Dwarf galaxies with optical signatures of active massive black holes

Amy E. Reines, Jenny E. Greene, Marla Geha

Research output: Contribution to journalArticlepeer-review

222 Scopus citations

Abstract

We present a sample of 151 dwarf galaxies (108.5 ≲ M z.ast; ≲ 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.

Original languageEnglish (US)
Article number116
JournalAstrophysical Journal
Volume775
Issue number2
DOIs
StatePublished - Oct 1 2013

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • galaxies: Seyfert
  • galaxies: active
  • galaxies: dwarf
  • galaxies: nuclei

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