The galactic spin of AGN galaxies

Abstract

Using an extensive sample of galaxies selected from the Sloan Digital Sky Survey Data Release 5, we compare the angular momentum distribution of active galactic nucleus (AGN) with non-AGN hosting late-type galaxies. To this end we characterize galactic spin through the dimensionless angular momentum parameter $λ$, which we estimate approximately through simple dynamical considerations. Using a volume limited sample, we find a considerable difference when comparing the empirical distributions of $λ$ for AGNs and non-AGN galaxies, the AGNs showing typically low $λ$ values and associated dispersions, while non-AGNs present higher $λ$ values and a broader distribution. A more striking difference is found when looking at $λ$ distributions in thin $M_{r}$ cuts, while the spin of non-AGN galaxies presents an anti-correlation with $M_{r}$, with bright (massive) galaxies having low spins, AGN host galaxies present uniform values of $λ$ at all magnitudes, a behavior probably imposed by the fact that most late-type AGN galaxies present a narrow range in color, with a typical constant $λ$ value. We also find that the fraction of AGN hosting galaxies in our sample strongly depends on galactic spin, increasing dramatically for decreasing $λ$. For AGN host galaxies we compute the mass of their supermassive black holes and find that this value tends to be higher for low spin galaxies, even at fixed luminosity, a result that could account, to a certain extent, for the spread on the luminosity black-hole mass relation.

6 pages, 4 figures, published in ApJ Letters, final version