Astrophysics of Galaxies (astro-ph.GA)

Abstract: We report on the serendipitous discovery of an unprecedented interaction between the radio lobe of a radio galaxy and a spiral galaxy. The discovery was made thanks to LOFAR observations at 144 MHz of the galaxy cluster Abell 160 ($z=0.04317$) provided by the LOFAR Two-metre Sky Survey. The new low-frequency observations revealed that one of the radio plumes of the central galaxy GIN 049 overlaps with the spiral galaxy JO36. Previous studies carried out with MUSE revealed that the warm ionized gas in the disk of JO36, traced by the H$\alpha$ emission, is severely truncated with respect to the stellar disk. We further explore this unique system by including new uGMRT observations at 675 MHz to map the spectral index. The emerging scenario is that JO36 has interacted with the radio plume in the past 200-500 Myr. The encounter resulted in a positive feedback event for JO36 in the form of a star formation rate burst of $\sim14$ $M_\odot$ yr$^{-1}$. In turn, the galaxy passage left a trace in the radio-old plasma by re-shaping the old relativistic plasma via magnetic draping.

Abstract: Magnetic fields are fundamental to the evolution of galaxies, playing a key role in the astrophysics of the interstellar medium and star formation. Large-scale ordered magnetic fields have been mapped in the Milky Way and nearby galaxies, but it is not known how early in the Universe such structures form. Here we report the detection of linearly polarized thermal emission from dust grains in a strongly lensed, intrinsically luminous galaxy that is forming stars at a rate more than a thousand times that of the Milky Way at redshift 2.6, within 2.5 Gyr of the Big Bang. The polarized emission arises from the alignment of dust grains with the local magnetic field. The median polarization fraction is of order one per cent, similar to nearby spiral galaxies. Our observations support the presence of a 5 kiloparsec-scale ordered magnetic field with a strength of around 500uG or lower, orientated parallel to the molecular gas disk. This confirms that such structures can be rapidly formed in galaxies, early in cosmic history.

Abstract: We present a new gas-grain chemical model for the combined isotopic fractionation of carbon and nitrogen in molecular clouds, in which the isotope chemistry of carbon and nitrogen is coupled with a time-dependent description of spin-state chemistry. We updated the rate coefficients of some isotopic exchange reactions considered in the literature, and present here a set of new exchange reactions involving molecules substituted in $\rm ^{13}C$ and $\rm ^{15}N$ simultaneously. We apply the model to a series of zero-dimensional simulations representing a set of physical conditions across a prototypical prestellar core, exploring the deviations of the isotopic abundance ratios in the various molecules from the elemental isotopic ratios as a function of physical conditions and time. We find that the $\rm ^{12}C/^{13}C$ ratio can deviate from the elemental ratio by up to a factor of several depending on the molecule, and that there are highly time-dependent variations in the ratios. The $\rm HCN/H^{13}CN$ ratio, for example, can obtain values of less than 10 depending on the simulation time. The $\rm ^{14}N/^{15}N$ ratios tend to remain close to the assumed elemental ratio within $\sim$ ten per cent, with no clear trends as a function of the physical conditions. Abundance ratios between $\rm ^{13}C$-containing molecules and $\rm ^{13}C$+$\rm ^{15}N$-containing molecules show somewhat increased levels of fractionation due to the newly included exchange reactions, though still remaining within a few tens of per cent of the elemental $\rm ^{14}N/^{15}N$ ratio. Our results imply the existence of gradients in isotopic abundance ratios across prestellar cores, suggesting that detailed simulations are required to interpret observations of isotopically substituted molecules correctly, especially given that the various isotopic forms of a given molecule do not necessarily trace the same gas layers.

Abstract: We present MeerKAT HI line observations of the nearby interacting galaxy pair NGC 1512/1510. The MeerKAT data yield high-fidelity image sets characterised by an excellent combination of high angular resolution (~20") and and sensitivity (~0.08 Msun/pc^2), thereby offering the most detailed view of this well-studied system's neutral atomic hydrogen content, especially the HI co-located with the optical components of the galaxies. The stellar bulge and bar of NGC 1512 are located within a central HI depression where surface densities fall below 1 Msun/pc^2, while the galaxy's starburst ring coincides with a well-defined HI annulus delimited by a surface density of 3 Msun/pc^2. In stark contrast, the star-bursting companion, NGC 1510, has its young stellar population precisely matched to the highest HI over-densities we measure (~12.5 Msun/pc^2). The improved quality of the MeerKAT data warrants the first detailed measurements of the lengths and masses of the system's tidally-induced HI arms. We measure the longest of the two prominent HI arms to extend over ~27 kpc and to contain more than 30% of the system's total HI mass. We quantitatively explore the spatial correlation between HI and far-ultraviolet flux over a large range of HI mass surface densities spanning the outer disk. The results indicate the system's HI content to play an important role in setting the pre-conditions required for wide-spread, high-mass star formation. This work serves as a demonstration of the remarkable efficiency and accuracy with which MeerKAT can image nearby systems in HI line emission.

Abstract: Over its 13 years of operation (1990 -- 2002), the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST) observed 26 individual active galactic nuclei (AGNs) in ultraviolet (UV) imaging polarimetry. However, not all of the observations have been reduced and analyzed or set within a standardized framework. We plan to reduce and analyze the AGN observations that have been neglected in the FOC archives using a consistent, novel, and open-access reduction pipeline of our own. We then extend the method to the full AGN sample, thus leading to potential discoveries in the near future. We developed a new pipeline in Python that will be able to reduce all the FOC observations in imaging polarimetry in a homogeneous way. Most of the previously published reduced observations are dispersed throughout the literature, with the range of different analyses and approaches making it difficult to fully interpret the FOC AGN sample. By standardizing the method, we have enabled a coherent comparison among the different observational sets. In this first paper of a series exploring the full HST/FOC AGN sample, we present an exhaustively detailed account of how to properly reduce the observational data. Current progress in data-analysis is implemented in and has provided state-of-the-art UV polarimetric maps. We compare our new maps to the benchmark AGN case of NGC~1068 and successfully reproduce the main results previously published, while pushing the polarimetric exploration of this AGN futher, thanks to a finer resolution and a higher signal-to-noise ratio (S/N) than previously reported. We also present, for the first time, an optical polarimetric map of the radio-loud AGN IC~5063 and we examine the complex interactions between the AGN outflows and the surrounding interstellar medium (ISM).

Abstract: We present tests of a new method to simultaneously estimate stellar population and emission line (EL) properties of galaxies out of S-PLUS photometry. The technique uses the AlStar code, updated with an empirical prior which greatly improves its ability to estimate ELs using only the survey's 12 bands. The tests compare the output of (noise-perturbed) synthetic photometry of SDSS galaxies to properties derived from previous full spectral fitting and detailed EL analysis. For realistic signal-to-noise ratios, stellar population properties are recovered to better than 0.2 dex in masses, mean ages, metallicities and $\pm 0.2$ mag for the extinction. More importantly, ELs are recovered remarkably well for a photometric survey. We obtain input $-$ output dispersions of 0.05--0.2 dex for the equivalent widths of $[\mathrm{O}\,\rm{II}]$, $[\mathrm{O}\,\rm{III}]$, H$\beta$, H$\alpha$, $[\mathrm{N}\,\rm{II}]$, and $[\mathrm{S}\,\rm{II}]$, and even better for lines stronger than $\sim 5$ $\mathring{A}$. These excellent results are achieved by combining two empirical facts into a prior which restricts the EL space available for the fits: (1) Because, for the redshifts explored here, H$\alpha$ and $[\mathrm{N}\,\rm{II}]$ fall in a single narrow band (J0660), their combined equivalent width is always well recovered, even when $[\mathrm{N}\,\rm{II}]$/H$\alpha$ is not. (2) We know from SDSS that $W_{H\alpha+[\mathrm{N}\,\rm{II}]}$ correlates with $[\mathrm{N}\,\rm{II}]$/H$\alpha$, which can be used to tell if a galaxy belongs to the left or right wings in the classical BPT diagnostic diagram. Example applications to integrated light and spatially resolved data are also presented, including a comparison with independent results obtained with MUSE-based integral field spectroscopy.

Abstract: The Epoch of Reionization (EoR) began when galaxies grew in abundance and luminosity, so their escaping Lyman continuum (LyC) radiation started ionizing the surrounding neutral intergalactic medium (IGM). Despite significant recent progress, the nature and role of cosmic reionizers are still unclear: in order to define them, it would be necessary to directly measure their LyC escape fraction ($f_{esc}$). However, this is impossible during the EoR due to the opacity of the IGM. Consequently, many efforts at low and intermediate redshift have been made to determine measurable indirect indicators in high-redshift galaxies so that their $f_{esc}$ can be predicted. This work presents the analysis of the indirect indicators of 62 spectroscopically confirmed star-forming galaxies at $6 \leq z \leq 9$ from the Cosmic Evolution Early Release Science (CEERS) survey, combined with 12 sources with public data from other JWST-ERS campaigns. From the NIRCam and NIRSpec observations, we measured their physical and spectroscopic properties. We discovered that on average $6<z<9$ star-forming galaxies are compact in the rest-frame UV ($r_e \sim $ 0.4 kpc), are blue sources (UV-$\beta$ slope $\sim $ -2.17), and have a predicted $f_{esc}$ of about 0.13. A comparison of our results to models and predictions as well as an estimation of the ionizing budget suggests that low-mass galaxies with UV magnitudes fainter than $M_{1500} = -18$ that we currently do not characterize with JWST observations probably played a key role in the process of reionization.

Abstract: Ciii]{\lambda}{\lambda}1907, 1909 doublet emission line is a valuable tool for exploring early star-forming galaxies. It has been proposed as a potential alternative to the diminishing Ly{\alpha}{\lambda}1215.7 line for tracing galaxies during the Epoch of Reionization. In this study, we investigate the utility of the Ciii] line as a proxy for Ly{\alpha} in the reionization era by comparing the equivalent widths (EW) and velocity offsets of both emission lines. Our analysis focuses on star-forming galaxies at z \sim 3 - 4 from the VANDELS survey. We examined the spectra of 773 objects, identifying the rest-frame UV line Ciii]. Subsequently, we measured the EW of Ciii], Ly{\alpha}, and Heii. For objects displaying both Ciii] and Ly{\alpha} emission, the Ly{\alpha} velocity offsets was calculated. After removing 10 potential AGNs from our analysis, we detected Ciii] emission in 280/773 galaxies, with 139 receiving the highest confidence rating. The EW(Ciii]) had an average \sim 6 {\AA}, while EW(Ly{\alpha}) had an average \sim 18 {\AA}. Among the subset that showed both Ciii] and Ly{\alpha} (52/139), the average EW(Ciii]) was \sim 5 {\AA}, higher than those without Ly{\alpha} (EW(Ciii]) \sim 3 {\AA}). Additionally, all 52 galaxies in the Ciii] and Ly{\alpha} subset displayed a velocity shift ({\Delta}v_{Ly{\alpha}}), with average offset 533 km/s. This expanded dataset provides valuable insights, including a positive correlation between EW(Ciii]) and EW(Ly{\alpha}), confirming earlier findings. Furthermore, we report a promising anti-correlation between EW(Ciii]) and {\Delta}v_{Ly{\alpha}}, which may serve as a tool for inferring Ly{\alpha} properties and potentially detecting ionized bubbles at z \gt 6.

Abstract: We use kinematic data of proper motions from Gaia of forty-two globular and open clusters from Large Magellanic Cloud (LMC) to explore the possibility of them having extragalactic origins. We find the difference between the proper motions of cluster stars and a surrounding patch of young LMC stars in each case. We find five globular clusters towards the north-east showing a high difference (> 0.11 mas/yr, or > 25 km/s). We also examine the statistical significance of this difference taking into account both measurement errors of cluster and surrounding stars as well as inherent dispersion of stellar motions in the local galactic environment. The five globular clusters (NGC 2005, NGC 2210, NGC 1978, Hodge 3 and Hodge 11) have mean proper motions that lie outside the 85% confidence interval of the mean of surrounding young stars, with a clear outlier (NGC 1978 outside 99.96% confidence) whose difference cannot be accounted for by statistical noise. A young cluster (NGC 2100) also fitting the criteria is ruled out owing to contrary evidence from literature. This indicates a possible interaction with a dwarf galaxy resulting in the accretion/disruption in path of the five globular clusters, or possibly one or more past merger(s) of smaller galaxy/galaxies with LMC from its north-eastern region. This direction also coincides with the location of Tarantula Nebula, suggesting the possibility of the interaction event or merger having triggered its star formation activity.

Abstract: We introduce version 2.0 of the SHARK semi-analytic model of galaxy formation after many improvements to the physics included. The most significant being: (i) a model describing the exchange of angular momentum (AM) between the interstellar medium and stars; (ii) a new active galactic nuclei feedback model which has two modes, a quasar and a radio mode, with the radio mode tied to the jet energy production; (iii) a model tracking the development of black hole (BH) spins; (iv) more sophisticated modelling of environmental effects on satellite galaxies; and (v) automatic parameter exploration using Particle Swarm Optimisation. We focus on two timely research topics: the structural properties of galaxies and the quenching of massive galaxies. For the former, SHARK v2.0 is capable of producing a more realistic stellar size-mass relation with a plateau marking the transition from disk- to bulge-dominated galaxies, and scaling relations between specific AM and mass that agree well with observations. For the quenching of massive galaxies, SHARK v2.0 produces massive galaxies that are more quenched than the previous version, reproducing well the observed relations between star formation rate (SFR) and stellar mass, and specific SFR and BH mass at $z=0$. SHARK v2.0 produces a number density of massive-quiescent galaxies >1dex higher than the previous version, in good agreement with JWST observations at $z\le 5$; predicts a stellar mass function of passive galaxies in reasonably good agreement with observations at $0.5<z<5$; and environmental quenching to already be effective at $z=5$.

Abstract: Optical spectra contain a wealth of information about the physical properties and formation histories of galaxies. Often though, spectra are too noisy for this information to be accurately retrieved. In this study, we explore how machine learning methods can be used to de-noise spectra and increase the amount of information we can gain without having to turn to sample averaging methods such as spectral stacking. Using machine learning methods trained on noise-added spectra - SDSS spectra with Gaussian noise added - we investigate methods of maximising the information we can gain from these spectra, in particular from emission lines, such that more detailed analysis can be performed. We produce a variational autoencoder (VAE) model, and apply it on a sample of noise-added spectra. Compared to the flux measured in the original SDSS spectra, the model values are accurate within 0.3-0.5 dex, depending on the specific spectral line and S/N. Overall, the VAE performs better than a principle component analysis (PCA) method, in terms of reconstruction loss and accuracy of the recovered line fluxes. To demonstrate the applicability and usefulness of the method in the context of large optical spectroscopy surveys, we simulate a population of spectra with noise similar to that in galaxies at $z = 0.1$ observed by the Dark Energy Spectroscopic Instrument (DESI). We show that we can recover the shape and scatter of the MZR in this "DESI-like" sample, in a way that is not possible without the VAE-assisted de-noising.

Abstract: In this work, we investigate the discovery potential of low-mass Galactic dark matter (DM) subhaloes for indirect searches of DM. We use data from the Via Lactea II (VL-II) N-body cosmological simulation, which resolves subhaloes down to $\mathcal{O}(10^4)$ solar masses and it is thus ideal for this purpose. First, we characterize the abundance, distribution and structural properties of the VL-II subhalo population in terms of both subhalo masses and maximum circular velocities. Then, we repopulate the original simulation with millions of subhaloes of masses down to about five orders of magnitude below the minimum VL-II subhalo mass (more than one order of magnitude in velocities). We compute subhalo DM annihilation astrophysical "J-factors" and angular sizes for the entire subhalo population, by placing the Earth at a random position but at the right galactocentric distance in the simulation. Thousands of these realizations are generated in order to obtain statistically meaningful results. We find that some nearby low-mass Galactic subhaloes, not massive enough to retain stars or gas, may indeed yield DM annihilation fluxes comparable to those expected from other, more massive and acknowledgeable DM targets like dwarf satellite galaxies. Typical angular sizes are of the order of the degree, thus subhaloes potentially appearing as extended sources in gamma-ray telescopes, depending on instrument angular resolution and sensitivity. Our work shows that low-mass Galactic subhaloes with no visible counterparts are expected to play a relevant role in current and future indirect DM search searches and should indeed be considered as excellent DM targets.

Abstract: The paper presents results of studying the kinematics of the ionized gas in the galaxy of the Large Magellanic Cloud type NGC 7292 obtained with the 2.5-m telescope of the Caucasian Mountain Observatory (CMO SAI MSU) and the 6-m BTA telescope of the Special Astrophysical Observatory (SAO RAS). Analysis of the velocity fields of the ionized and neutral hydrogen showed that the kinematic center of NGC 7292 located at the center of the bar, northwest of the photometric center of the galaxy (the southeastern end of the bar) previously taken as the center of NGC 7292. In addition to the circular rotation of the gas, the radial motions associated with the bar play a significant role in the kinematics of the disk. The observed perturbations of the gaseous-disk kinematics induced by the ongoing star formation do not exceed those caused by the bar. It is possible that part of the non-circular motions (at the southeastern end of the bar which is the brightest HII region) may be related to the effects of the capture of a dwarf companion or a gaseous cloud.

Abstract: Bars are important drivers of galaxy evolution, influencing many physical processes and properties. Characterising bars is a difficult task, especially in large-scale surveys. In this work, we propose a novel morphological segmentation technique for determining bar lengths based on deep learning. We develop U-Nets capable of decomposing galaxy images into pixel masks highlighting the regions corresponding to bars and spiral arms. We demonstrate the versatility of this technique through applying our models to galaxy images from two different observational datasets with different source imagery, and to RGB colour and monochromatic galaxy imaging. We apply our models to analyse SDSS and Subaru HSC imaging of barred galaxies from the NA10 and SAMI catalogues in order to determine the dependence of bar length on stellar mass, morphology, redshift and the spin parameter proxy $\lambda_{R_e}$. Based on the predicted bar masks, we show that the relative bar scale length varies with morphology, with early type galaxies hosting longer bars. While bars are longer in more massive galaxies in absolute terms, relative to the galaxy disc they are actually shorter. We also find that the normalised bar length decreases with increasing redshift, with bars in early-type galaxies exhibiting the strongest rate of decline. We show that it is possible to distinguish spiral arms and bars in monochrome imaging, although for a given galaxy the estimated length in monochrome tends to be longer than in colour imaging. Our morphological segmentation technique can be efficiently applied to study bars in large-scale surveys and even in cosmological simulations.

Abstract: A significant part of barred disc galaxies exhibits boxy/peanut-shaped structures (B/PS bulges) at high inclinations. Another structure also associated with the bar is a barlens, often observed in galaxies in a position close to face-on. At this viewing angle, special kinematic tests are required to detect a 3D extension of the bars in the vertical direction (B/PS bulges). We use four pure $N$-body models of galaxies with B/PS bulges, which have different bar morphology from bars with barlenses to the so-called face-on peanut bars. We analyse the kinematics of our models to establish how the structural features of B/PS bulges manifest themselves in the kinematics for galaxies at intermediate inclinations and whether these features are related to the barlenses. We apply the dissection of the bar into different orbital groups to determine which of them are responsible for the features of the LOSVD (line-of-sight velocity distribution), i.e., for the deep minima of the $h_4$ parameter along the major axis of the bar. As a result, we claim that for our models at the face-on position, the kinematic signatures of a `peanut' indeed track the vertical density distribution features. We conclude that orbits responsible for such kinematic signatures differ from model to model. We pay special attention to the barlens model. We show that orbits assembled into barlens are not responsible for the kinematic signatures of B/PS bulges. The results presented in this work are applicable to the interpretation of IFU observations of real galaxies.

Abstract: The generation and evolution of dust in galaxies are important tracers for star formation, and can characterize the rest-frame ultraviolet to infrared emission from the galaxies. In particular understanding dust in high-redshift galaxies are important for observational cosmology, as they would be necessary to extract information on star formation in the early universe. We update the public semi-analytical model A-SLOTH (Ancient Stars and Local Observables by Tracing Halos) to model the evolution of dust, focusing on high-redshift star-forming galaxies with stellar masses of $\sim 10^8$--$10^{10}M_\odot$ observed by ALMA ($z\approx 7$) and JWST ($z\approx 11$). We find that these galaxies should qualitatively differ in their star formation properties; while the samples in ALMA are explained by dust growth in normal star-forming galaxies, the lack of dust in the samples by JWST requires dust ejection by radiation pressure due to recent highly efficient star-formation within a few 10 Myr, with order 100 times higher efficiency than normal galaxies calibrated by A-SLOTH. Depending on where the JWST galaxies locate on the luminosity function, their bursty star formation histories inferred from our model can have impacts for rates of star formation, supernova explosion, stellar feedback, and detectability of dusty, mature galaxies in the very early universe.