Francesca Civano (Dartmouth College and SAO ) : Finding rare sources in the C-COSMOS survey

The C-COSMOS survey is a 1.8 Ms Chandra program that has imaged the center of the COSMOS field to a depth of Fx=2e-16 (cgs unit). Visual inspection of the HST/ACS images of the 1761 bC-COSMOS X-ray sources led to the serendipitous discovery of a, so far unique, source at z=0.359 (CID-42). CID-42 is a peculiar source in 3 ways: It is the only source out of 2700 X-ray detections clearly showing two sources resolved in the HST image embedded in the same galaxy. In the optical spectra, a velocity offset larger than 1000 km/s is measured between the broad and narrow component of Hb line. Recently awarded high resolution Chandra data reveal that the X-ray emission detected in CID-42 arises from only the point-like optical source, with a 3sigma upper limit of 4% on the observed X-ray flux from the other source. A good explanation for CID-42 would link all these features. We propose a GW recoil scenario, where the point like sources is moving away from the galaxy at a very high velocity. Models developed using hydrodynamic galaxy merger simulations, coupled with radiative transfer calculations, help to constrain the likelihood of this scenario. The recently approved X-ray visionary project to fully cover the COSMOS field with Chandra is definetely the best place where to find more of these rare sources.