VALES VI: ISM enrichment in star-forming galaxies up to z$\sim$0.2 using ${}^{12}$CO(1-0), ${}^{13}$CO(1-0) and C${}^{18}$O(1-0) line luminosity ratios

Abstract

We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations towards 27 low-redshift ($0.02<z<0.2$) star-forming galaxies taken from the Valparaíso ALMA/APEX Line Emission Survey (VALES). We perform stacking analyses of the ${}^{12}$CO($1-0$), ${}^{13}$CO($1-0$) and C${}^{18}$O($1-0$) emission lines to explore the $L^{\prime }$ (${}^{12}$CO($1-0$))/$L^{\prime }$(${}^{13}$CO($1-0$))) (hereafter $L^{\prime }$(${}^{12}$CO)/$L^{\prime }$(${}^{13}$CO)) and $L^{\prime }$(${}^{13}$CO($1-0$))/$L^{\prime }$(C${}^{18}$O($1-0$)) (hereafter $L^{\prime }$(${}^{13}$CO)/$L^{\prime }$(C${}^{18}$O) line luminosity ratio dependence as a function of different global galaxy parameters related to the star formation activity. The sample has far-IR luminosities $10^{10.1-11.9}$L${}_{\odot }$ and stellar masses of $10^{9.8-10.9}$M${}_{\odot }$ corresponding to typical star-forming and starburst galaxies at these redshifts. On average we find a $L^{\prime }$(${}^{12}$CO)/$L^{\prime }$(${}^{13}$CO) line luminosity ratio value of 16.1$\pm$2.5. Galaxies with evidences of possible merging activity tend to show higher $L^{\prime }$(${}^{12}$CO)/$L^{\prime }$(${}^{13}$CO) ratios by a factor of two, while variations of this order are also found in galaxy samples with higher star formation rates or star formation efficiencies. We also find an average $L^{\prime }$(${}^{13}$CO)/$L^{\prime }$(C${}^{18}$O) line luminosity ratio of 2.5$\pm$0.6, which is in good agreement with those previously reported for starburst galaxies. We find that galaxy samples with high $L_{\text{IR}}$, SFR and SFE show low $L^{\prime }$(${}^{13}$CO)/$L^{\prime }$(C${}^{18}$O) line luminosity ratios with high $L^{\prime }$(${}^{12}$CO)/$L^{\prime }$(${}^{13}$CO) line luminosity ratios, suggesting that these trends are produced by selective enrichment of massive stars in young starbursts.

16 pages, 10 figures to be published in MNRAS