X-ray Luminosity Evolution in Normal Elliptical Galaxies with c-COSMOS
Dong-Woo Kim (cfa) , G. Fabbiano (cfa), M. Elvis (cfa), T. Aldcroft (cfa), H. Brunner (mpg), M. Brusa (mpg), N. Cappelluti (mpg), F. Civano (bo), A. Comastri (bo), A. Finoguenov (mpg), F. Fiore (inaf), A. Fruscione (cfa), R. Gilli (bo), T. Miyaji (cmu), S. Puccetti (asdc), C. Vignali (inaf), G. Zamorani (inaf), C. M. Carollo (ETH-Zurich), S. Lilly (ETH-Zurich), C. Scarlata (ETH-Zurich), P. Oesch (ETH-Zurich), M. Sargent (ETH-Zurich), R. Feldmann (ETH-Zurich)
We investigate the X-ray luminosity of a well-defined sample of early type galaxies as a function of redshift with Chandra COSMOS data (Elvis et al. 2006). We carefully select high-redshift elliptical galaxies, based on their morphology, optical color, and the Kormendy relation (Scarlata et al. 2007). By stacking X-ray data at the positions of elliptical galaxies after excluding possible AGNs, we find that the average LX / LB increases by a factor of 2 to z=0.4 (or lookback time of 5 Gyr), at a 3 sigma confidence level. This increase is slightly steeper than that expected from the previously determined (1+z)2.7, but still consistent within the error. We also discuss the X-ray luminosity and its evolution in S0, E+A, optically (less-) luminous galaxy samples.