The soft X-ray/NLR connection: a single photoionized medium?

¹ XMM-Newton Science Operations Center, European Space Astronomy Center, ESA, Apartado 50727, 28080 Madrid, Spain e-mail: Stefano.Bianchi@sciops.esa.int
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
³ INAF – Istituto di Radioastronomia, via P. Gobetti 101, 40129 Bologna, Italy

Received: 23 August 2005
Accepted: 29 October 2005

Abstract

We present a sample of 8 nearby Seyfert 2 galaxies observed by HST and Chandra. All of the sources present soft X-ray emission which is coincident in extension and overall morphology with the [O iii] emission. The spectral analysis reveals that the soft X-ray emission of all the objects is likely to be dominated by a photoionized gas. This is strongly supported by the 190 ks combined XMM-Newton/RGS spectrum of Mrk 3, which different diagnostic tools confirm as being produced in a gas in photoionization equilibrium with an important contribution from resonant scattering. We tested with the code cloudy a simple scenario where the same gas photoionized by the nuclear continuum produces both the soft X-ray and the [O iii] emission. Solutions satisfying the observed ratio between the two components exist, and require the density to decrease with radius roughly like r^-2, similarly to what often found for the Narrow Line Region.