Studying the radio continuum from nuclear activity and star formation in giant low surface brightness galaxies

Abstract

We present a multifrequency radio continuum study of seven giant low surface brightness (GLSB) galaxies using the Giant Metrewave Radio Telescope (GMRT). GLSB galaxies are optically faint, dark-matter-dominated systems that are poorly evolved and have large H I gas discs. Our sample consists of GLSB galaxies that show signatures of nuclear activity in their optical spectra. We detect radio emission from the nuclei of all the seven galaxies. Five galaxies have nuclear spectral indices that range from 0.12 to −0.44 and appear to be core dominated; the two galaxies have a steeper spectrum. Two of the galaxies, UGC 2936 and UGC 4422, show significant radio emission from their discs. In our 610 MHz observations of UGC 6614, we detect radio lobes associated with the radio-loud active galactic nucleus (AGN). The lobes have a spectral index of −1.06 ± 0.12. The star formation rates estimated from the radio emission, for the entire sample range from 0.15 to 3.6 M⊙ yr−1. We compare the radio images with the near-ultraviolet (NUV) images from GALEX and near-infrared (NIR) images from 2MASS. The galaxies present a diversity of relative NUV, NIR and radio emission, supporting an episodic star formation scenario for these galaxies. Four galaxies are classified members of groups and one is classified as isolated. Our multiwavlength study of this sample suggests that the environment plays an important role in the evolution of these galaxies.