Issue |
A&A
Volume 451, Number 1, May III 2006
|
|
---|---|---|
Page(s) | 35 - 44 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20053799 | |
Published online | 25 April 2006 |
The Chandra view of the 3C/FR I sample of low luminosity radio-galaxies
1
Dipartimento di Fisica Generale, Universitá di Torino, via P. Giuria 1, 10125 Torino, Italy e-mail: balmaverde@ph.unito.it
2
INAF – Osservatorio Astronomico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy e-mail: capetti@to.astro.it
3
INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, via Gobetti 101, 40129 Bologna, Italy e-mail: grandi@bo.iasf.cnr.it
Received:
8
July
2005
Accepted:
19
December
2005
We present results from Chandra observations of the 3C/FR I sample of low luminosity radio-galaxies. We detected a power-law nuclear component in 12 objects out of the 18 with
available data. In 4 galaxies we detected nuclear X-ray
absorption at a level of
1022 cm-2.
X-ray absorbed sources are associated with the presence
of highly inclined dusty disks (or dust filaments projected
onto the nuclei) seen in the HST images. This suggests the existence of a flattened X-ray absorber,
but of much lower optical depth than in classical obscuring tori. We thus have an unobstructed view toward most FR I nuclei, while absorption plays only a marginal role
in the remaining objects.
Three pieces of evidence support a jet origin for the X-ray cores: i) the presence of strong correlations between the nuclear luminosities in the radio, optical, and X-ray bands,
extending over 4 orders of magnitude and having a much smaller dispersion
(~0.3 dex) when compared to similar trends found for other classes of AGNs, all of which points to a common origin for the emission in the three bands; ii) the close similarity of the
broad-band spectral indices with the sub-class of BL Lac objects sharing
the same range of extended radio-luminosity, in accord with the
FR I/BL Lacs unified model; iii) the presence of a common luminosity evolution of spectral indices in both FR I and BL Lacs. The low luminosities of the X-ray nuclei, regardless of their
origin, strengthens the interpretation of low efficiency accretion
in low luminosity radio-galaxies.
Key words: galaxies: active / galaxies: BL Lacertae objects: general / galaxies: nuclei / galaxies: jets
© ESO, 2006
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