paper

Internal structure of molecular gas in a main sequence galaxy with a UV clump at z = 1.45

arXiv:2101.08396 · doi:10.3847/1538-4357/abdd1f

Abstract

We present results of sub-arcsec ALMA observations of CO(2-1) and CO(5-4) toward a massive main sequence galaxy at z = 1.45 in the SXDS/UDS field, aiming at examining the internal distribution and properties of molecular gas in the galaxy. Our target galaxy consists of the bulge and disk, and has a UV clump in the HST images. The CO emission lines are clearly detected and the CO(5-4)/CO(2-1) flux ratio (R_52) is ~1, similar to that of the Milky Way. Assuming a metallicity dependent CO-toH_2 conversion factor and a CO(2-1)/CO(1-0) flux ratio of 2 (the Milky Way value), the molecular gas mass and the gas mass fraction (f_gas = molecular gas mass / (molecular gas mass + stellar mass)) are estimated to be ~1.5x10^11 M_Sun and ~0.55, respectively. We find that R_52 peak coincides with the position of the UV clump and its value is approximately two times higher than the galactic average. This result implies high gas density and/or high temperature in the UV clump, which qualitatively agrees with a numerical simulation of a clumpy galaxy. The CO(2-1) distribution is well represented by a rotating disk model and its half-light radius is ~2.3 kpc. Compared to the stellar distribution, the molecular gas is more concentrated in the central region of the galaxy. We also find that f_gas decreases from ~0.6 at the galactic center to ~0.2 at 3xhalf-light radius, indicating that the molecular gas is distributed in more central region of the galaxy than stars and seems to associate with the bulge rather than the stellar disk.

14 pages, 10 figures, 4 tables; Accepted for publication in ApJ

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