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Version: Accepted on May 27 2014

arXiv:1405.7039v1 [astro-ph.GA] 27 May 2014

Early-type galaxies in the Chandra COSMOS Survey F. Civano1,2,3, G. Fabbiano2, S. Pellegrini4 , D-W. Kim2 , A. Paggi2 , R. Feder5 and M. Elvis2 ABSTRACT We study a sample of 69 X-ray detected Early Type Galaxies (ETGs), selected from the Chandra COSMOS survey, to explore the relation between the X-ray luminosity of hot gaseous halos (LX,gas ) and the integrated stellar luminosity (LK ) of the galaxies, in a range of redshift extending out to z=1.5. In the local universe a tight steep relationship has been stablished between these two quantities (LX,gas ∼ L4.5 K ) suggesting the presence of largely virialized halos in X-ray luminous systems. We use well established relations from the study of local universe ETGs, together with the expected evolution of the X-ray emission, to subtract the contribution of low mass X-ray binary populations (LMXBs) from the X-ray luminosity of our sample. Our selection minimizes the presence of active galactic nuclei (AGN), yielding a sample representative of normal passive COSMOS ETGs; therefore the resulting luminosity should be representative of gaseous halos, although we cannot exclude other sources such as obscured AGN, or enhanced X-ray emission connected with embedded star formation in the higher z galaxies. We find that most of the galaxies with estimated LX