Volume 545, September 2012
|Number of page(s)||15|
|Published online||21 September 2012|
Extended soft X-ray emission in 3CR radio galaxies at z < 0.3: high excitation and broad line galaxies⋆
1 INAF – Osservatorio Astrofisico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy
2 INAF – IASF – Istituto di Astrofisica e Fisica cosmica di Bologna, via P. Gobetti 101, 40129 Bologna, Italy
3 INAF – Istituto di Radioastronomia di Bologna, via Gobetti 101, 40129 Bologna, Italy
4 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
5 Center for Astrophysical Sciences, Johns Hopkins University, 3400 N. Charles Street Baltimore, MD 21218, USA
6 Instituto de Astrofísica de Canarias, Calle vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
7 European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei Muenchen, Germany
8 Dept of Physics, Rochester Institute of Technology, 84 Lomb Memorial Dr., Rochester, NY 14623, USA
9 School of Mathematical and Physical Sciences, University of Sussex, Falmer, Brighton, BN2 9BH, UK
10 Carlson Center for Imaging Science, 84 Lomb Memorial Dr., Rochester, NY 14623, USA
11 Radcliffe Institute for Advanced Study, 10 Garden St. Cambridge, MA 02138, USA
12 Dipartimento di Astronomia, Universitá di Bologna, via Ranzani 1, 40127 Bologna, Italy
13 Harvard Smithsonian Center for Astrophysics, 60 Garden St. Cambridge, MA 02138, USA
Received: 8 May 2012
Accepted: 1 August 2012
We analyze Chandra observations of diffuse soft X-ray emission associated with a complete sample of 3CR radio galaxies at z < 0.3. We focus on the properties of the spectroscopic sub-classes of high excitation galaxies (HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or possibly extended) emission in about 40% of the sources; the fraction is even higher (8/10) when restricting the analysis to the objects with exposure times larger than 10 ks. In the 18 BLOs, extended emission is seen only in two objects; this lower detection rate can be ascribed to the presence of their bright X-ray nuclei that easily outshine any genuine diffuse emission. A very close correspondence between the soft X-ray and optical line morphology emerges. We also find that the ratio between [O III] and extended soft X-ray luminosity is confined within a factor of 2 around a median value of 5. Both results are similar to what is seen in Seyfert galaxies. We discuss different processes that could explain the soft X-ray emission and conclude that the photoionization of extended gas, coincident with the narrow line region, is the favored mechanism.
Key words: galaxies: active / X-rays: galaxies / ISM: jets and outflows
Appendix A is available in electronic form at http://www.aanda.org
© ESO, 2012
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