Evolution of Gas and Stars in Galaxies over the last 12 billion years
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Nick Scoville
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At present epochs, stars dominate the baryonic mass of Galaxies, but at early ages the gas which fuels both star formation and AGN accretion must have been dominant. We have used ALMA archive data in the COSMOS 2-deg^2 field to measure the gas masses for samples of 700 and 10,000 galaxies at redshift 0.1 to 6, corresponding to a span of 12 Gyr. The range of measured gas masses is 10^9 - few x 10^11 solar masses -- the latter being ~ 100x that in the Milky Way. The dependence of gas mass on cosmic age, stellar mass of the galaxy and starburst activity is characterized and used to infer gas accretion rates and evolutionary paths for the galaxies. The dependence of the galaxy evolution on gas content versus efficiency for forming stars (per unit mass of gas) are separated. Earlier than cosmic age 5 Gyr (z = 1.2), the interstellar gas was the dominant baryonic mass component of galaxies. 

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