Browsing by Author "Topal, Selcuk"

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Co Tully-Fisher Relation of Star-Forming Galaxies At=0.05-0.3
(Oxford Univ Press, 2018) Topal, Selcuk; Bureau, Martin; Tiley, Alfred L.; Davis, Timothy A.; Torii, Kazufumi
The Tully-Fisher relation (TFR) is an empirical relation between galaxy luminosity and rotation velocity. We present here the first TFR of galaxies beyond the local Universe that uses carbon monoxide (CO) as the kinematic tracer. Our final sample includes 25 isolated, non-interacting star-forming galaxies with double-horned or boxy CO integrated line profiles located at redshifts z <= 0.3, drawn from a larger ensemble of 67 detected objects. The best reverse K-s-band, stellar mass and baryonic mass CO TFRs are, respectively, M-Ks = (-8.4 +/- 2.9)[log (W-50/km s(-1)/sin i) - 2.5] + (-23.5 +/- 0.5), log (M-star/M-circle dot) = (5.2 +/- 3.0)[log (W-50/km s(-1)/sin i) - 2.5] + (10.1 +/- 0.5) and log (M-b/M-circle dot) = (4.9 +/- 2.8)[log (W-50/km s(-1)/sin i) - 2.5] + (10.2 +/- 0.5), where M-Ks is the total absolute K-s-band magnitude of the objects, M-star and M-b their total stellar and baryonic masses, and W-50 the width of their line profile at 50 per cent of the maximum. Dividing the sample into different redshift bins and comparing to the TFRs of a sample of local (z = 0) star-forming galaxies from the literature, we find no significant evolution in the slopes and zero-points of the TFRs since z approximate to 0.3, this in either luminosity or mass. In agreement with a growing number of CO TFR studies of nearby galaxies, we more generally find that CO is a suitable and attractive alternative to neutral hydrogen (HI). Our work thus provides an important benchmark for future higher redshift CO TFR studies.
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
From Stellar Nurseries To Old Stellar Populations: a Multiwavelength Case of Ngc 1055
(Oxford Univ Press, 2024) Topal, Selcuk
Given the complex nature of galaxies' interstellar medium (ISM), multiwavelength 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, that is, 2, 4, and 17 arcsec corresponding to a linear size of 144, 288, and 1.2 kpc, respectively. Our results indicate an asymmetry in the physical conditions along the galaxy's disc, that is, 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, and 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.
Molecular Line Ratio Diagnostics Along the Radial Cut and Dusty Ultraviolet-Bright Clumps in a Spiral Galaxy Ngc 0628
(Oxford Univ Press, 2020) Topal, Selcuk
Molecular emission lines are essential tools to shed light on many questions regarding star fonriation in galaxies. Multiple molecular lines are particularly useful to probe different phases of star-forming molecular clouds. In this study. we investigate the physical properties of giant molecular clouds (GMCs) using multiple lines of CO, 1.e. CO(1-0, 2-1. 3--2) and 13C0(1-0), obtained at selected 20 positions in the disc of NGC 0628. A total of 11 positions were selected over the radial cut, includinn the centre, and remaining 9 positions were selected :across the southern and northern arms of the galaxy. A total of 13 out of 20 positions are brighter at 24 um and ultraviolet (UV) emission and hosting significantly more H tl regions compared to the rest of the positions indicating opposite characteristics. Our line ratio 'analysis shows that the gas gets warmer and thinner as a function of radius from the galaxy centre up to 1.7 kpc. and then the ratios start to fluctuate. Our empincal and model results suggest that the UV-bright positions have colder and thinner CO gas with higher hydrogen and CO column densities. However, the UV-dim positions have relatively warmer CO gas with lower densities bathed in GMCs surrounded by less number of Hn regions. Analysis of multiwavelength infrared and UV data indicates that the UV-bright positions have higher star formation efficiency than that of the LIV-dim positions.
Molecular Line Ratio Diagnostics and Gas Kinematics in the Agn Host Seyfert Galaxy Ngc 5033
(Oxford Univ Press, 2021) Topal, Selcuk
Multiple molecular lines are useful for studying the physical properties of multiphase star-forming gas in different types of galaxies. We probe the molecular gas throughout the disc of the spiral galaxy NGC 5033, hosting an active galactic nucleus (AGN), using multiple low-J CO lines [(CO)-C-12(1-0, 2-1, 3-2 and (CO)-C-13(1-0, 2-1)] and dense gas tracers [HCN(1-0) and HCO+(1-0)]. First, we determine the ratios of the integrated intensity maps and the ratio of intensities in position velocity diagrams. Secondly, we obtain the ratios of CO lines and high-density tracers at the centre; and thirdly, we model these line ratios using a radiative transfer code. Line ratio diagnostics reveal that the south of the gaseous disc contains cooler gas than the northern part, and the centre hosts warmer and less tenuous gas with a similar dense gas fraction compared to most galaxies of similar type. Our model results mostly agree with the empirical ones in the sense that the central region of NGC 5033 harbours warmer gas than that in the centres of normal spirals and lenticulars without showing AGN activity. Finally, the beam-averaged total molecular gas mass and gas surface density along the galaxy's major axis show a radial gradient, i.e. increasing from the outskirts up to the central region of size 1 kpc where there is a depression in both gas mass and surface density.
Multiple-Line Study of Molecular Gas in Spiral Galaxy Ngc 2903
(Tubitak Scientific & Technological Research Council Turkey, 2018) Topal, Selcuk
Multiple molecular lines with radiative transfer modeling are a powerful tool to probe the physics of star-forming gas in galaxies. We investigate the gas properties in the center of spiral galaxy NGC 2903 using low- J CO lines, i.e. (CO)-C-12(1-0), (CO)-C-12(2-1), (CO)-C-12(3-2), (CO)-C-13(1-0), and HCN(1-0). We apply a nonlocal thermodynamic equilibrium radiative transfer code to derive beam-averaged molecular gas properties. We use two methods (i.e. chi(2) minimization and likelihood) to define the best model representing the observed line ratios best. The line ratio diagnostics suggest that CO gas in the center of NGC 2903 is thinner and the dense gas fraction is similar compared to that of spirals, starbursts, and early-type galaxies (ETGs), while the gas in the center of the galaxy is warmer than that of ETGs and colder than that of starbursts. Based on the best-fitting model results, we find that the beam-averaged gas kinetic temperature is T-K = 20 K, H-2 volume number density is log(n (H-2)) = 4.2 cm(-3), and CO column number density is log( N (CO)) = 19.0 cm(-2) in the center of NGC 2903. Both methods, i.e. the line ratio diagnostics and modeling, indicate an ISM in the center of NGC 2903 having intermediate temperature and star formation activity (also supported by star formation rates), thinner CO gas with similar dense gas fraction, and higher H-2 volume number density compared to that of spirals, ETGs, and starbursts.