Multicolor Photometric Observations of Candidate Optical Counterparts toROSATFaint X-Ray Sources in a 1 Square Degree Field of the BATC Survey

We present optical candidates for 75 X-ray sources in a $\sim 1$ deg$^2$overlapping region with the medium deep ROSAT survey. These candidates areselected using the multi-color CCD imaging observations made for the T329 fieldof the Beijing-Arizona-Taipei-Connecticut (BATC) Sky Survey. These X-raysources are relatively faint (CR $<< 0.2 s^{-1}$) and thus mostly are notincluded in the RBS catalog, they also remain as X-ray sources without opticalcandidates in a previous identification program carried out by the HamburgQuasar Survey. Within their position-error circles, almost all the X-raysources are observed to have one or more spatially associated opticalcandidates within them down to the magnitude $m_V \sim 23.1$. We haveclassified 149 of 156 detected optical candidates with 73 of the 75 X-raysources with a SED-based Object Classification Approach (SOCA). These opticalcandidates include: 31 QSOs, 39 stars, 37 starburst galaxies, 42 galaxies, and7 "just" visible objects. We have also cross-correlated the positions of theseoptical objects with NED, the FIRST radio source catalog and the 2MASS catalog.Separately, we have also SED-classified the remaining 6011 objects in our fieldof view. Optical objects are found at the $6.5\sigma$ level above what onewould expect from a random distribution, only QSOs are over-represented inthese error circles at greater than 4$\sigma$ frequency. We estimate redshiftsfor all extragalactic objects, and find a good correspondence of our predictedredshift with the measured redshift (a mean error of 0.04 in $\Delta z$. Thereappears to be a supercluster at z $\sim$ 0.3-0.35 in this direction, includingmany of the galaxies in the X-ray error circles are found in this redshiftrange.