Dwarf Galaxies with Optical Signatures of Active Massive Black Holes
Abstract
We present a sample of 151 dwarf galaxies (108.5 <~ M sstarf <~ 109.5 M ⊙) that exhibit optical spectroscopic signatures of accreting massive black holes (BHs), increasing the number of known active galaxies in this stellar-mass range by more than an order of magnitude. Utilizing data from the Sloan Digital Sky Survey Data Release 8 and stellar masses from the NASA-Sloan Atlas, we have systematically searched for active BHs in ~25,000 emission-line galaxies with stellar masses comparable to the Magellanic Clouds and redshifts z < 0.055. Using the narrow-line [O III]/Hβ versus [N II]/Hα diagnostic diagram, we find photoionization signatures of BH accretion in 136 galaxies, a small fraction of which also exhibit broad Hα emission. For these broad-line active galactic nucleus (AGN) candidates, we estimate BH masses using standard virial techniques and find a range of 105 <~ M BH <~ 106 M ⊙ and a median of M BH ~ 2 × 105 M ⊙. We also detect broad Hα in 15 galaxies that have narrow-line ratios consistent with star-forming galaxies. Follow-up observations are required to determine if these are true type 1 AGN or if the broad Hα is from stellar processes. The median absolute magnitude of the host galaxies in our active sample is Mg = -18.1 mag, which is ~1-2 mag fainter than previous samples of AGN hosts with low-mass BHs. This work constrains the smallest galaxies that can form a massive BH, with implications for BH feedback in low-mass galaxies and the origin of the first supermassive BH seeds.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2013
- DOI:
- 10.1088/0004-637X/775/2/116
- arXiv:
- arXiv:1308.0328
- Bibcode:
- 2013ApJ...775..116R
- Keywords:
-
- galaxies: active;
- galaxies: dwarf;
- galaxies: nuclei;
- galaxies: Seyfert;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 26 pages, 15 figures, 6 tables. Accepted for publication in The Astrophysical Journal