VERTICO: VI: Cold-gas asymmetries in Virgo cluster galaxies
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abstract
We analyse cold-gas distributions in Virgo cluster galaxies using resolved observations of CO(2-1), which traces molecular hydrogen (H2), and H I from the Virgo Environment Traced In CO (VERTICO) and 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 divided our Virgo galaxy sample into H I-normal, H I-tailed, and H I-truncated classes and show, unsurprisingly, that the H I-tailed galaxies have the largest quantitative H I asymmetries. We also compared Virgo galaxies to a control sample of non-cluster galaxies and find that the former, on average, have H I asymmetries that are 40 ± 10% larger than the latter. There is less separation between control, H I-normal, H I-tailed, and H I-truncated galaxies in terms of H2 asymmetries, and on average, Virgo galaxies have H2 asymmetries that are only marginally (20 ± 10%) larger than the control sample. We find a weak correlation between H I and H2 asymmetries over our entire sample, but a stronger correlation for the galaxies that are strongly impacted by environmental perturbations. Finally, we divided the discs of the H I-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 is accompanied by an excess in the star formation rate such that the depletion time is, on average, unchanged.
