The growth of supermassive black holes appears to be driven by galaxy mergers, violent merger-free processes and/or ‘secular’ processes. In order to quantify the effects of secular evolution on black hole growth, we study a sample of active galactic nuclei (AGN) in galaxies with a calm formation history free of significant mergers, a population that heretofore has been difficult to locate. Here we present an initial sample of 13 AGN in massive (M* ≳ 1010 M⊙) 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 that the host galaxies lack classical bulges; any contributions from pseudo-bulges are very small (typically <5 per cent). We compute black hole masses for the two broad-line objects in the sample (4.2 × 106 and 1.2 × 107 M⊙) and place lower limits on black hole masses for the remaining sample (typically MBH ≳ 106 M⊙), showing that significant black hole growth must be possible in the absence of mergers or violent disc instabilities.
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/LEdd ≈ 0.065) is typical, 10 of 13 sources are consistent with the correlation between black hole mass and total stellar mass. That pure disc 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.
|Journal||Monthly Notices of the Royal Astronomical Society|
|Early online date||4 Jan 2013|
|Publication status||Published - 1 Mar 2013|
- galaxies: active
- galaxies: bulges
- galaxies: evolution
- galaxies: general
- galaxies: Seyfert
- galaxies: spiral