Astronomy and Astrophysics, volume 530A, 147-147 (2011/6-1)
Megamaser detection and nuclear obscuration in Seyfert galaxies.
RAMOLLA M., HAAS M., BENNERT V.N. and CHINI R.
Abstract (from CDS):
We revisit the relation between H2O maser detection rate and nuclear obscuration for a sample of 114 Seyfert galaxies drawn from the CfA, 12µm, and IRAS F25/F60 catalogs. These sources have mid-infrared spectra from the Spitzer Space Telescope and we search for accompanying X-ray and [OIII]5007Å fluxes from the literature. We use the strength of the [OIV]25.9µm emission line as a tracer of the intrinsic AGN strength. After the normalization by [OIV], the observed X-ray flux provides information about X-ray absorption. The distribution of X-ray/[OIV] flux ratios is significantly different for masers and non-masers: The maser detected Seyfert-2s (Sy 1.8-2.0) populate a distinct X-ray/[OIV] range, which is, on average, about a factor of four lower than the range of Seyfert-2 non-masers and about a factor of ten lower than the range of Seyfert-1s (Sy 1.0-1.5). Non-masers are almost equally distributed over the entire X-ray/[OIV] range. This provides evidence that high nuclear obscuration plays a crucial role in determining the probability of maser detection. Furthermore, after normalization with [OIV], we find a similar but weaker trend for the distribution of the maser detection rate with the absorption of the 7µm dust continuum. This suggests that the obscuration of the 7µm continuum occurs on larger spatial scales than that of the X-rays. Hence, in the AGN unified model, at moderate inclinations away from edge-on, the 7µm dust absorption may occur without any proportionate X-ray absorption. The absorption of [OIII] appears unrelated to maser detections. The failure to detect masers in obscured AGN is most likely due to insufficient observational sensitivity.
galaxies: Seyfert - galaxies: nuclei - masers - X-rays: galaxies - infrared: galaxies
VizieR on-line data:
<Available at CDS (J/A+A/530/A147): table1.dat table3.dat refs.dat>
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