Early-type galaxies in the Chandra COSMOS Survey

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 (L_X, gas) and the integrated stellar luminosity (L_K) 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 (L_X,gas~ L_K^4.5) 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 L_X<10^42 erg/s and z<0.55 follow the L_X,gas- L_K relation of local universe ETGs. For these galaxies, the gravitational mass can be estimated with a certain degree of confidence from the local virial relation. However, the more luminous (10^42<L_X<10^43.5 erg/s) and distant galaxies present significantly larger scatter; these galaxies also tend to have younger stellar ages. The divergence from the local L_X,gas - L_K relation in these galaxies implies significantly enhanced X-ray emission, up to a factor of 100 larger than predicted from the local relation. We discuss the implications of this result for the presence of hidden AGN, and the evolution of hot halos, in the presence of nuclear and star formation feedback.

29 pages, 10 figures, accepted for publication on ApJ on May 27 2014

References in corpus (8)

• COSMOS Photometric Redshifts with 30-bands for 2-deg2
• UltraVISTA: a new ultra-deep near-infrared survey in COSMOS
• The Chandra COSMOS Survey, I: Overview and Point Source Catalog
• Weak Gravitational Lensing with COSMOS: Galaxy Selection and Shape Measurements
• Comparing GC and Field LMXBs in Elliptical Galaxies with deep Chandra and Hubble data
• The X-ray Properties of Early-Type Galaxies in the Extended Chandra Deep Field-South
• The Chandra View of Galaxy Mergers
• The galaxy luminosity function and its evolution with Chandra

Cited by in corpus (6)

• The Chandra COSMOS-Legacy survey: Source X-ray spectral properties
• Constraining the UV emissivity of AGN throughout cosmic time via X-ray surveys
• A large sample of Kohonen selected E+A (post-starburst) galaxies from the Sloan Digital Sky Survey
• The connection between star formation and supermassive Black Hole activity in the local Universe
• X-ray luminosity-star formation rate scaling relation: Constraints from the eROSITA Final Equatorial Depth Survey (eFEDS)
• Connections between Central Intensity Ratio and hot gas properties of early-type galaxies