshoi-Planck $N$-body simulation yields corresponding halo masses of $\log_{10}(M_* / M_\odot) \approx [10.3,11.6,12.1]$ for these stellar mass bins. At the low mass end, our results suggest enhanced star formation histories in mild tension with predictions from previous angular correlation and abundance matching-based observations, and the IllustrisTNG simulation.

Aims. The aim of this work is to determine the maximum ages that can be unambiguously established for $\delta$ Sct stars using seismic observables, and, by extension, the oldest open clusters that can be dated using this type of star. Methods. I estimate the large frequency separation using various techniques applied to two samples of $\delta$ Sct located near the red edge of the instability strip. One sample consists of 18 targets observed by the Kepler mission, and the other comprises 17 targets observed by TESS. I employ a grid of stellar models representative of typical $\delta$ Sct parameters, incorporating mass, metallicity, and rotation as independent variables, and compute the first eight radial modes for each model. Using the observed spectroscopic temperature, and the estimated large separation, I estimate the age of each star by fitting a weighted probability density function to the age distribution of the models that best match the seismic constraints. Results. To evaluate the performance of the fitting method, it was applied to a synthetic population of 20 $\delta$ Sct stars with varying metallicities and ages, generated by randomly selecting models. The analysis indicates that $\delta$ Sct stars older than 1 Gyr, but still prior to reaching the terminal-age main sequence, can in principle be reliably age-dated. Nevertheless, when the method is applied to the observational sample, only three out of the 35 stars considered marginally exceed an estimated age of 1 Gyr. Conclusions. From these results, I can say that open clusters older than approximately 1 Gyr cannot be reliably dated using astero-seismology of $\delta$ Sct stars with 1D models, at least not without a more complete treatment of convection and a non-linear treatment of rotation.

Although asteroseismology is regarded as the most powerful tool for probing stellar interiors, seismic modelling remains dependent on global stellar parameters. Stellar clusters offer direct measurements of these parameters by fitting a CMD, making the application of asteroseismology in clusters a valuable approach to advancing stellar physics modelling. We aimed to develop seismic modelling for gravity-mode pulsators in the open cluster NGC 2516 to determine stellar ages. We computed 1D stellar models using MESA, incorporating rotation-induced transport processes. Exponential overshooting was included, as well as rotationally induced mixing in the radiative envelope. Grids of evolutionary models were computed covering isochrone-derived mass ranges. The models were evolved up to 300 Myr because of the cluster's young age (~100Myr). By fitting the frequencies of identified modes of four gravity-mode member pulsators simultaneously, we measure the seismic age of the cluster NGC 2516 as 132+-8Myr. This high-precision seismic age estimate deviates by 1sigma from the isochronal age derived from public MIST isochrones for rotating stars. Our findings show that seismic modelling strongly constrains core overshooting, but because the period spacing patterns are smooth, it provides weak constraints on mixing in the radiative envelopes. The two most massive gravity-mode pulsators have MIST masses ~2.0M_sun while their seismic masses are 1.75M_sun. We constructed new asteroseismology-calibrated isochrones using input physics identical to that of our seismic model grid. While this resolves the age discrepancy, the mass discrepancy is only partially addressed. The remaining small yet persisting mass discrepancy implies a mismatch between the physics in core to surface environments of 1D stellar models and the seismic observables probing those areas of fast-rotating stars.

As sites of some of the most efficient star formation in the Universe, globular clusters (GCs) have long been hypothesized to be the building blocks of young galaxies. Within the Milky Way, our best tracers of the contribution of GCs to the proto-Galaxy are stars with such anomalous overabundance in nitrogen and depletion in oxygen ("high-[N/O] stars") that they can be identified as having originated in a cluster long after they have escaped. We identify associations between these high-[N/O] field stars and GCs using integrals of motion and metallicities and compare to chemically typical halo stars to quantify any excess association, enabling a population-level exploration of the formation sites of the nitrogen-enhanced stars in the field. Relative to the halo as a whole, high-[N/O] stars show stronger associations with the most initially massive, inner Galaxy GCs, suggesting that many nitrogen-rich stars formed in these environments. However, when compared to a sample matched in orbital energy, the excess largely disappears: high-[N/O] stars are, on average, no more associated with surviving GCs than energy-matched halo stars, despite their [N/O] abundances indicating GC origins, consistent with a scenario in which a substantial fraction of low-energy inner-halo stars originate in GCs, so an energy-matched control dilutes any differential excess. We argue that associations between high-[N/O] stars and their parent GCs are further weakened because dynamical friction and the Galactic bar have altered integrals of motion, limiting the reliability of precise present-day associations and, especially, individual star-to-cluster tagging.

To date, quantification of the on-sky motion for interstellar clouds have relied on proxies such as young stellar objects (YSO) and masers. We present the first direct measurement of an interstellar cloud proper motion using the VISTA Star Formation Atlas (VISIONS) multi-epoch infrared images of the Corona Australis star-forming region. Proper motions are extracted by tracking the morphology of extended structures in the cloud complex based on image registration techniques implemented in SimpleITK. Our determined values ($\mu_{\alpha^*} \sim +15$ mas/yr, $\mu_{\delta} \sim -30$ mas/yr) are in good agreement with those obtained for YSOs and young stellar clusters in the region. This study demonstrates the potential of image registration for directly mapping the kinematics of nearby molecular clouds, opening a new window into the study of cloud dynamics.

The diffuse interstellar band (DIB) at 6196 A exhibits notable profile variations across the Milky Way. This study addresses three open issues: the unusual broadening of the DIB profile towards Upper Sco (USco), the lack of profile variations towards stars near $\eta$ Car, and the origin of the blueshift observed in Sco OB1. Using archival spectra of 453 early-type stars across the Galactic disk and in its proximity, we created a catalogue of the DIB's profile parameters. Our analysis identified Doppler-split components within the DIB profiles across most regions with no evidence for these splits being able to account for the observed broadening (23 km/s) in USco or other regions such as Orion, Vela OB2, and Melotte 20 ($\alpha$ Per cluster). We propose that neither the ages of the studied stellar populations nor the distances between clusters and nearby clouds significantly contribute to the broadening. However, we detect a gradient in the full width at half maximum within the Sco-Cen and Orion regions, where broadening decreases with distance from the star-forming centres. This result points to a possible connection between the DIB broadening and star formation (likely via the impact of recent supernovae). Regarding the Carina Nebula, we confirm the lack of DIB profile variations in a small region near $\eta$ Car, although an adjacent southern area exhibits significant variations, comparable to those in USco. In addition to the Carina Nebula, we find that the Rosette Nebula and NGC 6405 also show consistently narrow profiles (<20 km/s) with minimal deviations from the median over spatial scales of a few parsecs. Finally, regarding the origin of the blueshift observed in Sco OB1, we used a comparison with the Lagoon Nebula and argue that the most natural explanation is the presence of an unresolved kinematic component in the profile of the DIB, shifting the measured centre of the band.

The Hydrogen-alpha (Ha) emission line in galaxies is a powerful tracer of their recent star formation activity. With the advent of JWST, we are now able to routinely observe Ha in galaxies at high redshifts (z > 3) and thus measure their star-formation rates (SFRs). However, using "classical" SFR(Ha) calibrations to derive the SFRs leads to biased results because high-redshift galaxies are commonly characterized by low metallicities and bursty star-formation histories, affecting the conversion factor between the Ha luminosity and the SFR. In this work, we develop a set of new SFR(Ha) calibrations that allow us to predict the SFRs of Ha-emitters at z > 3 with minimal error. We use the SPHINX cosmological simulations to select a sample of star-forming galaxies representative of the Ha-emitter population observed with JWST. We then derive linear corrections to the classical SFR(Ha) calibrations, taking into account variations in the physical properties (e.g., stellar metallicities) among individual galaxies. We obtain two new SFR(Ha) calibrations that, compared to the classical calibrations, reduce the root mean squared error (RMSE) in the predicted SFRs by $\Delta$RMSE $\approx$ 0.04 dex and $\Delta$RMSE $\approx$ 0.06 dex, respectively. Using the recent JWST NIRCam/grism observations of Ha-emitters at z ~ 6, we show that the new calibrations affect the high-redshift galaxy population statistics: (i) the estimated cosmic star-formation density decreases by $\Delta\rho$(SFR) $\approx$ 12%, and (ii) the observed slope of the star-formation main sequence increases by $\Delta$ $\partial$log SFR / $\partial$log M* = 0.08 $\pm$ 0.02.

Spectral line surveys of the Taurus Molecular Cloud-1 (TMC-1) have led to the detection of more than 100 new molecular species, making it the most prolific source of interstellar molecular discoveries. These wide-band, high-sensitivity line surveys have been enabled by advances in telescope and receiver technology, particularly at centimeter and millimeter wavelengths. In this work, we present a statistical analysis of the molecular inventory of TMC-1 as probed by the GOTHAM large program survey from 3.9 to 36.4 GHz. To fully unlock the potential of the $\sim$29 GHz spectral bandwidth, we developed an automated pipeline for data reduction and calibration. We applied a Bayesian approach with Markov-Chain Monte Carlo fitting to the calibrated spectra and constrained column densities for 102 molecular species detected in TMC-1, including 75 main isotopic species, 20 carbon-13 substituted species, and seven deuterium-substituted species. This list of the detected gas-phase molecules is populated by unsaturated hydrocarbons, in stark contrast to the oxygen-rich organics found in sublimated ices around protostars. Of note, ten individual aromatic molecules were identified in the GOTHAM observations, contributing 0.011% of the gas-phase carbon budget probed by detected molecules when including CO and 6% when excluding CO. This work provides a reference set of observed gas-phase molecular abundances for interstellar clouds, offering a new benchmark for astrochemical theoretical models.

Understanding the distribution and properties of molecular clouds is crucial for tracing the structure and evolution of the interstellar medium and the large-scale morphology of the Milky Way. Here we present an all-sky catalog of 3,345 molecular clouds identified from our previous three-dimensional dust reddening map using a dendrogram-based clustering method with distance-adaptive parameters. The catalog spans heliocentric distances from 90 pc to 4.3 kpc and includes key physical properties for each cloud, including position, size, mass, surface density, and dust density. Approximately 650 clouds in our catalog are associated with the boundary of the Local Bubble, while around 740 clouds (excluding those associated with the Local Bubble) are located at high Galactic latitudes ($|b| > 20^\circ$). The spatial distribution of the cataloged clouds reveals prominent large-scale features in the Galactic disk, including coherent spur-like structures, large-scale cavities, and a more detailed view of the Local Bubble shell. These findings refine our understanding of how molecular clouds trace the Galactic spiral arm network and provide new insight into the spatial structure of the Local Bubble. The catalog serves as a valuable resource for future studies of star formation, Galactic structure, and the interaction between molecular clouds and large-scale ISM features.