TY - JOUR
T1 - The vla survey of the chandra deep field-south. III. X-ray spectral properties of radio sources
AU - Tozzi, P.
AU - Mainieri, V.
AU - Rosati, P.
AU - Padovani, P.
AU - Kellermann, K. I.
AU - Fomalont, E.
AU - Miller, N.
AU - Shaver, P.
AU - Bergeron, J.
AU - Brandt, W. N.
AU - Brusa, M.
AU - Giacconi, R.
AU - Hasinger, G.
AU - Lehmer, B. D.
AU - Nonino, M.
AU - Norman, C.
AU - Silverman, J.
PY - 2009
Y1 - 2009
N2 - We discuss the X-ray properties of the radio sources detected in a deep 1.4 and 5 GHz VLA Radio survey of the Extended Chandra Deep Field-South (E-CDFS). Among the 266 radio sources detected, we find 89 sources (1/3 of the total) with X-ray counterparts in the catalog of the 1 Ms exposure of the central 0.08 deg2 or in the catalog of the 250 ks exposure of the 0.3 deg 2 E-CDFS field. For 76 (85%) of these sources, we have spectroscopic or photometric redshifts, and therefore we are able to derive their intrinsic properties from X-ray spectral analysis, namely intrinsic absorption and total X-ray luminosities. We find that the population of submillijansky radio sources with X-ray counterparts is composed of a mix of roughly 1/3 star-forming galaxies and 2/3 active galactic nuclei (AGNs). The distribution of intrinsic absorption among X-ray-detected radio sources is different from that of the X-ray-selected sample. Namely, the fraction of low-absorption sources is at least 2 times larger than that of X-ray selected sources in the CDFS. This is mostly due to the larger fraction of star-forming galaxies present among the X-ray-detected radio sources. If we investigate the distribution of intrinsic absorption among sources with L X > 1042 erg s -1 in the hard 2-10 keV band (therefore in the AGN luminosity regime), we find agreement between the X-ray population with and without radio emission. In general, radio-detected X-ray AGNs are not more heavily obscured than the non-radio-detected AGN. This argues against the use of radio surveys as an efficient way to search for the missing population of strongly absorbed AGNs. For the radio sources without cataloged X-ray counterparts, we measure their average photometric properties in the X-ray bands with stacking techniques. We detect emission with very high confidence level in the soft band and marginally in the hard band. Given their redshift distribution, the average X-ray luminosity of these sources is consistent with being powered by star formation. We note that on average, the spectral shape of our radio sources is soft with HR -0.5 and constant in different bins of radio flux. This result shows that the statistics do not indicate a significant trend in the average X-ray spectral properties, but it is consistent with the radio source population being dominated by star-forming galaxies below 100 μJy, as shown by our morphological and multiwavelength analysis presented in Mainieri et al. and Padovani et al..
AB - We discuss the X-ray properties of the radio sources detected in a deep 1.4 and 5 GHz VLA Radio survey of the Extended Chandra Deep Field-South (E-CDFS). Among the 266 radio sources detected, we find 89 sources (1/3 of the total) with X-ray counterparts in the catalog of the 1 Ms exposure of the central 0.08 deg2 or in the catalog of the 250 ks exposure of the 0.3 deg 2 E-CDFS field. For 76 (85%) of these sources, we have spectroscopic or photometric redshifts, and therefore we are able to derive their intrinsic properties from X-ray spectral analysis, namely intrinsic absorption and total X-ray luminosities. We find that the population of submillijansky radio sources with X-ray counterparts is composed of a mix of roughly 1/3 star-forming galaxies and 2/3 active galactic nuclei (AGNs). The distribution of intrinsic absorption among X-ray-detected radio sources is different from that of the X-ray-selected sample. Namely, the fraction of low-absorption sources is at least 2 times larger than that of X-ray selected sources in the CDFS. This is mostly due to the larger fraction of star-forming galaxies present among the X-ray-detected radio sources. If we investigate the distribution of intrinsic absorption among sources with L X > 1042 erg s -1 in the hard 2-10 keV band (therefore in the AGN luminosity regime), we find agreement between the X-ray population with and without radio emission. In general, radio-detected X-ray AGNs are not more heavily obscured than the non-radio-detected AGN. This argues against the use of radio surveys as an efficient way to search for the missing population of strongly absorbed AGNs. For the radio sources without cataloged X-ray counterparts, we measure their average photometric properties in the X-ray bands with stacking techniques. We detect emission with very high confidence level in the soft band and marginally in the hard band. Given their redshift distribution, the average X-ray luminosity of these sources is consistent with being powered by star formation. We note that on average, the spectral shape of our radio sources is soft with HR -0.5 and constant in different bins of radio flux. This result shows that the statistics do not indicate a significant trend in the average X-ray spectral properties, but it is consistent with the radio source population being dominated by star-forming galaxies below 100 μJy, as shown by our morphological and multiwavelength analysis presented in Mainieri et al. and Padovani et al..
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U2 - 10.1088/0004-637X/698/1/740
DO - 10.1088/0004-637X/698/1/740
M3 - Article
AN - SCOPUS:66649111915
SN - 0004-637X
VL - 698
SP - 740
EP - 755
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -