¹²CO(J=3→2) detections in bulges of low surface brightness galaxies with APEX

Abstract

Using the APEX sub-millimeter telescope we have detected for the first time the CO rotational transition ¹²CO(J=3→2) in two of five low surface brightness galaxies. For galaxies with positive detection, the emission is detected in their bulges, with measured gas velocity dispersion of about 80 km/s and observed main-beam brightness temperature T_{M B} ~ 10 mK. Using a standard CO to H₂ conversion factor, we are able to estimate molecular gas masses for LSBs with positive detections, and upper limits for those LSBs with negative detections. Assuming a higher gas temperature for the generation of the ¹²CO(J=3→2) line compared to that for the ¹²CO(J=1→0) one, results suggest that a warm molecular gas component is present in bulges, indicating a radiation field preventing the formation of large cooler amounts of molecular gas, compared to high surface brightness galaxies with higher metallicity and likely more dust.