X-ray properties of K-selected galaxies at 0.5 < z < 2.0: investigating trends with stellar mass, redshift and spectral type

Journal Article · Sat Mar 01 04:00:00 EST 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/783/1/25· OSTI ID:22351366

Jones, Therese M.; Kriek, Mariska ^[1]; Van Dokkum, Pieter G.; Whitaker, Katherine E. ^[2]; Brammer, Gabriel ^[3]; Franx, Marijn; Labbé, Ivo ^[4]

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1. Department of Astronomy, University of California, Berkeley, CA 94720 (United States)
2. Department of Astronomy, Yale University, New Haven, CT 06520-8101 (United States)
3. European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Vitacura, Santiago (Chile)
4. Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden (Netherlands)

We examine how the total X-ray luminosity correlates with stellar mass, stellar population, and redshift for a K-band limited sample of ∼3500 galaxies at 0.5 < z < 2.0 from the NEWFIRM Medium Band Survey in the COSMOS field. The galaxy sample is divided into 32 different galaxy types, based on similarities between the spectral energy distributions. For each galaxy type, we further divide the sample into bins of redshift and stellar mass, and perform an X-ray stacking analysis using the Chandra COSMOS data. We find that full band X-ray luminosity is primarily increasing with stellar mass, and at similar mass and spectral type is higher at larger redshifts. When comparing at the same stellar mass, we find that the X-ray luminosity is slightly higher for younger galaxies (i.e., weaker 4000 Å breaks), but the scatter in this relation is large. We compare the observed X-ray luminosities to those expected from low- and high-mass X-ray binaries (XRBs). For blue galaxies, XRBs can almost fully account for the observed emission, while for older galaxies with larger 4000 Å breaks, active galactic nuclei (AGN) or hot gas dominate the measured X-ray flux. After correcting for XRBs, the X-ray luminosity is still slightly higher in younger galaxies, although this correlation is not significant. AGN appear to be a larger component of galaxy X-ray luminosity at earlier times, as the hardness ratio increases with redshift. Together with the slight increase in X-ray luminosity this may indicate more obscured AGNs or higher accretion rates at earlier times.

• OSTI ID: 22351366
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 783; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
CORRELATIONS
EMISSION
EVOLUTION
GALAXY NUCLEI
LUMINOSITY
MASS
RED SHIFT
UNIVERSE
X RADIATION
X-RAY GALAXIES