Cosmic filaments have been recognised as influencing galaxy evolution, but their connection to galactic cold gas reservoirs is elusive, particularly at low redshifts. We investigate the influence of filaments on neutral hydrogen (HI) detections in galaxies at 0.02<z<0.09, using the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) survey in the COSMOS and XMM-LSS fields. We measure the fraction of optical galaxies from the Dark Energy Spectroscopic Instrument (DESI) Survey detected in HI emission as a function of stellar mass, morphology, local density, and the distance to the nearest filament. We find that galaxies closer to filaments have higher stellar masses, higher local densities, and a larger early-type fraction, all of which affect the HI detection. After controlling for these dependencies, filaments have measurable effects on HI detection. Late-type galaxies in low-local density environments show reduced HI detection fractions close to filaments across all stellar mass ranges, suggesting potential gas depletion through ram pressure stripping and cosmic web detachment. Massive early-type galaxies show an enhanced HI detection fraction in filaments compared to the voids, suggesting possible gas replenishment through filamentary accretion or gas-rich mergers. Our results suggest that cosmic filaments influence galactic HI gas reservoirs through various competing processes, whose relative importance varies with stellar mass and local density.

We present new Hubble Space Telescope (HST) imaging of three recently discovered star-forming dwarf galaxies beyond the Local Group: Pavo, Corvus A, and Kamino. The discovery of Kamino is reported here for the first time. They rank among the most isolated faint dwarf galaxies known; hence they provide unique opportunities to study galaxy evolution at the smallest scales, free from the environmental effects of more massive galaxies. Our HST data reach similar to 2-4 magnitudes below the tip of the red giant branch (TRGB) for each dwarf, allowing us to measure their distances, structural properties, and recent star formation histories (SFHs). All three galaxies contain a complex stellar population of young and old stars, and are typical of field galaxies in this mass regime (MV = -10.62 +/- 0.08 and D=2.16-0.07+0.08 Mpc for Pavo, MV = -10.91 +/- 0.10 and D = 3.34 +/- 0.11 Mpc for Corvus A, and MV = -12.02 +/- 0.12 and D=6.50-0.11+0.15 Mpc for Kamino). Our HST-derived SFHs reveal differences among the three dwarfs: Pavo and Kamino show relatively steady, continuous star formation, while Corvus A formed similar to 60% of its stellar mass by 10 Gyr ago. These results align with theoretical predictions of diverse evolutionary pathways for isolated low-mass galaxies.

We present Hubble Space Telescope (HST) imaging of Pegasus V and Pisces VII, along with a re-analysis of the archival imaging of Pegasus W, and Karl Jansky Very Large Array (VLA) neutral gas (H i ) observations of all three. These three ultra-faint dwarfs (UFDs) are all within the Local Group in the approximate direction of M31. The VLA observations place stringent upper limits on their H i content, with all having M _HI < 10 ^4 M _⊙ . As the red giant branches of these UFDs are sparsely populated, we determined distances from the HST photometry of horizontal branch (HB) stars in comparison to a fiducial HB population (from M92), with all three falling in the range 0.7–1 Mpc. Using a new Python -based star formation history (SFH) fitting code (based on StarFISH ), we derive SFHs of all three UFDs. As found previously, the best-fit SFH for Pegasus W includes significant star formation well beyond the end of reionization, while the SFHs calculated for Pegasus V and Pisces VII are consistent with them having quenched over 10 Gyr ago. These findings for the latter two objects indicate that, like those in the vicinity of the Milky Way, lower-mass UFDs in the vicinity of M31 likely quenched at early times.

The recent gravitational-wave (GW) alert from a compact object merger involving at least one subsolar mass (SSM) object has prompted questions about their origins. S251112cm is reported by LIGO/Virgo with a false alarm rate of 1 per 6.2 years, nearby luminosity distance 93 ± 27 Mpc, probability of containing a SSM object of 100

We present early science results from the Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE) program, which targets 40 Virgo Cluster galaxies to investigate the effect of environment on the interstellar medium (ISM) at similar to 100 pc scales. From 12 galaxies in the MAUVE-Multi Unit Spectroscopic Explorer (MUSE) early sample, we find systematically elevated line ratios compared to Physics at High Angular resolution in Nearby GalaxieS (PHANGS)-MUSE field disks, with higher medians of [N ii]/H alpha (0.75 versus 0.50), [S ii]/H alpha (0.57 versus 0.49), and [O iii]/H beta (1.04 versus 0.68). Spatially resolved Baldwin-Phillips-Terlevich diagrams show 74% of MAUVE spaxels ionized by sources other than H ii regions versus 61% in the field, and we find these ionization differences to be closely coupled to broadened kinematics. In all, 44% of MAUVE spaxels exceed H alpha sigma(LOS) = 40 km s(-1) (versus 26% in the field), driven mainly by non-star-forming gas with sigma(LOS) between 40 and 80 km s(-1), consistent with enhanced contribution of diffuse ionized gas (DIG). A subdominant tail of 5% of spaxels at sigma(LOS) > 100 km s(-1), largely absent in PHANGS-MUSE (1%), points to shocks or turbulent mixing layers from intracluster interactions. Our results show that environmental quenching primarily suppresses star formation, unveiling DIG as the dominant ionized component in cluster disks. The elevated line ratios and broadened kinematics observed in the MAUVE sample reflect the physical state of the ISM in the absence of vigorous star formation, rather than widespread direct environmental excitation. The observed shock-like emission provides an additional, secondary contribution likely driven by active interactions with the intracluster medium.

Although globally integrated studies often find that, at fixed stellar mass, high star formation rate (SFR) galaxies are relatively metal-poor while lower SFR systems are more metal-rich, the corresponding coupling between gas-phase metallicity (Z(gas)) and star formation on sub-galactic scales remains poorly constrained. In this study, we analyse 14 Virgo spiral galaxies from the MAUVE-MUSE (Multiphase Astrophysics to Unveil the Virgo Environment with MUSE) survey to revisit the resolved mass-metallicity relation (rMZR) and its secondary dependence on SFR surface density (Sigma(SFR)) at similar to 100 pc scales. We construct cospatial maps of stellar mass surface density (Sigma(*)), Sigma(SFR) and gas-phase oxygen abundance. MAUVE-MUSE galaxies follow a standard rMZR, but once binned in Sigma(*), we find a clear mass-dependent inversion in the Z(gas)-Sigma(SFR) relation with O3N2-based metallicity calibrations: the commonly reported anticorrelation is confined to low-Sigma(*) bins, whereas high-Sigma(*) regions show a positive correlation, with an inversion point at log(10)(Sigma(*)/M-circle dot kpc(-2)) similar or equal to 7.5-8.0. Both correlated and anticorrelated H II regions can co-exist within the same discs, and the observed mass dependence emerges only when grouping H II spaxels by Sigma(*). We develop a spatially resolved gas-regulator model and show that the observed correlation and anticorrelation between Z(gas) and Sigma(SFR) arise from the competition between star-formation-and gas-supply-driven variability: the sign of the local Z(gas)-Sigma(SFR) relation is set by which of these dominates. This framework can be naturally extrapolated to the integrated scenario, providing a unified explanation for both the resolved and global Z(gas)-SFR relations. However, the presence and strength of the Z(gas)-Sigma(SFR) (anti)correlation depend strongly on the metallicity indicator used, highlighting the challenge of disentangling physical secondary trends within metallicity scaling relations.

We augment the published optical photometry of ultra-diffuse galaxy candidates in the SMUDGes catalog with UV and IR measurements to investigate the recent (<1 Gyr) star formation history of 966 galaxies. We find that 1) we classify star forming, post-starforming, and quenched galaxies with a precision that is comparable to that of spectroscopic studies, 2) the star forming systems are sub-normally efficient and would not have formed their current stellar mass at their current star formation rate over a Hubble time, 3) the sample is biased against more strongly star forming systems by the central surface brightness criterion of ultra-diffuse galaxies, 4) for galaxies that are not quenched, the timescale of star formation episodes in this sample is typically ≲ 1 Gyr, 5) post-starburst galaxies in the sample tend to be of lower stellar mass and star forming galaxies of higher stellar mass, suggesting that the star forming behavior of these galaxies does depend on mass, and 6) there is a marginal indication, with caveats, that star formation episodes increase galaxy size, as measured by the half-light radius, by about 8%. In addition to providing a statistically-sized sample with which to explore the star formation behavior of these galaxies, this study also provides a way to select galaxies with specific recent star formation histories for spectroscopic follow-up.

We present the spatial part of the point source signal extraction strategy for the upcoming CHORD galaxy survey. CHORD, the Canadian Hydrogen Observatory and Radio-transient Detector, is an under-construction drift-scanning compact interferometric radio telescope. CHORD comprises 512 six meter dishes and observes in the 300 to 1500 MHz frequency range. One of its science goals is producing a catalogue of galaxies detected by the neutral hydrogen (HI) 21 cm emission line. CHORD's highly redundant dish layout creates the problem of spatial aliasing, the effect where the same signal could be feasibly produced from sources at multiple locations on the sky. The search will be done with a matched filter in the visibility plane. This paper presents the search strategy and a prediction tool that can quickly estimate the matched filter response at a given sky position, allowing a prediction of alias locations and severity. This tool confirms that although aliases are impossible to distinguish in a single snapshot, they become possible to distinguish when combining data over a period of time. It predicts that aliases will be harder to distinguish for observations closer to the celestial equator, but that scanning with offset adjacent strips can remove this degeneracy. It predicts that the optimal strategy for a single offset to disambiguate aliases is to re-point the array in declination by about two degrees. A future paper will combine these findings with realistic noise estimates and galaxy population statistics to make forecasts of the population of galaxies that CHORD will detect.

We present new ASKAP/WALLABY HI observations of the nearby dwarf galaxy system ESO 179-013 (Kathryn's Wheel), the nearest known collisional ring galaxy, located 10 Mpc away in the Local Void. The system is composed of three previously known dwarf galaxies embedded in a large HI envelope, with a newly discovered fourth member identified through HI and radio continuum emission behind a bright foreground binary. Galaxy D exhibits the highest star formation rate in the group and deviates from the HI mass-diameter relation, suggesting it is a compact, gas-rich dwarf missed due to stellar foreground contamination. The HI data reveal for the first time an extended HI envelope around the whole system, the neutral gas counterpart of the star-forming ring and gas bridges among members, suggesting a more complex interaction history than the previously proposed collisional ring scenario. ESO 179-013 thus provides a rare opportunity to study hierarchical assembly and gas dynamics in underdense environments and demonstrates the power of blind HI surveys in identifying faint members of low-mass compact groups.

We present results from our ongoing campaign to follow up the satellite candidates from the Identifying Dwarfs of MC Analog GalaxiEs (ID-MAGE) survey. Previously, we published a list of 355 unresolved satellite candidates identified around 36 nearby LMC- and SMC-mass hosts (D=4-10 Mpc). We present the velocities of 83 satellite candidates from new Green Bank Telescope observations, optical long-slit spectra, and the Dark Energy Survey Instrument Data Release 1. Based on their velocities, we identify six candidates as probable satellite galaxies (6.5×10^5≤ M_⋆/M_⊙≤1.5×10^7) and 77 as background galaxies. Our results underscore the ability of spectroscopic follow-up to effectively separate satellites from background galaxies. Using the refined sample, we update our previously derived estimates for the average satellite population per host and find 1.7±0.7 (1.0±0.3) satellites per LMC-mass (SMC-mass) host. Our current satellite sample includes 25 galaxies confirmed by distances or velocities. This set includes the complete satellite populations of three hosts (UGC 04422: zero satellites, UGC 08201: zero satellites, NGC 3432: four satellites), which we compare to simulations and known satellite systems from the literature. Our sample is nearly complete for the most massive satellites (M_⋆ > 10^7 M_⊙). We find these massive satellites have a quenched fraction of 10–25%, placing them between the <5% quenched fraction of isolated galaxies and the 40–70% quenched fraction of MW-analog satellites with 10^7 M_⊙ < M_⋆ < 10^8 M_⊙. This demonstrates the impact that low-mass galaxies have on the evolution of their satellites.

The baryonic Tully-Fisher relation (bTFR) and the radial acceleration relation (RAR) link the observed dynamics in galaxies to that expected from their baryonic mass distributions. The relations' small intrinsic scatters place strong constraints on galaxy formation models, dark matter properties and theories of modified dynamics, yet detailed measurements beyond the very local Universe remain limited. We use 130 purely HI-selected galaxies with resolved HI kinematics and baryonic mass profiles to measure the bTFR and RAR up to z≈0.09. We measure a tight RAR with an acceleration scale a_0=(1.50±0.05)×10^-10, m,s^-2 and an intrinsic scatter of 0.096±0.006 dex, consistent with local results. We fit the bTFR in the `inverse' direction, conditioning on M_ bar to mitigate HI flux-related selection effects, measuring a logarithmic slope of 0.27±0.01 (corresponding to a forward slope of 3.72±0.16), with vertical intrinsic scatter σ_⊥≈0.05 dex. Fitting the general δ-family of MOND interpolating functions to the RAR, we infer δ=4.10^+1.4_-0.68, consistent with the value required by Solar System gravitational constraints and a null Wide Binary Test. We find no significant redshift evolution in the RAR acceleration scale for our pure HI-selected sample. However, the bTFR zero-point shows an apparent evolutionary trend that is strongly dependent on the fit direction: the traditional forward fit yields an 8.7σ preference for z evolution, while for our fiducial inverse fit, this reduces to 3.4σ, within ≈2σ of the RAR evolution constraint. This suggests selection effects bias the forward fit; a careful consideration of such effects will be required in future endeavours to robustly measure the redshift evolution of dynamical scaling relations.

The rapid quenching of satellite galaxies in dense environments is often attributed to environmental processes such as ram pressure stripping. However, stripping alone cannot fully account for the removal of dense, star-forming gas in many satellites, particularly in their inner regions. Recent models and indirect observations have suggested that star-formation-driven outflows may play a critical role in expelling this remaining gas, yet direct evidence for such feedback-driven quenching remains limited. Here we report the discovery of an ionized gas outflow in NGC 4064, a Virgo cluster satellite that has already lost most of its cold gas through environmental stripping. MUSE observations from the Multiphase Astrophysics to Unveil the Virgo Environment survey reveal a bipolar outflow driven by residual, centrally concentrated star formation in NGC 4064—despite its current star formation rate being ∼0.4 dex below the star-forming main sequence due to prior interaction with the cluster environment. The outflow’s mass loading factor is ∼2, suggesting that stellar feedback could remove the remaining gas on timescales shorter than those required for depletion by star formation alone. These results demonstrate that even modest but centrally concentrated star formation can drive efficient feedback in stripped satellites, accelerating quenching in the final stages of their evolution.

Neutral atomic hydrogen plays a central role in the evolution of galaxies. Yet our understanding of how gas is accreted onto galactic disks, and the way this is governed by the cascade of processes extending up to cosmic web scales, remains poorly understood. The Square Kilometre Array has the potential to significantly advance our understanding in this field, being able to both resolve galactic disks with high column density sensitivity, while also being able to survey the large volumes needed to understand the impact of processes at the level of the cosmic web. In this chapter, we examine recent observational and theoretical progress made in this area, the potential contribution of the SKA, and needed alignment with other radio and multiwavelength facilities to advance the field.

We investigate the relation between neutral atomic hydrogen (Hi) and dark matter halo mass (HIHM) using observations from the Deep Investigation of Neutral Gas Origins (DINGO) pilot survey 100 h data, combined with spectroscopic data from the Galaxy and Mass Assembly (GAMA) survey and photometric data from the Wide Area VISTA Extragalactic Survey (WAVES) photometric catalogue. We employ a combination of direct detections and spectral stacking to probe the Hi content of haloes across a wide mass range ( 10(10 . 5) less than or similar to M-h/M-(R) less than or similar to 10(14 . 5 )). By incorporating WAVES photometric members on top of the existing GAMA group catalogue, we present a novel approach of extending stacking analyses beyond spectroscopic completeness limits, enabling recovery of satellite Hi content otherwise missed. We find that the HIHM relation exhibits a double power-law form, with a turnover near Mh similar to 1011.2 M (R). Central galaxies dominate the halo Hi budget below M-h similar to 6 x 10(12 )M ((R)), while satellites dominate at higher halo masses. Including photometric members increases the measured Hi content in haloes above 10(13) M ((R)) by a factor of 1.5-3, highlighting the importance of gas-rich satellites in the group and cluster regime. Comparison with previous group-stacking studies shows that low-surface brightness galaxies and intra-group Hi structures contribute only a minor fraction to the total H i mass in group and cluster haloes, as the summed galaxy Hi masses are consistent with the total halo H i content.

Population studies of gas-rich galaxies across the full range of Neutral Hydrogen (HI) masses that galaxies are known to exhibit (10^5 ≲ M_HI≲ 10^11 M_⊙) remain limited by the need to conduct high-sensitivity, wide-band surveys across significant sky areas. The Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) is a next-generation radio telescope that will significantly expand the census of HI-galaxies to date from untargeted drift-scan surveys at declinations +20^∘ < δ< +80^∘. We draw survey realizations from a known HI mass function (HIMF) to forecast HI detections in fiducial 1-year and 5-year CHORD surveys. The 5-year survey source counts is expected exceed currently available catalogs by roughly an order of magnitude, notwithstanding the potential impacts of radio frequency interference (RFI) and spectroscopic source confusion that we also estimate. We predict that CHORD will push the low-mass HI galaxy census to M_HI∼ 10^5.5 M_⊙, over an order of magnitude lower than has been previously achieved. At the high mass end of the HIMF, CHORD is expected to detect ∼10^3 massive gas-rich giants (M_HI≳ 10^10.5 M_⊙) at 0.3 ≲ z ≲ 0.5, which will explore the evolution of this population relative to local universe estimates. CHORD HI surveys will therefore improve our understanding of the neutral gas reservoirs at the low-mass and high-mass extremes of the galaxy population.

Understanding the nature of dark matter (DM) is one of the most pressing questions of modern physics. The flat rotation curves of galaxies, especially the extended HI rotation curves from radio observations at 21 cm, played a key historical role to establish the DM problem and continue to be a major tool to test different galaxy formation models, particle DM models, and modified gravity theories. The SKA observatory will revolutionize the study of HI rotation curves thanks to its unprecedented angular resolution, sensitivity, and survey speed. In combination with optical and near-infrared ancillary data, HI surveys with SKA-Mid AA4 will allow us to (1) obtain HI data at spatial resolutions of 1"-2", probing the inner galaxy dynamics with unprecedented details (e.g., the cusp-core problem); (2) move from representative samples of a few hundreds of objects to statistical samples of tens of thousands of objects, allowing us to study the dynamical scaling laws of galaxies and their DM properties with unprecedented statistical power across different cosmic environments; (3) move from galaxies at z 0 to galaxies at z 1, probing DM halos at earlier cosmic epochs and exploring the redshift evolution of the dynamical laws across about 8 Gyrs. The massive SKA data, however, will pose important technical challenges for the derivation of HI rotation curves with automated kinematic software. Developing such kinematic software in the SKA era will be crucial to reach major scientific goals, such as discriminating between different solutions to the DM problem.

We investigate the relation between neutral atomic hydrogen (HI) and dark matter halo mass (HIHM) using observations from the Deep Investigation of Neutral Gas Origins (DINGO) pilot survey 100h data, combined with spectroscopic data from the Galaxy and Mass Assembly (GAMA) survey and photometric data from the Wide Area VISTA Extragalactic Survey (WAVES) photometric catalog. We employ a combination of direct detections and spectral stacking to probe the HI content of halos across a wide mass range (10^10.5≲ M_h/M_⊙≲ 10^14.5). By incorporating WAVES photometric members on top of the existing GAMA group catalog, we present a novel approach of extending stacking analyses beyond spectroscopic completeness limits, enabling recovery of satellite HI content otherwise missed. We find that the HIHM relation exhibits a double power-law form, with a turnover near M_h∼ 10^11.2 M_⊙. Central galaxies dominate the halo HI budget below M_h∼ 6 × 10^12 M_⊙, while satellites dominate at higher halo masses. Including photometric members increases the measured HI content in halos above 10^13 M_⊙ by a factor of 1.5-3, highlighting the importance of gas-rich satellites in the group and cluster regime. Comparison with previous group-stacking studies shows that low-surface brightness galaxies, and intra-group HI structures contribute only a minor fraction to the total HI mass in group and cluster halos, as the summed galaxy HI masses are consistent with the total halo HI content.

The Canadian Hydrogen Observatory and Radio-transient Detector (CHORD) is a next-generation wideband radio interferometer currently being constructed and commissioned at the Dominion Radio Astrophysical Observatory in British Columbia, Canada. CHORD is designed for precision 21 cm cosmology, fast radio transient discovery, spectral line galaxy surveys, and pulsar science using a highly redundant large-N, small-diameter drift-scan array architecture. The telescope consists of a 512-element core array of 6 m dishes operating from 300–1500 MHz in drift-scan mode, together with two 64-dish outrigger stations located at the Hat Creek Radio Observatory and the Green Bank Observatory for long-baseline transient localization. The instrument supports multiple simultaneous digital backends for interferometric correlation, FRB detection, pulsar beamforming, and high spectral resolution surveys. CHORD is designed with an emphasis on precision beam control and stable instrumental response, incorporating lessons learned from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) while providing a substantial increase in sensitivity. Initial performance has been evaluated using a three-dish engineering array, and a 64-dish pathfinder array is currently being commissioned. The full array will be commissioned in 2028.

We present deep, wide-field Magellan/Megacam imaging of the ultra-faint Milky Way (MW) satellites Grus II (Gru II) and Horologium II (Hor II), with the aim of deriving improved constraints on their distances, luminosities, and structural parameters, while also searching for possible signs of tidal disturbance. Our photometry reaches approximately 3 magnitudes deeper than the discovery data, enabling robust measurements of these quantities. Both systems exhibit color-magnitude diagrams consistent with old (∼12.5 Gyr), very metal-poor stellar populations. We find Gru II to be at a distance of 52.3 ± 1.9 kpc, with a half-light radius of 6.8 ± 0.5 arcmin (103 ± 9 pc), ellipticity ε= 0.25 ± 0.07, and absolute magnitude M_V = -4.07 ± 0.50 mag. Hor II is further away at a distance of 72.4^+5.9_-5.5 kpc and more compact, with r_h = 2.1 ± 0.2 arcmin (44^+6_-5 pc), ε= 0.32^+0.20_-0.16, and M_V = -2.10 ± 0.44 mag. Both galaxies lie within the typical size-luminosity locus of MW ultra-faint dwarfs. Gru II shows an asymmetric morphology including multi-directional clumpy features, some of which may be suggestive of tidal disturbance. We further identify and spectroscopically confirm a new distant member just outside 3r_h in Gru II, providing independent evidence for member stars at large projected radii. In contrast, Hor II appears regular, with no significant extended structure detected to the surface-brightness limits of our data.