X-ray Identifications of FIRST Radio Sources in the xBootes Field
  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 = 8x10^{-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).
