From Stellar Nurseries to Old Stellar Populations: A Multi-wavelength Case of NGC 1055
Monthly notices of the Royal Astronomical Society 531:3 (2024) 3103–3117
Abstract:
Given the complex nature of galaxies’ interstellar medium (ISM), multi-wavelength data are required to probe the interplay among gas, dust, and stellar populations. Spiral galaxies are ideal laboratories for such a goal as they are rich in gas and dust. Using carbon monoxide (CO) along with GALEX far-ultraviolet (FUV) and Spitzer near-infrared (NIR) data we probe the correlations amongst the properties of stellar populations, gas, and dust over the disc of the spiral galaxy NGC 1055 at multiple angular resolutions, i.e. 2, 4, and 17 arcsec corresponding to a linear size of 144 pc, 288 pc, and 1.2 kpc, respectively. Our results indicate an asymmetry in the physical conditions along the galaxy’s disc, i.e. the gas is slightly more extended and brighter, and molecular gas mass is higher on the disc’s eastern side than the western side. All physical properties (i.e. molecular gas mass, CO line ratios, stellar mass, NIR emission) decrease from the centre going outwards in the disc with some exceptions (i.e. the extinction, FUV radiation, and the [3.6]−[4.5] colour). Our analysis indicates that the colour gets bluer (metallicity increases) halfway through the disc, then redder (metallicity decreases) going outwards further in the disc.
Erratum: “The Evolution of NGC 7465 as Revealed by Its Molecular Gas Properties” (2021, ApJ, 909, 98)
The Astrophysical Journal American Astronomical Society 937:1 (2022) 47-47
Down but not out: properties of the molecular gas in the stripped Virgo Cluster early-type galaxy NGC4526
The Astrophysical Journal, 933:1 (2022) 90-119
Abstract:
We present Atacama Large Millimeter/submillimeter Array data on the 3 mm continuum emission, CO isotopologues (12CO, 13CO, and C18O), 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/H2 conversion factors, are similar to those found in nearby spirals. One striking exception is the very low observed 12CO/13CO(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 [12CO/13CO] abundance ratios of 7.8 and 6.5 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 [13CO/C18O]. More detailed chemical evolution modeling would be interesting in order to explore whether the unusual [12CO/13CO] 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
Astrophysical Journal IOP Science 909:2 (2021) 98
Abstract:
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 12CO/13CO line ratios in its nucleus but typical 13CO/C18O ratios. Our calculations show that this result does not necessarily indicate an unusual [12CO/13CO] abundance ratio but rather that 12CO (1-0) is optically thin due to high temperatures and/or large linewidths 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.Molecular gas kinematics and line diagnostics in early-type galaxies: NGC4710 & NGC5866
Monthly Notices of the Royal Astronomical Society Oxford University Press 463:4 (2016) 4121-4152