(CO)-C-12(3-2) emission in spiral galaxies: Warm molecular gas in action?

Abstract

Using the APEX submillimeter telescope we have investigated the (CO)-C-12(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 similar to 90 and similar to 73 km s(-1) and integrated intensities of 1.20 and 0.76 K km s(-1), respectively. For the nondetections, the estimated upper limit for the integrated intensity is similar to 0.54 K km s. With these figures we estimate the H-2 masses as well as the atomic- to- molecular mass ratios. Although all the galaxies are barred, we observe (CO)-C-12( 3-2) emission only for galaxies with prominent bars. We speculate that bars could dynamically favor the (CO)-C-12(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 (CO)-C-12(3-2), especially in LSBs.