arXiv subjects

Toby Brown

Publications and source records attributed to Toby Brown.

At least 19 recordsLinked to original sources

arXiv2026

The Next Generation Virgo Cluster Survey (NGVS). II. A Catalog of Galaxies in the Virgo Cluster

The Next Generation Virgo Cluster Survey (NGVS) is a deep, high resolution imaging campaign that used the 1 deg$^2$ MegaCam instrument on the Canada-France-Hawaii Telescope to carry out a comprehensive optical survey of the Virgo cluster, from its core to its virial radius. The NGVS covers a contiguous area of 104 deg$^2$ (8.63 Mpc$^2$ at the 16.5 Mpc distance of Virgo) in the $u^*$-,$g$-,$i$-, and $z$-band, with additional limited coverage in $r$. In this paper, we present the final catalog of Virgo galaxies across the entire NGVS area. The catalog includes 3680 galaxies considered to be $bona~fide$ members of the cluster, spanning a factor of 2.5 million in luminosity, from $g = 8.42$ mag to $g = 24.41$ mag ($M_g = -22.67$ mag to $M_g = -6.68$ mag). With 2100 previously uncataloged galaxies, the NGVS catalog augments the number of known Virgo members by a factor 2.3. The catalog is complete down to $g = 18.6$ mag ($M_g=-12.5$ mag, corresponding to a stellar mass $M_* \sim 1.6\times10^7~M_{\odot}$ for an old stellar population) and 50% complete at $g = 22.0$ mag ($M_g=-9.1$ mag, $M_* \sim 6.2\times10^5~M_{\odot}$), three magnitudes deeper than the venerable Virgo Cluster Catalog (VCC), which for over 40 years has served as the reference standard for Virgo. Photometric and structural parameters are derived for all NGVS galaxies and presented in a series of tables, alongside nuclear and morphological classification, as well as stellar masses and, when available, radial velocities.

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arXiv2026

MAUVE-MUSE: When Metallicity Follows or Fights Star Formation -- A Mass-Dependent Inversion in Virgo Galaxies

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 ($Z_{\rm gas}$) and star formation on sub-galactic scales remains poorly constrained. In this study, we analyse 14 Virgo spirals from the MAUVE-MUSE survey to revisit the resolved mass-metallicity relation (rMZR) and its secondary dependence on SFR surface density ($\Sigma_\mathrm{SFR}$) at $\sim 100$\,pc scales. We construct co-spatial maps of stellar mass surface density ($\Sigma_*$), $\Sigma_\mathrm{SFR}$, and oxygen abundance. MAUVE-MUSE galaxies follow a standard rMZR, but when binned by $\Sigma_*$, we find a mass-dependent inversion in the $Z_\mathrm{gas}$-$\Sigma_\mathrm{SFR}$ relation using O3N2 calibrations: the standard anti-correlation is confined to low-$\Sigma_*$ bins, while high-$\Sigma_*$ regions show a positive correlation, inverting at $\log_{10}(\Sigma_*/M_\odot\,\mathrm{kpc}^{-2})\simeq 7.5$-8.0. Correlated and anti-correlated \ion{H}{ii} regions coexist within the same discs; the mass dependence emerges only when grouping spaxels by $\Sigma_*$. We develop a spatially resolved gas-regulator model showing this $Z_\mathrm{gas}$-$\Sigma_\mathrm{SFR}$ (anti-)correlation arises from competition between star-formation-driven and gas-supply-driven variability. This framework naturally extrapolates to the integrated scenario, providing a unified explanation for resolved and global relations. However, the presence and strength of the $Z_\mathrm{gas}$-$\Sigma_\mathrm{SFR}$ (anti-)correlation depend strongly on the metallicity indicator used, highlighting the challenge of disentangling physical secondary trends within metallicity scaling relations.

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arXiv2026

MAUVE-MUSE: Ionization and Kinematic Signatures of Environmental Effects on Virgo Cluster Disks

We present early science results from the MAUVE (Multiphase Astrophysics to Unveil the Virgo Environment) program which targets 40 Virgo Cluster galaxies to investigate the effect of environment on the interstellar medium (ISM) at ~100 pc scales. From 12 galaxies in the MAUVE-MUSE early sample, we find systematically elevated line ratios compared to PHANGS-MUSE field disks, with higher medians of [N II]/H$\alpha$ (0.75 vs. 0.50), [S II]/H$\alpha$ (0.57 vs. 0.49), and [O III]/H$\beta$ (1.04 vs. 0.68). Spatially resolved BPT diagrams show 74% of MAUVE-MUSE 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. 44% of MAUVE-MUSE spaxels exceed H$\alpha$ $\sigma_{LOS} = 40$ km/s (vs. 26% in the field), driven mainly by non-star-forming gas with $\sigma_{LOS}$ between 40 and 80 km/s, consistent with enhanced contribution of diffuse ionized gas (DIG). A subdominant tail of 5% of spaxels at $\sigma_{LOS} > 100$ km/s, 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.

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arXiv2026

WALLABY pilot survey: HI depletion times within the stellar discs of nearby galaxies

Neutral atomic hydrogen (HI) reservoirs typically extend far beyond the inner star-forming regions of galaxies, and global HI measurements, which mix these distinct environments, limit our understanding of the gas-star formation cycle. In particular, global HI depletion times combine gas and star formation from different physical scales, contributing to long measured timescales (5-9 Gyr) and large scatter compared to molecular gas. Using 841 gas-rich galaxies from the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) pilot observations, we investigate how HI depletion time and its scaling relations change when HI and star formation are both confined to the stellar disc (R25, the isophotal radius at 25 mag arcsec-2 in i-band). We find that depletion times within this region are on average 1.4 Gyr shorter than global values, though some remain very long, indicating that a substantial fraction of HI remains inactive for star formation. HI depletion times anti-correlate strongly with stellar surface density, and this trend becomes even tighter within the stellar disc. The Kennicutt-Schmidt relation further reveals an almost constant HI depletion time at fixed stellar surface density, similar to the behaviour seen for molecular gas, suggesting that HI and star formation are regulated by conditions that enable HI-to-H2 conversion, traced by stellar surface density. Beyond the stellar disc, HI depletion times are on average almost 10 Gyr longer than within R25, confirming extremely inefficient star formation in low-density outer regions. These results highlight the critical role of spatial location and local conditions for HI to serve as a fuel for star formation.

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arXiv2026

EMBERS I: Low redshift post-starburst galaxies are frequently depleted in molecular gas relative to star forming progenitors

The cold gas content of post-starburst galaxies (PSBs) provides important insight into the mechanisms that drive rapid quenching, but a multiphase assessment of both the atomic and molecular gas in PSBs does not yet exist. We introduce the Ensemble of Multiphase Baryons Evolving in Rapidly-quenching Systems, or EMBERS, a homogeneously selected, nearly mass- and redshift-complete survey of the global atomic (HI) and molecular gas (H2) in PSBs, observed with the Five Hundred-metre Aperture Spherical Telescope (FAST) and the Institut de radioastronomie millimetrique (IRAM) 30m telescope. We present new CO(1-0) observations for 52 PSBs with the IRAM 30m, which, combined with 9 archival observations, gives a total H2 sample of 61, of which 58/61 have ancillary HI measurements. We detect CO(1-0) in 34/61 galaxies, corresponding to molecular gas fractions (fH2 = MH2/M*) ranging from two to 250 per cent. By comparing with a stellar-mass matched star-forming (SF) control sample from xCOLD GASS, we find that PSBs on average are 0.3-0.6 dex depleted in H2. However, considering both HI and H2, individual PSBs host diverse gas reservoirs ranging from gas-rich in both phases, elevated in one phase, or gas-poor, the latter of which is common at lower stellar mass. The existence of gas-normal and gas-depleted PSBs in both phases suggests that some PSBs may rejuvenate their star formation, but the rapid shutdown of star formation in others is likely terminal. Despite this diversity, the majority of EMBERS PSBs are gas-poor compared to SF controls, with the typical PSB hosting gas reservoirs intermediate to those found in star-forming and quenched galaxies.

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arXiv2026

The impact of ram pressure on the radio spectral index and magnetic field of NGC 4522: A high-resolution VLA continuum study

We present high-resolution Very Large Array (VLA) continuum observations at S-band ($3$ GHz, $560$ pc scale) and X-band ($10$ GHz, $200$ pc scale) of the ram-pressure-stripped Virgo galaxy NGC 4522, to investigate the characteristics of its radio continuum, spectral index, and magnetic field under the influence of the intracluster medium (ICM). The total radio continuum shows an asymmetry that extends northwest, mirroring the HI gas distribution, but showing distinct features in the extraplanar regions. The spectral index steepens systematically from $\alpha\sim-0.6$ in the main disk to $\alpha\sim-1.1$ in the outer disk. We find that the spectral index behavior of the outer disk is mainly due to an ICM shock that can re-accelerate electrons and a significant reduction of thermal emission. Intriguingly, extraplanar clouds exhibit exceptionally flat spectral indices ($\alpha\sim-0.2$ to $0$), resulting from a combination of significantly enhanced thermal emission and pronounced spectral aging of the non-thermal component. Although some of these regions correlate with H$\alpha$, others do not. We propose that the mixing between the ICM and interstellar medium (ISM) is an alternative mechanism that enhances thermal emission independently of star formation. Polarized continuum emissions are highly asymmetric, preferentially distributed along the ICM wind side, and the polarization fraction increases radially outward from the galactic midplane, indicating that the polarized emission is strongly influenced by the ICM wind. Our results show how and where the ICM substantially affects the ISM, and also demonstrate that high-frequency observations are crucial for analyzing the radio continuum of ram pressure stripping galaxies.

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arXiv2025

MAUVE-MUSE: A Star Formation-driven Outflow Caught in the Act of Quenching the Stripped Virgo Galaxy NGC 4064

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 (MAUVE) survey reveal a bi-polar 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.

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arXiv2025

Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE)

The Multiphase Astrophysics to Unveil the Virgo Environment (MAUVE) project is a multi-facility programme exploring how dense environments transform galaxies. Combining a VLT/MUSE P110 Large Programme and ALMA observations of 40 late-type Virgo Cluster galaxies, MAUVE resolves star formation, kinematics, and chemical enrichment within their molecular gas discs. A key goal is to track the evolution of cold gas that survives in the inner regions of satellites after entering the cluster, and how it evolves across different infall stages. With its high spatial resolution -- probing down to the physical scales of giant molecular cloud complexes -- and multiphase synergy, MAUVE aims to offer a time-resolved view of environmental quenching and set a new benchmark for cluster galaxy studies.

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arXiv2025

SDSS-ALMA Legacy Value Archival Gas Exploration (SALVAGE) -- I: global star formation is governed by central (not global) molecular gas

Star-forming galaxies form tight relations between their stellar mass, star-formation rate, and molecular gas reservoir on global and resolved scales. On the path to quiescence, the exchange between gas and stars must inevitably be broken. Understanding the mechanisms governing star formation and quenching therefore requires observations of both the stellar and molecular gas components. To this end, we have assembled a sample of 277 galaxies ($0.02 \lesssim z \lesssim 0.25$) with semi-resolved optical and millimetre $^{12}$CO(1-0) data, wherein the properties of the inner $\thicksim$2 kpc can be distinguished from the outer regions. This effort was made possible by the Sloan Digital Sky Survey (SDSS) catalogues and the maturing archive of the Atacama Large (sub-)Millimetre Array (ALMA). We call this dataset the SDSS-ALMA Legacy Value Archival Gas Exploration (SALVAGE). In this work, we leverage SALVAGE to provide a semi-resolved perspective on global scaling relations and why some galaxies deviate from them. In agreement with previous work, we find that the offset of a galaxy from the global star-forming main sequence (SFMS) is driven by its inner star formation rate. With the relative inner and outer distributions of molecular gas fraction and star formation efficiency, we investigate whether the central star formation driving global changes is due to fuel availability or efficiency. We find that the position of a galaxy within the SFMS is largely due to the inner star-formation efficiency, while departure from the SFMS is driven by availability of central gas. The central few kpc are thus the most consequential region for galaxy evolution at low redshift.

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arXiv2025

The Next Generation Virgo Cluster Survey (NGVS). XL. The Morphological Classification of Virgo Cluster Galaxies

We present a study of morphologies, based on deep $u^{*}g^{\prime}i^{\prime}z^{\prime}$ imaging of the Virgo Cluster from the Next Generation Virgo Cluster Survey (NGVS), for 3689 Virgo cluster members spanning a mass range of $\sim$$10^{11}M_{\odot}$ to $\sim$$10^5~M_{\odot}$. Our analysis introduces a new, two-component visual classification scheme developed to capture the morphological diversity of galaxies over more than six orders of magnitude in stellar mass. Our morphological classifications use two parameters to describe the global structure and star formation activity of each galaxy. Structural sub-codes denote features such as spiral arms, bars, disks, shells, streams, while star formation sub-codes indicate the form and location of the current star formation activity (e.g., in cores, clumps, filaments, etc). These visual classifications rely on deep $g^\prime$-band images, supplemented by $u^{*}g^{\prime}i^{\prime}$ color images, as well as unsharp-masked images for a subset of objects. We compare our classifications to previous results for bright member galaxies that used more established schemes, finding good agreement. We also measure quantitative classification statistics (e.g., CASGM$_{20}$) for a subset of the brighter galaxies, and present catalogs for some galaxy types of special interest, including structurally compact galaxies, ultra-diffuse galaxies, candidate ultra-compact dwarf transition objects, as well as candidate post-merger systems. These morphological classifications may be useful as a training set in the application of machine learning tools to the next generation of wide-field imaging surveys.

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arXiv2025

VERTICO IX: Signatures of environmental processing of the gas in Virgo cluster spiral galaxies through mapping of CO isotopologues

In this work we study CO isotopologue emission in the largest cluster galaxy sample to date: 48 VERTICO spiral galaxies in Virgo. We show for the first time in a significant sample that the physical conditions within the molecular gas appear to change as a galaxy's ISM is affected by environmental processes. 13CO is detected across the sample, both directly and via stacking, while C18O is detected in a smaller number of systems. We use these data to study trends with global and radial galaxy properties. We show that the CO/13CO line ratio changes systematically with a variety of galaxy properties, including mean gas surface density, HI-deficiency and galaxy morphology. 13CO/C18O line ratios vary significantly, both radially and between galaxies, suggesting real variations in abundances are present. Such abundance changes may be due to star formation history differences, or speculatively even stellar initial mass function variations. We present a model where the optical depth of the molecular gas appears to change as a galaxy's ISM is affected by environmental processes. The molecular gas appears to become more transparent as the molecular medium is stripped, and then more opaque as the tightly bound remnant gas settles deep in the galaxy core. This explains the variations we see, and also helps explain similar observations in cluster early-type galaxies. Next generation simulations and dedicated observations of additional isotopologues could thus provide a powerful tool to help us understand the impact of environment on the ISM, and thus the quenching of galaxies.

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arXiv2025

SYMPHANY- SYnergy of Molecular PHase And Neutral hYdrogen in galaxies in A2626

We present an analysis of the molecular and atomic gas properties of 10 spatially resolved galaxies in the A2626 cluster (z = 0.055), observed as part of the SYMPHANY project. Using CO(2-1) observations from ALMA and SMA, together with HI data from MeerKAT, we examine the interplay between gas phases and environmental influences. A joint morphological and kinematic analysis reveals that while the kinematic behavior of HI and CO are often similar, morphologically the atomic gas is more extended compared to centrally concentrated CO distributions, making it more susceptible to environmental stripping. However, we also find evidence for molecular gas asymmetries, disturbed velocity fields, and H2 deficiencies in some galaxies, indicating that H2 reservoirs can also be disrupted in dense environments. Compared to Virgo-a dynamically unrelaxed, non-cool-core cluster-A2626's relaxed, cool-core structure likely results in less intense ram-pressure stripping. This may allow galaxies to retain more atomic gas, while local interactions or pre-processing may still affect the molecular phase, causing relatively low HI deficiencies but high H2 deficiencies in A2626 galaxies. This is also reflected in the higher gas fractions, slightly elevated SFRs, along with shorter depletion timescales (0.3-3 Gyr), implying moderately enhanced star formation efficiency A2626 galaxies. Moreover, the lack of correlation between H2 deficiency and cluster-centric distance or velocity suggests that molecular gas evolution in A2626 may be shaped more by early infall or local interactions than by current cluster location.

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arXiv2025

Low redshift post-starburst galaxies host abundant HI reservoirs

Studying the gas content of post-starburst (PSB) galaxies can provide valuable clues regarding the process of fast quenching. Although previous works have studied the molecular gas content of PSBs, only a handful of HI measurements exist. Here, we present new Five hundred metre Aperture Spherical Telescope (FAST) 21cm observations of 44 PSBs, leading to 43 detections or sensitive upper limits of HI, which we combine with 25 archival measurements, for a total sample of 68 PSB MHI measurements. HI is detected in 57/68 galaxies, with HI masses ranging from MHI ~10^8.5 up to 10^10 Msun and gas fractions (fHI = MHI/M*) from a few percent up to almost 30 percent. Post-starbursts therefore retain ample atomic gas reservoirs, despite no longer forming stars. By comparing with a stellar mass-matched sample of star-forming galaxies in xGASS, we find that PSBs have, on average, gas fractions lower by ~0.2-0.4 dex, consistent with a mild reduction compared with their progenitor population. However, PSBs show a diversity of HI properties; about half have HI gas masses within the expected scatter of the star-forming population with the remaining 50 per cent up to a factor of 10 more gas-poor. Compared with galaxies in the green valley, about two thirds of PSBs have gas fractions within the expected range, with the remaining third up to a factor of 10 more gas-rich. Our results demonstrate that quenching in PSBs is not the result of wholesale removal of the atomic gas reservoir and that the population has atomic gas fractions that span the range from star-forming to green valley galaxies. We find no correlation between HI gas mass and time since burst; even galaxies a Gyr past their burst can remain HI-normal. The significant gas reservoirs remaining in many PSBs leaves open the possibility for future rekindling of star formation.

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arXiv2024

PHANGS-ML: dissecting multiphase gas and dust in nearby galaxies using machine learning

The PHANGS survey uses ALMA, HST, VLT, and JWST to obtain an unprecedented high-resolution view of nearby galaxies, covering millions of spatially independent regions. The high dimensionality of such a diverse multi-wavelength dataset makes it challenging to identify new trends, particularly when they connect observables from different wavelengths. Here we use unsupervised machine learning algorithms to mine this information-rich dataset to identify novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we extract properties pertaining to their stellar populations; warm ionized and cold molecular gas; and Polycyclic Aromatic Hydrocarbons (PAHs), as measured over 150 pc-scale regions. We show that we can divide the regions into groups with distinct multiphase gas and PAH properties. In the process, we identify previously-unknown galaxy-wide correlations between PAH band and optical line ratios and use our identified groups to interpret them. The correlations we measure can be naturally explained in a scenario where the PAHs and the ionized gas are exposed to different parts of the same radiation field that varies spatially across the galaxies. This scenario has several implications for nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests significant self-regulation in the ISM, (ii) the PAH 11.3/7.7 \mic~ band ratio may be used to constrain the shape of the non-ionizing far-ultraviolet to optical part of the radiation field, and (iii) the varying radiation field affects line ratios that are commonly used as PAH size diagnostics. Neglecting this effect leads to incorrect or biased PAH sizes.

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arXiv2023

VERTICO and IllustrisTNG: The spatially resolved effects of environment on galactic gas

It has been shown in previous publications that the TNG100 simulation quantitatively reproduces the observed reduction in each of the total atomic and total molecular hydrogen gas for galaxies within massive halos, i.e.~dense environments. In this Letter, we study how well TNG50 reproduces the resolved effects of a Virgo-like cluster environment on the gas surface densities of satellite galaxies with $m_* > \! 10^9\,{\rm M}_\odot$ and ${\rm SFR} \! > 0.05\,{\rm M}_\odot\,{\rm yr}^{-1}$. We select galaxies in the simulation that are analogous to those in the HERACLES and VERTICO surveys, and mock-observe them to the common specifications of the data. Although TNG50 does not quantitatively match the observed gas surface densities in the centers of galaxies, the simulation does qualitatively reproduce the trends of gas truncation and central density suppression seen in VERTICO in both HI and H$_2$. This result promises that modern cosmological hydrodynamic simulations can be used to reliably model the post-infall histories of cluster satellite galaxies.

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arXiv2023

VERTICO VII: Environmental quenching caused by suppression of molecular gas content and star formation efficiency in Virgo Cluster galaxies

We study how environment regulates the star formation cycle of 33 Virgo Cluster satellite galaxies on 720 parsec scales. We present the first resolved star-forming main sequence for cluster galaxies, dividing the sample based on their global HI properties and comparing to a control sample of field galaxies. HI-poor cluster galaxies have reduced star formation rate (SFR) surface densities with respect to both HI-normal cluster and field galaxies (0.5 dex), suggesting that mechanisms regulating the global HI content are responsible for quenching local star formation. We demonstrate that the observed quenching in HI-poor galaxies is caused by environmental processes such as ram pressure stripping (RPS) simultaneously reducing molecular gas surface density and star formation efficiency (SFE), compared to regions in HI-normal systems (by 0.38 and 0.22 dex, respectively). We observe systematically elevated SFRs that are driven by increased molecular gas surface densities at fixed stellar mass surface density in the outskirts of early-stage RPS galaxies, while SFE remains unchanged with respect to the field sample. We quantify how RPS and starvation affect the star formation cycle of inner and outer galaxy discs as they are processed by the cluster. We show both are effective quenching mechanisms with the key difference being that RPS acts upon the galaxy outskirts while starvation regulates the star formation cycle throughout disc, including within the truncation radius. For both processes, the quenching is caused by a simultaneous reduction in molecular gas surface densities and SFE at fixed stellar mass surface density.

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arXiv2023

VERTICO VI: Cold-gas asymmetries in Virgo cluster galaxies

We analyze cold-gas distributions in Virgo cluster galaxies using resolved CO(2-1) (tracing molecular hydrogen, H2) and HI observations from the Virgo Environment Traced In CO (VERTICO) and the VLA Imaging of Virgo in Atomic Gas (VIVA) surveys. From a theoretical perspective, it is expected that environmental processes in clusters will have a stronger influence on diffuse atomic gas compared to the relatively dense molecular gas component, and that these environmental perturbations can compress the cold interstellar medium in cluster galaxies leading to elevated star formation. In this work we observationally test these predictions for star-forming satellite galaxies within the Virgo cluster. We divide our Virgo galaxy sample into HI-normal, HI-tailed, and HI-truncated classes and show, unsurprisingly, that the HI-tailed galaxies have the largest quantitative HI asymmetries. We also compare to a control sample of non-cluster galaxies and find that Virgo galaxies, on average, have HI asymmetries that are 40 +/- 10 per cent larger than the control. There is less separation between control, HI-normal, HI-tailed, and HI-truncated galaxies in terms of H2 asymmetries, and on average, Virgo galaxies have H2 asymmetries that are only marginally (20 +/- 10 per cent) larger than the control sample. We find a weak correlation between HI and H2 asymmetries over our entire sample, but a stronger correlation for those specific galaxies being strongly impacted by environmental perturbations. Finally, we divide the discs of the HI-tailed Virgo galaxies into a leading half and trailing half according to the observed tail direction. We find evidence for excess molecular gas mass on the leading halves of the disc. This excess molecular gas on the leading half is accompanied by an excess in star formation rate such that the depletion time is, on average, unchanged.

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arXiv2023

VERTICO V: The environmentally driven evolution of the inner cold gas discs of Virgo cluster galaxies

The quenching of cluster satellite galaxies is inextricably linked to the suppression of their cold interstellar medium (ISM) by environmental mechanisms. While the removal of neutral atomic hydrogen (HI) at large radii is well studied, how the environment impacts the remaining gas in the centres of galaxies, which are dominated by molecular gas, is less clear. Using new observations from the Virgo Environment traced in CO survey (VERTICO) and archival HI data, we study the HI and molecular gas within the optical discs of Virgo cluster galaxies on 1.2-kpc scales with spatially resolved scaling relations between stellar (${\Sigma}_{\star}$), HI (${\Sigma}_\mathrm{HI}$), and molecular gas (${\Sigma}_\mathrm{mol}$) surface densities. Adopting HI deficiency as a measure of environmental impact, we find evidence that, in addition to removing the HI at large radii, the cluster processes also lower the average ${\Sigma}_\mathrm{HI}$ of the remaining gas even in the central 1.2 kpc. The impact on molecular gas is comparatively weaker than on the HI, and we show that the lower ${\Sigma}_\mathrm{mol}$ gas is removed first. In the most HI-deficient galaxies, however, we find evidence that environmental processes reduce the typical ${\Sigma}_\mathrm{mol}$ of the remaining gas by nearly a factor of 3. We find no evidence for environment-driven elevation of ${\Sigma}_\mathrm{HI}$ or ${\Sigma}_\mathrm{mol}$ in HI-deficient galaxies. Using the ratio of ${\Sigma}_\mathrm{mol}$-to-${\Sigma}_\mathrm{HI}$ in individual regions, we show that changes in the ISM physical conditions, estimated using the total gas surface density and midplane hydrostatic pressure, cannot explain the observed reduction in molecular gas content. Instead, we suggest that direct stripping of the molecular gas is required to explain our results.

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