EMISSION AND ABSORPTION PROPERTIES OF LOW-MASS TYPE 2 ACTIVE GALAXIES WITH XMM-NEWTON
- Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, Irvine, CA 92619-4575 (United States)
- Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States)
We present XMM-Newton observations of four low-redshift Seyfert galaxies selected to have low host luminosities (M{sub g} > - 20 mag) and small stellar velocity dispersions (sigma{sub *} <45 km s{sup -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 approx<10{sup 6} M{sub sun}. Three out of four objects were detected with >3sigma significance in approx25 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 [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 {sub H} approx 10{sup 22} cm{sup -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 {sub bol} approx10{sup 40}-10{sup 41} erg s{sup -1}.
- OSTI ID:
- 21378320
- Journal Information:
- Astrophysical Journal, Vol. 705, Issue 2; Other Information: DOI: 10.1088/0004-637X/705/2/1196; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COSMOLOGY AND ASTRONOMY
ABSORPTION
BLACK HOLES
COMPARATIVE EVALUATIONS
DISPERSIONS
GALAXY NUCLEI
LUMINOSITY
MASS
PHOTONS
RED SHIFT
SEYFERT GALAXIES
SIGNAL-TO-NOISE RATIO
SPECTRA
UNIFIED MODEL
X-RAY GALAXIES
BOSONS
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
DIMENSIONLESS NUMBERS
ELEMENTARY PARTICLES
EVALUATION
GALAXIES
MASSLESS PARTICLES
MATHEMATICAL MODELS
NUCLEAR MODELS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
SORPTION