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

Abstract

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 (H i) 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 H i data, we study the H i and molecular gas within the optical discs of Virgo cluster galaxies on 1.2-kpc scales with spatially resolved scaling relations between stellar ( $\Sigma_{\star}$ ), H i ( $\Sigma_{\text{H}\,{\small\text{I}}}$ ), and molecular gas ( $\Sigma_{\text{mol}}$ ) surface densities. Adopting H i deficiency as a measure of environmental impact, we find evidence that, in addition to removing the H i at large radii, the cluster processes also lower the average $\Sigma_{\text{H}\,{\small\text{I}}}$ of the remaining gas even in the central $1.2\,$ kpc. The impact on molecular gas is comparatively weaker than on the H i, and we show that the lower $\Sigma_{\text{mol}}$ gas is removed first. In the most H i-deficient galaxies, however, we find evidence that environmental processes reduce the typical $\Sigma_{\text{mol}}$ of the remaining gas by nearly a factor of 3. We find no evidence for environment-driven elevation of $\Sigma_{\text{H}\,{\small\text{I}}}$ or $\Sigma_{\text{mol}}$ in H i-deficient galaxies. Using the ratio of $\Sigma_{\text{mol}}$ -to- $\Sigma_{\text{H}\,{\small\text{I}}}$ 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.

VERTICO. VII. Environmental Quenching Caused by the Suppression of Molecular Gas Content and Star Formation Efficiency in Virgo Cluster Galaxies

“…At face value we appear to contradict the result of Watts et al (2023) who find no evidence for environment-driven increases in molecular gas densities in VERTICO galaxies. However, Watts et al (2023) are comparing much coarser subsets of the VERTICO galaxies divided into three bins of H I deficiency. Figure 5 demonstrates that the increase in gas densities due to ram pressure is only apparent in the earliest stage of stripping identified by the Yoon et al (2017) morphology and phasespace analysis.…”

“…In this section, we present the VERTICO rSFMS-the first such characterization of this relationship for cluster galaxiesand study the VERTICO rMGMS and rKSR first published in Watts et al (2023) andJiménez-Donaire et al (2023), respectively.…”

“…Most commonly, field control samples are constructed to match the target galaxy in either the size or mass of the stellar disk Chung et al 2009;Zabel et al 2022). There are a number of studies demonstrating the efficacy of H I deficiency as a tracer of environmental influence, both for cluster galaxies in general (e.g., Li et al 2020) and the specific galaxies studied in this work (e.g., Yoon et al 2017;Zabel et al 2022;Watts et al 2023). For an extensive discussion of H I deficiency, including the respective merits of the various definitions, we refer the reader to Section 3 of Cortese et al (2021).…”

“…Although less well studied than the rKSR, a growing number of works have established a correlation between molecular gas and stellar surface densities-known as the resolved molecular gas main sequence (rMGMS)-which governs the amount of gas available for star formation (Lin et al 2019;Morselli et al 2020;Ellison et al 2021;Pessa et al 2021). The presence of the rMGMS in cluster members was recently established by Watts et al (2023) who show that the individual cluster galaxy rMGMS gradually moves below the field relation as H I deficiency increases.…”

The Evolution of the Cold Gas Fraction in Nearby Clusters’ Ram-pressure-stripped Galaxies

“…Although our results are derived from single-dish observations, which do not possess the spatial resolution needed to disentangle the impact of the ram pressure on the galaxy disks (as done in Virgo by Watts et al 2023 and in GASP galaxies with ALMA data in Moretti et al 2020aMoretti et al , 2020b, they still provide a first consistent view on the evolution of the cold gas reservoir in a statistically significant sample of galaxies subject to this environmental effect.…”