2008ApJ...677L..13G

Using the APEX submillimeter telescope we have investigated the ^ 12^CO(3-2) emission in five face-on nearby barred spiral galaxies, where three of them are high surface brightness galaxies (HSBs) lying at the Freeman limit, and two are low surface brightness galaxies (LSBs). We have positive detections for two of three HSB spirals and nondetections for the LSBs. For the galaxies with positive detection (NGC 0521 and PGC 070519), the emission is confined to their bulges, with velocity dispersions of ∼90 and ∼73 km/s and integrated intensities of 1.20 and 0.76 K km/s, respectively. For the nondetections, the estimated upper limit for the integrated intensity is ∼0.54 K km/s. With these figures we estimate the H₂ masses as well as the atomic-to-molecular mass ratios. Although all the galaxies are barred, we observe ¹²CO(3-2) emission only for galaxies with prominent bars. We speculate that bars could dynamically favor the ¹²CO(3-2) emission, as a second parameter after surface brightness. Therefore, secular evolution could play a major role in boosting collisional transitions of molecular gas, such as ¹²CO(3-2), especially in LSBs.