2023/07/26 by Hiroyuki Kaneko, Kaneko, Hiroyuki, Tomoka Tosaki +5
Chemistry · Decision Sciences · #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Scientific Measurement and Uncertainty Evaluation #Spectroscopy and Chemometric Analyses #Spectroscopy and Laser Applications
paper · pdf · doi:10.48550/arxiv.2307.14092
openalex publication_date 2023/07/26 · openalex created_date 2023/07/28 · openalex updated_date 2026/07/28
We present position-position-velocity (PPV) cubes of the physical and chemical properties of the molecular medium in the central 1.2 kpc region of the active galaxy NGC 613 at a PPV resolution of 0.′′8×0.′′8×10 km s-1 (0.′′8 = ∼68 pc). We used eight molecular lines obtained with ALMA. Non-LTE calculation with hierarchical Bayesian inference was used to construct PPV cubes of the gas kinetic temperature (Tkin), molecular hydrogen volume density (nH2), column densities (NH2), and fractional abundances of four molecules (12C18O, HCN, HCO+, and CS). The derived nH2, NH2, and Tkin ranged 103.21-3.85 cm-3, 1020.8-22.1 cm-2, and 102.33-2.64 K, respectively. Our first application of the non-LTE method with the hierarchical Bayesian inference to external galaxies yielded compatible results compared with the previous studies of this galaxy, demonstrating the efficacy of this method for application to other galaxies. We examined the correlation between gas surface density ΣH2 (converted from NH2) and the star formation rate ΣSFR obtained from the 110 GHz continuum flux map and found two distinct sequences in the ΣH2-ΣSFR diagram; the southwestern subregion of the star-forming ring exhibited a ∼0.5 dex higher star formation efficiency (SFE; ΣSFR/ΣH2) than the eastern subregion. However, they exhibited no systematic difference in nH2, which is often argued as a driver of SFE variation. We suggest that the deficiency of molecular gas in the southwestern subregion, where no significant gas supply is evident along the offset ridges in the bar, is responsible for the elevated SFE.