CO detection and millimeter continuum emission from low surface brightness galaxies

Abstract

We present BIMA and IRAM CO (1-0) observations of seven low surface brightness (LSB) galaxies, including three large spiral galaxies with faint disks but prominent bulges and four relatively small LSB galaxies with irregular disks. The giant LSB galaxies are UGC 5709, UGC 6614, and F568-6 (Malin 2). The smaller LSB galaxies are NGC 5585, UGC 4115, UGC 5209, and F583-1. The galaxies were selected based on their relatively high metallicity and apparent signs of star formation in their disks. The BIMA maps suggested the presence of molecular gas in two of the giant LSB galaxies: F568-6 and UGC 6614. Using the 30 m IRAM telescope, we detected CO (1-0) emission in the disks of both galaxies and in the nucleus of F568-6. The molecular gas in these galaxies is clearly offset from the nucleus and definitely associated with the LSB disk. In addition, we detected a millimeter continuum source in the center of UGC 6614. When compared with Very Large Array (VLA) 1.5 GHz observations of the galaxy, the emission was found to have a flat spectrum, indicating that the millimeter continuum emission is most likely due to an active galactic nucleus (AGN) in the galaxy. Our results show that giant LSB spiral galaxies may contain significant quantities of molecular gas in their disks and also harbor radio-bright AGNs in their centers.