2009ApJ...705.1196T -
Astrophys. J., 705, 1196-1205 (2009/November-2)
Emission and absorption properties of low-mass type 2 active galaxies with XMM-Newton.
THORNTON C.E., BARTH A.J., HO L.C. and GREENE J.E.
Abstract (from CDS):
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), 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 (NH∼ 1022/cm2) 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 Lbol∼1040-1041 erg/s.
Abstract Copyright:
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Journal keyword(s):
galaxies: active - galaxies: dwarf - galaxies: nuclei - galaxies: Seyfert - X-rays: galaxies
Simbad objects:
9
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