B. D. Simmons, C. Lintott, K. Schawinski, E. C. Moran, A. Han, S. Kaviraj, K. L. Masters, C. M. Urry, K. W. Willett, S. P. Bamford, R. C. Nichol
The growth of supermassive black holes appears to be driven by both galaxy mergers and `secular' processes that occur in their absence. In order to quantify the effects of secular evolution on black hole growth, we require a sample of active galactic nuclei (AGN) in galaxies that have formed without significant mergers, a population that heretofore has been difficult to locate. Here we present an initial sample of 13 AGN in massive (M_* \gtrsim 1e10 M_sun) bulgeless galaxies -- which lack the classical bulges believed inevitably to result from mergers -- selected from the Sloan Digital Sky Survey using visual classifications from Galaxy Zoo. Parametric morphological fitting confirms the host galaxies lack classical bulges; any contributions from pseudobulges are very small (typically < 5%). This is the largest such sample yet assembled. We compute black hole masses for the two broad-line objects in the sample (4.2e6 and 1.2e7 M_sun) and place lower limits on black hole masses for the remaining sample (typically M_BH \gtrsim 1e6 M_sun), showing that significant black hole growth must be possible in the absence of mergers. The black hole masses are systematically higher than expected from established bulge-black hole relations. However, if the mean Eddington ratio of the systems with measured black hole masses (L/L_Edd \approx 0.065) is typical, 10 of 13 sources are consistent with the correlation between black hole mass and total stellar mass. That pure disk galaxies and their central black holes may be consistent with a relation derived from elliptical and bulge-dominated galaxies with very different formation histories implies the details of stellar galaxy evolution and dynamics may not be fundamental to the co-evolution of galaxies and black holes.
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http://arxiv.org/abs/1207.4190
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