ChandraMultiwavelength Project: Normal Galaxies at Intermediate Redshift

(abridged) We have investigated 136 Chandra extragalactic sources withoutbroad optical emission lines, including 93 galaxies with narrow emission lines(NELG) and 43 with only absorption lines (ALG). Based on fx/fo, Lx, X-rayspectral hardness and optical emission line diagnostics, we have conservativelyclassified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. Wefound no statistically significant evolution in Lx/LB, within the limited zrange. We have built log(N)-log(S), after correcting for completeness based ona series of simulations. The best-fit slope is -1.5 for both S and B energybands, which is considerably steeper than that of the AGN-dominated cosmicbackground sources, but slightly flatter than the previous estimate, indicatingnormal galaxies will not exceed the AGN population until fx ~ 2 x 10-18 erg s-1cm-2 (a factor of ~5 lower than the previous estimate). A group of NELGs appearto be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correctingfor intrinsic absorption, their X-ray luminosities could be Lx > 10^44 erg s-1,making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG -X-ray bright, optically normal galaxy candidates) do not appear to besignificantly absorbed, we found two heavily obscured objects, which could beas luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+Agalaxy candidates with strong Balmer absorption lines, but no [OII] line. TheX-ray spectra of both galaxies are soft and one of them has a nearby closecompanion galaxy, supporting the merger/interaction scenario rather than thedusty starburst hypothesis.Comment: 31 pages, 9 figures, accepted for publication in ApJ (20 June 2006, v644), replaced with minor correction