Properties of Low Surface Brightness Galaxies and Normal Spirals in the Near-Infrared

Abstract

We present results for J and K-s near-IR imaging data on a large sample of 88 galaxies drawn from the catalog of Impey et al. The galaxies span a wide range in optical and IR surface brightness and morphology ( although they were drawn from a catalog constructed to identify low surface brightness galaxies [LSBGs]). They were also selected to include very low and high H I mass galaxies in order to ensure that they span a wide range of evolutionary states. The near-IR data unveil many features of LSBGs not seen before in the optical. First, a high fraction of the observed LSBGs are very luminous in the near-IR, indicating that they have a well-developed old stellar population and that older LSBGs are more frequent in the universe than data from optical bands suggested. Second, the near-IR morphologies are often quite different than those seen in the optical. Many diffuse LSBGs that are apparently bulgeless when observed in blue bands instead exhibit nuclei in J and K-s bands. Third, we find significant trends between the near-IR morphologies of the galaxies and their ratio of H I mass to near-IR luminosity. Fourth, we find no trend in disk surface brightness with absolute magnitude but significant correlations when the bulge surface brightness is used. Finally, we find that the formation of a bulge requires a galaxy to have a total baryonic mass above similar to10(10) M-.. A wide variety of other correlations are explored for the sample. We consider correlations among morphologies, surface brightnesses, near-IR colors, absolute magnitudes, and H I masses. In addition, using previous results by Bell & de Jong, we convert the galaxies near-IR luminosities to stellar masses on the basis of color-dependent stellar mass-to-light ratios. This allows us to consider correlations among more fundamental physical quantities, such as the H I mass, the stellar mass, the total baryonic mass, the gas mass fraction, the mass surface density, and the metallicity (via the highly metal sensitive color index J-K-s). We find that the strongest of our correlations are with the ratio of H I mass to total baryonic mass, M-HI/M-baryonic, which tracks the evolutionary state of the galaxies as they convert gas into stars and which ranges from 0.05 up to nearly 1 for the galaxies in our sample. We find strong systematic trends in how the metallicity-sensitive J-K-s color becomes redder with decreasing M-HI/M-baryonic, as would be expected for closed-box models of chemical enrichment. However, the increased scatter with increasing gas mass fraction and decreasing galaxy mass suggests that gas infall is increasingly significant in the gas-rich lower mass systems. We argue that the overall range in J-K-s color argues for at least a factor of 20 change in the mean stellar metallicity across the mass range spanned by our sample. We also see strong trends between M-HI/M-baryonic and central surface density, suggesting that increased star formation efficiency with increasing gas surface density strongly drives the conversion of gas into stars.