Accurate estimation of dark matter halo masses for galaxy groups is central to studies of galaxy evolution and for leveraging group catalogues as cosmological probes. In this work, we present a comprehensive evaluation and calibration of two complementary halo mass estimators: a dynamical estimator based on a modified virial theorem (MVT) and an empirical summed stellar mass to halo mass relation (sSHMR), which uses the summed mass of the three most massive group galaxies as a proxy for halo mass. Using a suite of state-of-the-art semi-analytic models (SAMs; Shark, SAGE, and GAEA) to produce observationally motivated mock light-cone catalogues, we rigorously quantify the accuracy, uncertainty, and model dependence of each method. The MVT halo mass estimator achieves negligible systematic bias (mean Delta = -0.01 dex) and low scatter (mean sigma = 0.20 dex) as a function of the predicted halo mass, with no sensitivity to the SAM baryonic physics. The calibrated sSHMR yields the highest precision, with mean Delta = 0.02 dex and mean sigma= 0.14 dex as a function of the predicted halo mass but exhibits greater model dependence due to its sensitivity to varying baryonic physics and physical prescriptions across the SAMs. We demonstrate the application of these estimators to observational group catalogues, including the construction of the empirical halo mass function and the mapping of quenched fractions in the stellar mass-halo mass plane. We provide clear guidance on the optimal application of each method: the MVT is recommended for GAMA-like surveys (i < 19.2) calibrated to z < 0.1 and should be used for studies that require minimal model dependence, while the sSHMR is optimal for high-precision halo mass estimation across diverse catalogues with magnitude limits of Z < 21.2 or brighter and to redshifts of z <= 0.3. These calibrated estimators will be of particular value for upcoming wide-area spectroscopic surveys, enabling robust and precise analyses between the galaxy-halo connection and the underlying dark matter distribution.

In this work, we present source-tailored Wide-field Infrared Survey Explorer (WISE) mid-infrared photometry (at 3.4, 4.6, 12, and 23 μ m) of 2812 galaxies in the extended Spitzer Survey of Stellar Structure in Galaxies sample, and characterize the mid-infrared colors and dust properties of this legacy nearby galaxy data set. Informed by the relative emission between W3 (12 μ m) and W4 (23 μ m), we rederive star formation rate (SFR) scaling relations calibrated to L TIR , which results in improved agreement between the two tracers. By inverse–variance weighting the W3 and W4-derived SFRs, we generate a combined mid-infrared SFR that is a broadly robust measure of star formation activity in dusty, star-forming galaxies in the nearby Universe. In addition, we investigate the use of a W3-derived dust density metric, Σ 12 μ m ( L ⊙ /kpc 2 ), to estimate the SFR deficit of low mass, low dust galaxies. This is achieved by combining WISE with existing Galaxy Evolution Explorer ultraviolet (UV) photometry, which we further use to explore the relationship between dust and UV emission as a function of morphology. Finally, we use our derived SFR prescriptions to examine the location of galaxies in the log SFR–log M stellar plane, as a function of morphological type, which underscores the complexity of dust-derived properties seen in galaxies of progressively earlier type.

The broad-band radio spectral energy distribution (SED) of star-forming galaxies (SFGs) contains a wealth of complex physics. We aim to determine the physical emission and loss processes causing radio SED curvature and steepening to see which observed global astrophysical properties are correlated with radio SED complexity. We have acquired radio continuum data between 70 MHz and 17 GHz for a sample of 19 southern local (z < 0.04) SFGs. Of this sample 11 are selected to contain low-frequency (< 300 MHz) turnovers (LFTOs) in their SEDs and eight are control galaxies with similar global properties. We model the radio SEDs for our sample using a Bayesian framework whereby radio emission (synchrotron and free-free) and absorption or loss processes are included modularly. We find that without the inclusion of higher frequency data, single synchrotron power-law based models are always preferred for our sample; however, additional processes including free-free absorption (FFA) and synchrotron losses are often required to accurately model radio SED complexity in SFGs. The fitted synchrotron spectral indices range from -0.45 to -1.07 and are strongly anticorrelated with stellar mass suggesting that synchrotron losses are the dominant mechanism acting to steepen the spectral index in larger nearby SFGs. We find that LFTOs in the radio SED are independent from the inclination. The merging systems in our SFG sample have elevated specific star formation rates and flatter fitted spectral indices with unconstrained LFTOs. Lastly, we find no significant separation in global properties between SFGs with or without modelled LFTOs. Overall LFTOs are likely caused by a combination of FFA and ionisation losses in individual recent starburst regions with specific orientations and interstellar medium properties that, when averaged over the entire galaxy, do not correlate with global astrophysical properties.

We examine the optical counterparts of the 1829 neutral hydrogen (HI) detections in three pilot fields in the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) using data from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys DR10. We find that 17 per cent (315) of the detections are optically low surface brightness galaxies (LSBGs; mean g-band surface brightness within 1 R_e of > 23 mag arcsec^-2) and 3 per cent (55) are optically 'dark'. We find that the gas-rich WALLABY LSBGs have low star formation efficiencies, and have stellar masses spanning five orders of magnitude, which highlights the diversity of properties across our sample. 75 per cent of the LSBGs and all of the dark HI sources had not been catalogued prior to WALLABY. We examine the optically dark sample of the WALLABY pilot survey to verify the fidelity of the catalogue and investigate the implications for the full survey for identifying dark HI sources. We assess the HI detections without optical counterparts and identify 38 which pass further reliability tests. Of these, we find that 13 show signatures of tidal interactions. The remaining 25 detections have no obvious tidal origin, so are candidates for isolated galaxies with high HI masses, but low stellar masses and star-formation rates. Deeper HI and optical follow-up observations are required to verify the true nature of these dark sources.

Current and future surveys rely on machine learning classification to obtain large and complete samples of transients. Many of these algorithms are restricted by training samples that contain a limited number of spectroscopically confirmed events. Here, we present the first real-time application of Active Learning to optimise spectroscopic follow-up with the goal of improving training sets of early type Ia supernovae (SNe Ia) classifiers. Using a photometric classifier for early SN Ia, we apply an Active Learning strategy for follow-up optimisation using the real-time FINK broker processing of the ZTF public stream. We perform follow-up observations at the ANU 2.3m telescope in Australia and obtain 92 spectroscopic classified events that are incorporated in our training set. We show that our follow-up strategy yields a training set that, with 25% less spectra, improves classification metrics when compared to publicly reported spectra. Our strategy selects in average fainter events and, not only supernovae types, but also microlensing events and flaring stars which are usually not incorporated on training sets. Our results confirm the effectiveness of active learning strategies to construct optimal training samples for astronomical classifiers. With the Rubin Observatory LSST soon online, we propose improvements to obtain earlier candidates and optimise follow-up. This work paves the way to the deployment of real-time AL follow-up strategies in the era of large surveys.

We present a new catalog of 196 galaxies of the nearby Hydra I cluster out to ∼1.75r_200, consisting of broad u,g,r,i,z along with narrowband Hα measurements. These deep optical images were obtained with the DECam camera (CTIO) and reach down to a surface brightness limit of μ( 3σ;10”×10”)=26.9 mag arcsec^2 in the g band. We also report the HI properties for 89 cluster members detected with MeerKAT. A color magnitude diagram (CMD) shows a bimodal distribution typical of a cluster population, more evolved than those found in isolation. We combine optical Hα and WISE infrared data to compare the star formation history at two distinct timescales. Differences in the star forming activity depicted by both populations manifest as starburst in 24 found members. Of these, 18 starburst galaxies have neutral gas measurements, and show disturbed HI disks that suggest an environmentally-triggered boost in star formation within the last 10^7 yrs. Processes such as ram pressure stripping or tidal interactions may underlie their enhanced star-forming activity and asymmetric disks. Since Hydra's dynamical history is unclear, we examine the spatial and velocity distribution of the sample. We reveal a possible link between the large scale structure feeding the Hydra I cluster and the heightened star-forming activity of the starburst galaxies. This feeding pattern matches the few substructure that has been identified in Hydra in previous works, and may explain its origin. Our results portray a picture of a cluster with an evolved nature, plus a population of new infalling galaxies that manifest the impact of their first contact with the cluster environment through star formation, color, morphology and gas content transformations.

We have examined the nuclear spectra of very massive star-forming galaxies at z similar to 0 to understand how they differ from other galaxies with comparable masses, which are typically passive. We selected a sample of 126 nearby massive star-forming galaxies (< 100 Mpc, 1011.3 M circle dot <= Mstellar <= 1011.7 M circle dot,1M circle dot yr-1 < SFR < 13 M circle dot yr-1) from the 2MRS-Bright WXSC catalogue. LEDA morphologies indicate at least 63% of our galaxies are spirals, while visual inspection of Dark Energy Survey images reveals 75% of our galaxies to be spirals with the remainder being lenticular. Of our sample 59 have archival nuclear spectra, which we have modelled and subsequently measured emission lines ([NII]lambda 6583, H alpha lambda 6563, [OIII]lambda 5008, and H beta lambda 4863), classifying galaxies as star-forming, LINERs or AGNs. Using a BPT diagram we find 83 +/- 6% of our galaxies, with sufficient signal-to-noise to measure all 4 emission lines, to be LINERs. Using the [NII]lambda 6583/H alpha lambda 6563 emission line ratio alone we find that 79 +/- 6% of the galaxies (46 galaxies) with archival spectra are LINERs, whereas just similar to 30% of the overall massive galaxy population are LINERs (Belfiore et al. 2016, MNRAS, 461, 3111). Our sample can be considered a local analogue of the Ogle et al. (2019, VizieR Online Data Catalog, p. J/ApJS/243/14; 2016, ApJ, 817, 109) sample of z similar to 0.22 massive star-forming galaxies in terms of selection criteria, and we find 64% of their galaxies are LINERs using SDSS spectra. The high frequency of LINER emission in these massive star-forming galaxies indicates that LINER emission in massive galaxies may be linked to the presence of gas that fuels star formatio

Environment has long been known to have an impact on the evolution of galaxies, but disentangling its impact from mass evolution requires the careful analysis of statistically significant samples. By implementing cutting-edge visualisation methods to test and validate group-finding algorithms, we utilise a mass-complete sample of galaxies to z < 0.1 comprised of spectroscopic redshifts from prominent surveys such as the 2-degree Field Galaxy Redshift Survey and the Galaxy and Mass Assembly Survey. Utilising our group finding methods, we find 1 413 galaxy groups made up of 8 990 galaxies corresponding to 36% of galaxies associated with group environments. We also search for close pairs, with separations of r sep < 50 h(-1)kpc and v sep < 500 km s-1 within our sample and further classified them into major ( M (sec) / M- prim <= 0.25) and minor ( M (sec) / M (prim) > 0.25) pairs. To examine the impact of environmental factors, we employ bespoke WISE photometry, which facilitates accurate measurements of stellar mass and star formation rates and hence the best possible description of the variation of galaxy properties as a function of the local environment. Our analysis, employing a derived star-forming main sequence relation, reveals that star-formation (SF) within galaxies are pre-processed as a function of group membership. This is evident from the evolution of the star-forming and quenched population of galaxies. We see an increase in the fraction of quiescent galaxies relative to the field as group membership increases, and this excess of quenched galaxies relative to the field is later quantified through the use of the environmental quenching efficiency ( epsilon env ) metric. Within the star-forming population, we observe SF pre-processing with the relative difference in specific star formation rates (OsSFR), where we see a net decrease in SF as group membership increases, particularly at larger stellar masses. We again quantify this change within the SF population with our star formation deficiency ( epsilon SFD ) metric. Our sample of close pairs at low stellar masses exhibit enhanced star formation efficiencies compared to the field, and at larger stellar mass ranges show large deficiencies. Separating the close pairs into major/minors and primary/secondaries reveals SF enhancements projected separation decreases within the minor pairs, this effect is even more pronounced within minor primaries. This research emphasises the importance of carefully studying the properties of galaxies within group environments to better understand the pre-processing of SF within galaxies. Our results show that the small-scale environments of galaxies influence star- forming properties even when stellar masses are kept constant. This demonstrates that galaxies do not evolve in isolation over cosmic time but are shaped by a complex interaction between their internal dynamics and external influences.

Large sky surveys from dedicated survey telescopes allow astronomers to access large swathes of the optical and near-infrared sky at high spatial resolution. The increasingly large volume of multi-wavelength imaging and catalogue photometry data products they generate are a cumbersome data management burden for survey teams. Even the simplest of tasks like visual inspection can quickly become out of reach when trying to apply the traditional astronomical software toolkit familiar to most astronomers. More complex tasks like quality assurance and scientific exploitation demand interactive visualisation of data products alone (e.g. catalogues overlaid on imaging) and in conjunction with multi-wavelength data from other surveys. Here we introduce a web application that effortlessly performs these tasks for the reprocessed imaging (>20TB) and catalogues (>100GB) of the VISTA Hemisphere Survey. The application is powered by the asynchronous architecture developed for Data Central's Data Aggregation Service that can query and receive several data streams simultaneously. Users can inspect a single target or navigate multiple targets from an uploaded list. Survey images are dynamically converted from FITS to HiPS format before being loaded into an Aladin Lite instance. Multiple catalogues are retrieved and accurately drawn in Aladin Lite using markers and ellipses. Dynamically generated tables summarise catalogue metadata with links to full record information. Users requiring more than the provided visualisation and adjustable image scaling can download image and catalogue cutouts for closer inspection. With further science-oriented refinement we plan to release the application as part of the Data Central science platform.

ABSTRACT It has been suggested that the bulge-to-total stellar mass ratio or feedback from black holes (BHs), traced by the BH-to-(total stellar) mass ratio, might establish a galaxy’s specific star formation rate (sSFR). We reveal that a galaxy’s morphology – reflecting its formation history, particularly accretions and mergers – is a far better determinant of the sSFR. Consequently, we suggest that galaxy formation models which regulate the sSFR primarily through BH feedback prescriptions or bulge-regulated disc fragmentation consider acquisitions and mergers which establish the galaxy morphology. We additionally make several new observations regarding current (z ∼ 0) star-formation rates. (i) Galaxies with little to no star formation have bulges with an extensive range of stellar masses; bulge mass does not dictate presence/absence on the ‘star-forming main sequence’. (ii) The (wet merger)-built, dust-rich S0 galaxies are the ‘green valley’ bridging population between elliptical galaxies on the ‘red sequence’ and spiral galaxies on the blue star-forming main sequence. (iii) The dust-poor S0 galaxies are not on the star-forming main sequence nor in the ‘green valley’. Instead, they wait in the field for gas accretion and/or minor mergers to transform them into spiral galaxies. Mid-infrared sample selection can miss these (primordial) low dust-content and low stellar-luminosity S0 galaxies. Finally, the appearance of the quasi-triangular-shaped galaxy-assembly sequence, previously dubbed the `Triangal', which tracks the morphological evolution of galaxies, is revealed in the sSFR-(stellar mass) diagram.

Empirical correlations connecting starlight to galaxy dynamics (e.g., the fundamental plane (FP) of elliptical/quiescent (Q) galaxies and the Tully–Fisher relation of spiral/star-forming (SF) galaxies) provide cosmology-independent distance estimation and are central to local Universe cosmology. In this work, we introduce the mass hyperplane (MH), which is the stellar-to-dynamical mass relation ( M ⋆ / M dyn ) recast as a linear distance indicator. Building on recent FP studies, we show that both SF and Q galaxies follow the same empirical MH, then use this to measure the peculiar velocities (PVs) for a sample of 2496 galaxies at z < 0.12 from GAMA. The limiting precision of MH-derived distance/PV estimates is set by the intrinsic scatter in size, which we find to be ≈0.1 dex for both Q and SF galaxies (when modeled independently) and ≈0.11 dex when all galaxies are modeled together, showing that the MH is as good as the FP. To empirically validate our framework and distance/PV estimates, we compare the inferred distances to groups as derived using either Q or SF galaxies. A good agreement is obtained with no discernible bias or offset, having a scatter of ≈0.05 dex ≈12% in distance. Further, we compare our PV measurements for the Q galaxies to the previous PV measurements of the galaxies in common between GAMA and the Sloan Digital Sky Survey, which shows similarly good agreement. Finally, we provide comparisons of PV measurements made with the FP and the MH, then discuss possible improvements in the context of upcoming surveys such as the 4MOST Hemisphere Survey.

We demonstrate the importance of radio selection in probing heavily obscured galaxy populations. We combine Evolutionary Map of the Universe (EMU) Early Science data in the Galaxy and Mass Assembly (GAMA) G23 field with the GAMA data, providing optical photometry and spectral line measurements, together with Wide-field Infrared Survey Explorer (WISE) infrared (IR) photometry, providing IR luminosities and colours. We investigate the degree of obscuration in star forming galaxies, based on the Balmer decrement (BD), and explore how this trend varies, over a redshift range of 0<z<0.345. We demonstrate that the radio detected population has on average higher levels of obscuration than the parent optical sample, arising through missing the lowest BD and lowest mass galaxies, which are also the lower star formation rate (SFR) and metallicity systems. We discuss possible explanations for this result, including speculation around whether it might arise from steeper stellar initial mass functions in low mass, low SFR galaxies.

Aims. We investigate how di ff erent mid-infrared (mid-IR) properties of galaxies are correlated with the environment in which the galaxies are located. For this purpose, we first study the dependence of galaxy clustering on the absolute magnitude at 3.4 µ m and redshift. Then, we look into the environmental dependence of mid-IR luminosities and the galaxy properties derived from these luminosities. We also explore how various IR galaxy luminosity selections influence the galaxy clustering measurements. Methods. We used a set of W1 (3.4 µ m) absolute magnitude ( M W1 ) selected samples from the Galaxy and Mass Assembly (GAMA) survey matched with mid-IR properties from the Wide-field Infrared Survey Explorer (WISE) in the redshift range 0 . 07 ≤ z < 0 . 43. We computed the galaxy two-point correlation function (2pCF) and compared the clustering lengths between subsamples binned in M W1 and in redshift. We also measured the marked correlation function (MCF), in which the galaxies are weighted by marks when measuring clustering statistics, using the luminosities in the WISE W1 to W4 (3.4 to 22 µ m) bands as marks. Additionally, we compared the measurements of MCFs with di ff erent estimates of stellar mass and star formation rate (SFR) used as marks. Finally, we checked how di ff erent selections applied to the sample a ff ect the clustering measurements. Results. We show strong clustering dependence on the W1 absolute magnitude: galaxies brighter in the W1 band are more strongly clustered than their fainter counterparts. We also observe a lack of significant redshift dependence of clustering in the redshift range 0 . 07 ≤ z < 0 . 43. We show that although the W1 and W2 bands are direct indicators of stellar mass, a galaxy sample selected based on W1 or W2 bands does not perfectly show the clustering behaviour of a stellar mass-selected sample. The proxy relation between W3 and W4 bands and SFR is similar. We also demonstrate the influence of estimation techniques of stellar mass and SFR on the clustering measurements.

ABSTRACT Using mid-infrared star formation rate and stellar mass indicators in WISE (Wide-field Infrared Survey Explorer), we construct and contrast the relation between star formation rate and stellar mass for isolated and paired galaxies. Our samples comprise a selection of AMIGA (Analysis of the interstellar Medium in Isolated GAlaxies; isolated galaxies) and pairs of ALFALFA (Arecibo Legacy Fast ALFA) galaxies with H i detections such that we can examine the relationship between H i content (gas fraction, H i deficiency) and galaxy location on the main sequence (MS) in these two contrasting environments. We derive for the first time an H i scaling relation for isolated galaxies using WISE stellar masses, and thereby establish a baseline predictor of H i content that can be used to assess the impact of environment on H i content when compared with samples of galaxies in different environments. We use this updated relation to determine the H i deficiency of both our paired and isolated galaxies. Across all the quantities examined as a function of environment in this work (MS location, gas fraction, and H i deficiency), the AMIGA sample of isolated galaxies is found to have the lower dispersion: σAMIGA = 0.37 versus σPAIRS = 0.55 on the MS, σAMIGA = 0.44 versus σPAIRS = 0.54 in gas fraction, and σAMIGA = 0.28 versus σPAIRS = 0.34 in H i deficiency. We also note fewer isolated quiescent galaxies, 3 (0.6${{\ \rm per\ cent}}$), compared to 12 (2.3${{\ \rm per\ cent}}$) quiescent pair members. Our results suggest the differences in scatter measured between our samples are environment driven. Galaxies in isolation behave relatively predictably, and galaxies in more densely populated environments adopt a more stochastic behaviour, across a broad range of quantities.

We combine James Webb Space Telescope (JWST) and Hubble Space Telescope imaging with Atacama Large Millimeter Array CO(2–1) spectroscopy to study the highly turbulent multiphase intergalactic medium (IGM) in Stephan’s Quintet on 25–150 pc scales. Previous Spitzer observations revealed luminous H 2 line cooling across a 45 kpc-long filament, created by a giant shock wave, following the collision with an intruder galaxy, NGC 7318b. We demonstrate that the Mid-Infrared Instrument/F1000W/F770W filters are dominated by 0–0 S(3) H 2 and a combination of polycyclic aromatic hydrocarbon and 0–0 S(5) H 2 emission. These observations reveal the dissipation of kinetic energy as massive clouds experience collisions, interactions, and likely destruction/recycling within different phases of the IGM. In 1 kpc-scaled structure, warm H 2 was seen to form a triangular-shaped head and tail of compressed and stripped gas behind a narrow shell of cold H 2 . In another region, two cold molecular clumps with very different velocities are connected by an arrow-shaped stream of warm, probably shocked, H 2 suggesting a cloud–cloud collision is occurring. In both regions, a high warm-to-cold molecular gas fraction indicates that the cold clouds are being disrupted and converted into warm gas. We also map gas associated with an apparently forming dwarf galaxy. We suggest that the primary mechanism for exciting strong mid-IR H 2 lines throughout Stephan’s Quintet is through a fog of warm gas created by the shattering of denser cold molecular clouds and mixing/recycling in the post-shocked gas. A full picture of the diverse kinematics and excitation of the warm H 2 will require future JWST mid-IR spectroscopy. The current observations reveal the rich variety of ways that different gas phases can interact with one another.

We combine JWST and HST imaging with ALMA~CO(2-1) spectroscopy to study the highly turbulent multi-phase intergalactic medium (IGM) in Stephan's Quintet on 25-150 pc scales. Previous Spitzer observations revealed luminous H$_2$ line cooling across a 45 kpc-long filament, created by a giant shock-wave, following the collision with an intruder galaxy NGC~7318b. We demonstrate that the MIRI/F1000W/F770W filters are dominated by 0-0~S(3)~H$_2$ and a combination of PAH and 0-0~S(5)~H$_2$ emission. They reveal the dissipation of kinetic energy as massive clouds experience collisions, interactions and likely destruction/re-cycling within different phases of the IGM. In one kpc-scaled structure, warm H$_2$ formed a triangular-shaped head and tail of compressed and stripped gas behind a narrow shell of cold H$_2$. In another region, two cold molecular clumps with very different velocities are connected by an arrow-shaped stream of warm, probably shocked, H$_2$ suggesting a cloud-cloud collision is occurring. In both regions, a high warm-to-cold molecular gas fraction indicates that the cold clouds are being disrupted and converted into warm gas. We also map gas associated with an apparently forming dwarf galaxy. We suggest that the primary mechanism for exciting strong mid-IR H$_2$ lines throughout Stephan's Quintet is through a fog of warm gas created by the shattering of denser cold molecular clouds and mixing/recycling in the post-shocked gas. A full picture of the diverse kinematics and excitation of the warm H$_2$ will require future JWST mid-IR spectroscopy. The current observations reveal the rich variety of ways that different gas phases can interact with one another.

ABSTRACT We develop a framework for using clustering-based redshift inference (cluster-$z$ ) to measure the evolving galaxy luminosity function (GLF) and galaxy stellar mass function (GSMF) using Wide-field Infrared Survey Explorer W1 (3.4 μm) mid-infrared photometry and positions. We use multiple reference sets from the Galaxy And Mass Assembly survey, Sloan Digital Sky Survey and Baryon Oscillation Spectroscopic Survey. Combining the resulting cluster-$z$ s allows us to enlarge the study area, and by accounting for the specific properties of each reference set, making best use of each reference set to produce the best overall result. Thus we are able to measure the GLF and GSMF over ∼7500 deg2 of the Northern Galactic Cap up to $z$ < 0.6. Our method can easily be adapted for new studies with fainter magnitudes, which pose difficulties for the derivation of photo-$z$ s. With better statistics in future surveys this technique is a strong candidate for studies with new emerging data from, e.g. the Vera C Rubin Observatory, the Euclid mission or the Nancy Grace Roman Space Telescope.

We derive new empirical scaling relations between WISE mid-infrared galaxy photometry and well-determined stellar masses from SED modeling of a suite of optical-infrared photometry provided by the DR4 Catalogue of the GAMA-KiDS-VIKING survey of the southern G23 field. The mid-infrared source extraction and characterization are drawn from the WISE Extended Source Catalogue (WXSC) and the archival ALLWISE catalog, combining both resolved and compact galaxies in the G23 sample to a redshift of 0.15. Three scaling relations are derived: W1 3.4 micron luminosity versus stellar mass, and WISE W1-W2, W1-W3 colors versus mass-to-light ratio (sensitive to a variety of galaxy types from passive to star-forming). For each galaxy in the sample, we then derive the combined stellar mass from these scaling relations, producing Mstellar estimates with better than ∼25-30 >10^9 Msolar and <40 - 50 provide simple prescriptions for rest-frame corrections and estimating stellar masses using only the W1 flux and the W1-W2 color, making stellar masses more accessible to users of the WISE data. Given a redshift or distance, these new scaling relations will enable stellar mass estimates for any galaxy in the sky detected by WISE with high fidelity across a range of mass-to-light.

AbstractWe present a new high-resolution neutral atomic hydrogen (Hi) survey of ring galaxies using the Australia Telescope Compact Array (ATCA). We target a sample of 24 ring galaxies from the Buta (1995) Southern Ring Galaxy Survey Catalogue in order to study the origin of resonance-, collisional- and interaction-driven ring galaxies. In this work, we present an overview of the sample and study their global and resolved Hiproperties. In addition, we also probe their star formation properties by measuring their star formation rates (SFR) and their resolved SFR surface density profiles. We find that a majority of the barred galaxies in our sample are Hi-deficient, alluding to the effects of the bar in driving their Hideficiency. Furthermore, for the secularly evolving barred ring galaxies in our sample, we apply Lindblad’s resonance theory to predict the location of the resonance rings and find very good agreement between predictions and observations. We identify rings of Higas and/or star formation co-located at one or the other major resonances. Lastly, we measure the bar pattern speed ($\Omega_{\textrm{bar}}$) for a sub-sample of our galaxies and find that the values range from 10–90$\textrm{km s}^{-1}$kpc$^{-1}$, in good agreement with previous studies.

Hickson Compact Groups (HCGs) are dense configurations of 4 to 10 galaxies, whose HI (neutral gas) morphology appears to follow an evolutionary sequence of three phases, with gas initially confined to galaxies, then significant amounts spread throughout the intra-group medium, and finally with almost no gas remaining in the galaxies themselves. The HI deficiency of HCGs is expected to increase as the HI morphological phase progresses along this sequence, potentially making it a useful proxy for evolutionary phase. We test this hypothesis for the first time with a large sample of 38 HCGs with VLA HI observations that are uniformly reduced and analysed with a purpose-built pipeline. However, we find little evidence that HI deficiency can be used as a proxy for the evolutionary phase of a HCG in either of the first two phases, with the distribution of HI deficiency being consistent in both, although it does greatly increase in the third phase. This appears to be the result to three factors: a) there is already a broad range of HI deficiencies in Phase 1 HCGs, possibly due to their differing locations relative to large scale structures; b) the timescale for major interactions and morphological changes is, in general, considerably shorter than the timescale for the destruction or consumption of HI gas; and c) some groups have their HI content rejuvenated by the late addition of a new gas-rich member (for which we added a new sub-phase, 3c, to the established evolutionary sequence). Finally, across all HCGs studied, we identify only a few cases where there is strong evidence for the existence of a previously proposed diffuse HI component in the intra-group medium, which might be detectable with improved observations. This work was completed with considerable attention paid to scientific reproducibility, and all reduction and analysis has been made public via Github and Zenodo. (Abridged)