X-ray Identifications of FIRST Radio Sources in the xBootes Field
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With the goal of investigating the nature and the environment of the faint radio sources (at mJy level), here are presented results of X-ray dentifications of Faint Imaging Radio Survey at Twenty centimetres (FIRST) in the 9 square degrees Bootes field of the NOAO Deep Wide Field Survey (NDWFS), using data from the Chandra XBootes survey. A total of 92 (10%) FIRST radio sources are identified above the X-ray flux limit f_X (0.5-7) keV = 8×10^{-15} erg s^{-1} cm^{-2}, and 79 optical counterparts are common to both the radio and X-ray sources. Spectroscopic identifications were available for 22 sources (27%). Multi-wavelength optical/infrared photometric data (Bw~25.5 mag, R~25.8 mag, I~25.5 mag and K~19.4 mag) were available for this field and were used to derive photometric redshift for the remaining 57 sources without spectroscopic information. Most of the radio-X-ray matches are optically extended objects in the R band with a photometric redshift distribution peaking at z~0.7. Based on the hardness ratio and X-ray luminosity, 37 sources (89%) were classified as AGN-1, 19 as AGN-2, 12 as QSO-1, 2 as QSO-2 and 9 sources as normal galaxies. While the majority of these sources have a hard X-ray luminosity L_X(2-7) keV >10^{42} erg s^{-1}, about one third of the sources have L_X(2-7) keV >10^{44} erg s^{-1} and therefore classified as QSO-1. The majority (68%) of the radio-X-ray matched population are found to have -1<log l_X/f_opt<1, region indicative of AGNs, 23% with high X-ray-to-optical flux ratio (log f_X/f_opt > 1), suggesting high redshift and/or dust obscured AGN, and 11% of the radio-X-ray matches that are X-ray faint optically bright sources with log f_X/f_opt <-1, and most of these sources are optically extended. These objects are low-z, normal galaxies or low luminosity AGNs (LINERS).
