Browsing by Author "Young, Lisa M."

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Down but Not Out: Properties of the Molecular Gas in the Stripped Virgo Cluster Early-Type Galaxy Ngc 4526
(Iop Publishing Ltd, 2022) Young, Lisa M.; Meier, David S.; Crocker, Alison; Davis, Timothy A.; Topal, Selcuk
We present Atacama Large Millimeter/submillimeter Array data on the 3 mm continuum emission, CO isotopologues ((CO)-C-12, (CO)-C-13, and (CO)-O-18), and high-density molecular tracers (HCN, HCO+, HNC, HNCO, CS, CN, and CH3OH) in NGC 4526. These data enable a detailed study of the physical properties of the molecular gas in a longtime resident of the Virgo Cluster; comparisons to more commonly studied spiral galaxies offer intriguing hints into the processing of molecular gas in the cluster environment. Many molecular line ratios in NGC 4526, along with our inferred abundances and CO/H-2 conversion factors, are similar to those found in nearby spirals. One striking exception is the very low observed (CO)-C-12/(CO)-C-13(1-0) line ratio, 3.4 +/- 0.3, which is unusually low for spirals though not for Virgo Cluster early-type galaxies. We carry out radiative transfer modeling of the CO isotopologues with some archival (2-1) data, and we use Bayesian analysis with Markov Chain Monte Carlo techniques to infer the physical properties of the CO-emitting gas. We find surprisingly low [(CO)-C-12/(CO)-C-13] abundance ratios of 7.8(-1.5)(+2.7) and 6.5(-1.3)(+3.0) at radii of 0.4 kpc and 1 kpc. The emission from the high-density tracers HCN, HCO+, HNC, CS, and CN is also relatively bright, and CN is unusually optically thick in the inner parts of NGC 4526. These features hint that processing in the cluster environment may have removed much of the galaxy's relatively diffuse, optically thinner molecular gas along with its atomic gas. Angular momentum transfer to the surrounding intracluster medium may also have caused contraction of the disk, magnifying radial gradients such as we find in [(CO)-C-13/(CO)-O-18]. More detailed chemical evolution modeling would be interesting in order to explore whether the unusual [(CO)-C-12/(CO)-C-13] abundance ratio is entirely an environmental effect or whether it also reflects the relatively old stellar population in this early-type galaxy.
The Evolution of Ngc 7465 as Revealed by Its Molecular Gas Properties
(Iop Publishing Ltd, 2021) Young, Lisa M.; Meier, David S.; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; Topal, Selcuk
We present ALMA observations of CO isotopologues and high-density molecular tracers (HCN, HCO+, CN, etc.) in NGC 7465, an unusually gas-rich early-type galaxy that acquired its cold gas recently. In the inner 300 pc, the molecular gas kinematics are misaligned with respect to all other galaxy components; as the gas works its way inward, it is torqued into polar orbits about the stellar kinematically decoupled core (KDC), indicating that the stellar KDC is not related to the current gas accretion event. The galaxy also exhibits unusually high (CO)-C-12/(CO)-C-13 line ratios in its nucleus but typical (CO)-C-13/(CO)-O-18 ratios. Our calculations show that this result does not necessarily indicate an unusual [(CO)-C-12/(CO)-C-13] abundance ratio but rather that (CO)-C-12 (1-0) is optically thin due to high temperatures and/or large line widths associated with the inner decoupled, misaligned molecular structure. Line ratios of the higher-density tracers suggest that the densest phase of molecular gas in NGC 7465 has a lower density than is typical for nearby galaxies, possibly as a result of the recent gas accretion. All of the observed molecular properties of NGC 7465 are consistent with it having acquired its molecular (and atomic) gas from a spiral galaxy. Further detailed studies of the CO isotopologues in other early-type galaxies would be valuable for investigating the histories of those that may have acquired their gas from dwarfs. Finally, these ALMA data also show an unidentified line source that is probably a background galaxy similar to those found at z = 1-3 in blind CO surveys.
The Evolution of Ngc 7465 as Revealed by Its Molecular Gas Properties (Vol 909, 98, 2021)
(Iop Publishing Ltd, 2022) Young, Lisa M.; Meier, David S.; Bureau, Martin; Crocker, Alison; Davis, Timothy A.; Topal, Selcuk