First Detection of CO in a Low Surface Brightness Galaxy

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 [μ B (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 T MB ~ 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 (H 2 )/ T (CO) dv conversion factor for low surface brightness galaxies may currently be consistently underestimated by a factor of 3-20.