Emission and absorption properties of Low-mass type 2 active galaxies with XMM-newton

Carol E. Thornton, Aaron J. Barth, Luis C. Ho, Jenny E. Greene

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

We present XMM-Newton observations of four low-redshift Seyfert galaxies selected to have low host luminosities (Mg > - 20 mag) and small stellar velocity dispersions (σ* <45 km s -1), which are among the smallest stellar velocity dispersions found in any active galaxies. These galaxies show weak or no broad optical emission lines and have likely black hole masses ≲106 M . Three out of four objects were detected with >3σ significance in ∼ 25 ks exposures and two observations had high enough signal-to-noise ratios for rudimentary spectral analysis. We calculate hardness ratios (-0.43 to 0.01) for the three detected objects and use them to estimate photon indices in the range of Γ = 1.1-1.8. Relative to [O III], the type 2 objects are X-ray faint in comparison with Seyfert 1 galaxies, suggesting that the central engines are obscured. We estimate the intrinsic absorption of each object under the assumption that the [O III] emission line luminosities are correlated with the unabsorbed X-ray luminosity. The results are consistent with moderate (N H ∼ 1022 cm-2) absorption over the Galactic values in three of the four objects, which might explain the non-detection of broad-line emission in optical spectra. One object in our sample, SDSS J110912.40+612346.7, is a near identical type 2 counterpart of the late-type Seyfert 1 galaxy NGC 4395. While the two objects have very similar [O III] luminosities, the type 2 object has an X-ray/[O III] flux ratio nearly an order of magnitude lower than NGC 4395. The most plausible explanation for this difference is absorption of the primary X-ray continuum of the type 2 object, providing an indication that obscuration-based unified models of active galaxies can apply even at the lowest luminosities seen among Seyfert nuclei, down to L bol∼ 1040-1041 erg s-1.

Original languageEnglish (US)
Pages (from-to)1196-1205
Number of pages10
JournalAstrophysical Journal
Volume705
Issue number2
DOIs
StatePublished - 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Galaxies: Active
  • Galaxies: Nuclei
  • Galaxies: Seyfert
  • Galaxies: dwarf
  • X-rays: Galaxies

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