Emission and Absorption Properties of Low-Mass Type 2 Active Galaxies
  with XMM-Newton
  We present XMM-Newton observations of four low-redshift Seyfert galaxies
selected to have low host luminosities (M_g>-20 mag) and small stellar velocity
dispersions (sigma_star<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 <10^6 M_sun. Three out
of four objects were detected with >3sigma 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
Gamma=1.1-1.8. Relative to [OIII], 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 [OIII] emission line luminosities are correlated with the
unabsorbed X-ray luminosity. The results are consistent with moderate
(N_H~10^22 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 [OIII] luminosities, the type 2 object has an
X-ray/[OIII] 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~10^40-10^41 erg/s.
