The Evolution of Normal Galaxy X-Ray Emission Through Cosmic History: Constraints From the 6 MS Chandra Deep Field-South

Abstract

We present measurements of the evolution of normal-galaxy X-ray emission from z ≈ 0-7 using local galaxies and galaxy samples in the ≈6 Ms Chandra Deep Field-South (CDF-S) survey. The majority of the CDF-S galaxies are observed at rest-frame energies above 2 keV, where the emission is expected to be dominated by X-ray binary (XRB) populations; however, hot gas is expected to provide small contributions to the observedframe < ∼ 1 keV emission at z < ∼ 1. We show that a single scaling relation between X-ray luminosity (L X ) and star-formation rate (SFR) is insufficient for characterizing the average X-ray emission at all redshifts. We establish that scaling relations involving not only SFR, but also stellar mass (M ⋆ ) and redshift, provide significantly improved characterizations of the average X-ray emission from normal galaxy populations at z ≈ 0-7. We further provide the first empirical constraints on the redshift evolution of X-ray emission from both low-mass XRB (LMXB) and high-mass XRB (HMXB) populations and their scalings with M ⋆ and SFR, respectively. We find L 2−10 keV (LMXB)/M ⋆ ∝ (1 + z) 2−3 and L 2−10 keV (HMXB)/SFR ∝ (1 + z), and show that these relations are consistent with XRB population-synthesis model predictions, which attribute the increase in LMXB and HMXB scaling relations with redshift as being due to declining host galaxy stellar ages and metallicities, respectively. We discuss how emission from XRBs could provide an important source of heating to the intergalactic medium in the early Universe, exceeding that of active galactic nuclei.

X-rays across the galaxy population – II. The distribution of AGN accretion rates as a function of stellar mass and redshift

“…M12 apply corrections based on locally-calibrated scaling relations (Ranalli et al 2003), whereas we apply a larger correction based on our work in Paper I that indicates a larger X-ray luminosity per unit SFR at these redshifts (see also Lehmer et al 2016). Our measurements still reveal a clear "AGN main sequence" at z ∼ 2, although there are indications that the slope may be steeper than unity due to a suppression of AGN activity at lower stellar masses.…”

Probing Large-scale Coherence between Spitzer IR and Chandra X-Ray Source-subtracted Cosmic Backgrounds

“…where α, β, γ and δ are parameters for which we adopt the values measured by Lehmer et al (2016) in both the soft and hard band, and include the intrinsic scatter in the relation. For the underlying galaxy population we use a semi-analytic galaxy formation model based on the Millennium simulation (Henriques et al 2015), which is in good agreement with the observed star formation history and stellar mass function as a function of redshift.…”

High-redshift AGN in the Chandra Deep Fields: the obscured fraction and space density of the sub-L* population

“…Using more conservative criteria, such as requiring that the 1 The integrated X-ray emission from high-mass and low-mass XRB in a galaxy can reach luminosities of logL X ≈ 42 (i.e. Lehmer et al 2016). At z > 3, the flux limit of the 7 Ms CDF-S corresponds to logL X 42.…”

“…19 (right panel) is the XLF of star-forming galaxies at z = 4, where the emission is mostly due to high-mass XRB, from the model by Volonteri et al (2017, see in particular their section 2.2 for assumptions and caveats). Briefly, they mapped the stellar-mass functions of Song et al (2016) into an XLF through the mainsequence of star-forming galaxies (Salmon et al 2015) and the SFR-LX scaling relation by Fragos et al (2013, model 269), which Lehmer et al (2016) demonstrated to be the best representation at z = 0 − 2.5. At logLX 42.5, the luminosity limit we applied to our luminosity functions, as the 42 logLX 42.5 regime was strongly affected by incompleteness, the density of star-forming galaxies is a factor Figure 19.…”