Systematic variation of the CO / CO ratio as a function of star-formation rate surface density
نویسنده
چکیده
We show that the CO/CO intensity ratio in nearby galaxies varies systematically as a function of the star formation rate surface density (ΣSFR) and gas surface density. The same effect is observed in different transitions, and in the CO/CO ratio, while the CO/CO ratio appears to remain constant as a function of ΣSFR. We discuss the cause of these variations, considering both changes in the physical state of the gas, and chemical changes that lead to abundance variations. We used the observed correlations with CO to suggest that abundance variations are unlikely to be causing the systematic trend observed with ΣSFR, and thus that the mean gas temperature and/or velocity dispersion are systematically higher in higher starformation rate surface density regions. We present the best fitting relations between ΣSFR and the CO/CO and CO/CO ratios, and discuss how this effect can help us predict CO isotope emission from galaxies across the known universe.
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