The AGN and gas disc in the low surface brightness galaxy PGC 045080

Abstract

We present radio observations and optical spectroscopy of the giant low surface brightness (LSB) galaxy PGC045080 (or 1300+0144). PGC045080 is a moderately distant galaxy having a highly inclined optical disc and massive HI gas content. Radio continuum observations of the galaxy were carried out at 320, 610MHz and 1.4GHz. Continuum emission was detected and mapped in the galaxy. The emission appears extended over the inner disc at all three frequencies. At 1.4GHz and 610MHz it appears to have two distinct lobes. We also did optical spectroscopy of the galaxy nucleus; the spectrum did not show any strong emission lines associated with active galactic nucleus (AGN) activity but the presence of a weak AGN cannot be ruled out. Furthermore, comparison of the Hα flux and radio continuum at 1.4GHz suggests that a significant fraction of the emission is non-thermal in nature. Hence we conclude that a weak or hidden AGN may be present in PGC045080. The extended radio emission represents lobes/jets from the AGN. These observations show that although LSB galaxies are metal poor and have very little star formation, their centres can host significant AGN activity. We also mapped the HI gas disc and velocity field in PGC045080. The HI disc extends well beyond the optical disc and appears warped. In the HI intensity maps, the disc appears distinctly lopsided. The velocity field is disturbed on the lopsided side of the disc but is fairly uniform in the other half. We derived the HI rotation curve for the galaxy from the velocity field. The rotation curve has a flat rotation speed of ~190kms-1.