0 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 30m telescope, CO(1-0) and CO(2-1) lines were searched for in four galaxies – P06-1, P05-5, C05-3, & C04-2. In three of the galaxies no CO was detected, to T M B ∼1.8mK (at the 3σ 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. 1 Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNSR (France), MPG (Germany) and IGN (Spain).