CO Emissions from Optically Selected Galaxies at z∼0.1–0.2: Tight Anti-Correlation Between Molecular Gas Fraction and 4000 Angstrom Break Strength


Paper:	CO Emissions from Optically Selected Galaxies at z∼0.1–0.2: Tight Anti-Correlation Between Molecular Gas Fraction and 4000 Angstrom Break Strength
Volume:	499, Revolution in Astronomy with ALMA: The Third Year
Page:	157
Authors:	Morokuma-Matsui, K.; Baba, J.; Sorai, K.; Kuno, N.
Abstract:	We performed ¹²CO(J=1–0) (hereafter, CO) observations towards 12 normal star-forming galaxies with M_⋆=10^10.6–10^11.3 M_☉ at z=0.1–0.2 with the 45-m telescope at the Nobeyama Radio Observatory (NRO). The samples are selected with D_n(4000) that is a measure of the 4000 Angstrom break strength, instead of commonly used far-infrared (FIR) flux. We detect the CO emissions from 8 galaxies with signal-to-noise ratio (S/N) larger than 3, demonstrating the effectiveness of the D_n(4000)-based sample selection. We find a tight anti-correlation between D_n(4000) and molecular gas fraction (f_mol) using literature data of nearby galaxies in which the galaxies with more fuel for star formation have younger stellar populations. CO-detected galaxies at z∼0.1–0.2 also follow the same relation of nearby galaxies, implying 1) the galaxies evolve along this D_n(4000)–f_mol relation, and 2) D_n(4000) seems to be used as a proxy for f_mol which requires many time-consuming observations¹.