Soft X‐Ray Properties of Seyfert Galaxies in the ROSAT All‐Sky Survey

Abstract

We present the results of ROSAT All-Sky Survey observations of Seyfert and IR luminous galaxies from the extended 12 μm galaxy sample and the optically selected CfA sample. Detections are available for 80% (44/55) of the Seyfert 1's and 34% (23/67) of the Seyfert 2's in the 12 μm sample, and for 76% (26/34) of the Seyfert 1's and 38% (6/16) of the Seyfert 2's in the CfA Sample. Roughly half of the Seyfert galaxies (mostly Seyfert 1's) have been fitted to an absorbed power-law model, yielding an average photon index of Γ = 2.26 ± 0.11 for 43 Seyfert 1's and Γ = 2.45 ± 0.18 for 10 Seyfert 2's, with both types having a median value of 2.3. The soft X-ray luminosity corelates with the 12 μm luminosity, with Seyfert 1's, having relatively more soft X-ray emission than Seyfert 2's of similar mid-IR luminosities by factor of 1.6 ± 0.3. Several physical interpretaions of these results are discused, including the standard unified model for Seyfert galaxies. Infrared luminous non-Seyferts are shown to have similar disributions of soft X-ray luminosity and X-ray-to-IR slope as Seyfert 2's suggesting that some of them may harbor obscured active nuclei (as has already ben shown to be true for several objects) and/or that the soft X-rays from some Seyfert 2's may be nonnuclear. A soft X-ray luminosity function (XLF) is calculated for the 12 μm sample, which is described well by a single power law with a slope of −1.75. The normalization of this XLF agrees well with that of a hard X-ray selected sample. Several of our results, related to the XLF and the X-ray-to-IR relation, are shown to be consistent with the hard x-ray observations of the 12 μm sample by barcons et al.