First Detection of CO in a Low Surface Brightness Galaxy

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Abstract
We report on the first attempts at searching for CO in red low surface brightness galaxies, and the first detection of molecular gas in a low surface brightness [μB(0)obs > 23 mag arcsec-2] galaxy. Using the IRAM 30 m telescope, CO (1-0) and CO (2-1) lines were searched for in four galaxies—P06-1, P05-5, C05-3, and C04-2. In three of the galaxies no CO was detected, to TMB ~ 1.8 mK (at the 3 σ level). In the fourth galaxy, P06-1, both lines were detected. Comparing our findings with previous studies shows P06-1 to have a molecular-to-atomic mass ratio considerably lower than is predicted using theoretical models based on high surface brightness galaxy studies. This indicates the N(H2)/ T(CO)dv conversion factor for low surface brightness galaxies may currently be consistently underestimated by a factor of 3-20.
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