CI emission in Ultra Luminous Infrared Galaxies as a molecular gas mass tracer
Abstract
We present new sensitive wide-band measurements of the fine structure line 3P1 -> 3P0 (J=1-0, 492GHz) of neutral atomic carbon (CI) in the two typical Ultra Luminous Infrared Galaxies NGC6240 and Arp220. We then use them along with several other CI measurements in similar objects found in the literature to estimate their global molecular gas content under the assumption of a full CI-H2 concomitance. We find excellent agreement between the H2 gas mass estimated with this method and the standard methods using 12CO. This may provide a new way to measure H2 gas mass in galaxies, and one which may be very valuable in ULIRGs since in such systems the bright 12CO emission is known to systematically overestimate the gas mass while their 13CO emission is usually very weak. At redshifts z>=1 the CI J=1-0 line shifts to much more favorable atmospheric windows and can become a viable alternative tracer of the H2 gas fueling starburst events in the distant Universe.
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