Properties of Molecular Gas in Massive Low Surface Brightness Galaxies,   Including New 12CO Observations of Three Malin 1 `Cousins'
  To date, the only low surface brightness (LSB) galaxies which have been detected in CO are the Massive LSB (MLSB) galaxies. In 2003, O'Neil, Schinnerer, & Hofner hypothesized that is the prominent bulge component in MLSB galaxies, not present in less massive low surface brightness galaxies, which gives rise to the detectable quantities of CO gas. To test this hypothesis, we have used the IRAM 30m telescope to obtain three new, deep CO J(1-0) and J(2-1) observations of MLSB galaxies. Two of the three galaxies observed were detected in CO - one in the J(1-0) line and the other in both the J(1-0) and J(2-1) lines, bringing the total number of MLSB galaxies with CO detections to 5, out of a total of 9 MLSB galaxies observed at CO to date. The third object had no detection to 2 mK at CO J(1-0). Comparing all MLSB galaxy CO results with surveys of high surface brightness galaxies, we find the MLSB galaxies' MH2 and MH2/MHI values fall within the ranges typically found for high surface brightness objects, albeit at the low end of the distribution, with the two MLSB galaxies detected at CO in this survey having the highest MH2/MHI values yet measured for any LSB system, by factors of 2-3. 
K. O'Neil & E. Schinnerer