The multitude of unresolved continuum sources at 1.6 microns in Hubble Space Telescope images of Seyfert galaxies

A. C. Quillen, Colleen McDonald, A. Alonso-Herrero, Ariane Lee, Shanna Shaked, M. J. Rieke, G. H. Rieke

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


We examine 112 Seyfert galaxies observed by the Hubble Space Telescope at 1.6 μm. We find that ∼ 50% of the Seyfert 2.0 galaxies which are part of the Revised Shapely-Ames (RSA) Catalog or the CfA redshift sample contain unresolved continuum sources at 1.6 μm. All but a couple of the Seyfert 1.0-1.9 galaxies display unresolved continuum sources. The unresolved sources have fluxes of order 1 mJy, near infrared luminosities of order 1041 ergs s-1, and absolute magnitudes MH ∼ -16. Comparison non-Seyfert galaxies from the RSA Catalog display significantly fewer (∼20%), somewhat lower luminosity nuclear sources, which could be due to compact star clusters. We find that the luminosities of the unresolved Seyfert 1.0-1.9 sources at 1.6 μm are correlated with [O III] λ15007 and hard X-ray luminosities, implying that these sources are nonstellar. Assuming a spectral energy distribution similar to that of a Seyfert 2 galaxy, we estimate that a few percent of local spiral galaxies contain black holes emitting as Seyferts at a moderate fraction, ∼10-1-10-4, of their Eddington luminosities. We find no strong correlation between 1.6 μm fluxes and hard X-ray or [O III] λ5007 fluxes for the pure Seyfert 2.0 galaxies. These galaxies also tend to have lower 1.6 μm luminosities compared to the Seyfert 1.0-1.9 galaxies of similar [O III] luminosity. Either large extinctions (AV ∼ 20-40) are present toward their continuumemitting regions or some fraction of the unresolved sources at 1.6 μ are compact star clusters. With increasing Seyfert type the fraction of unresolved sources detected at 1.6 μm and the ratio of 1.6 μm to [O III] fluxes tend to decrease. These trends are consistent with the unification model for Seyfert 1 and 2 galaxies.

Original languageEnglish (US)
Pages (from-to)129-139
Number of pages11
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - Jan 20 2001


  • Galaxies: Seyfert
  • Galaxies: nuclei
  • Galaxies: spiral

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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