X-ray Emission in Non-AGN Galaxies at z ~ 1

TL;DR

This study analyzes X-ray emission in non-AGN galaxies at z ~ 1, revealing a correlation with stellar mass in the soft band and characterizing the nature of the X-ray emission through spectral modeling.

Contribution

It provides the first detailed analysis of X-ray emission in non-AGN galaxies at z ~ 1, establishing a relation between X-ray counts and stellar mass and exploring the spectral origins of the emission.

Findings

Significant correlation between X-ray counts and stellar mass in the soft band.

X-ray luminosities range from 10^39 to 8x10^40 ergs/s.

No correlation found in hard and ultra-hard X-ray bands.

Abstract

Using data from the DEEP2 galaxy redshift survey and the All Wavelength Extended Groth Strip International Survey we obtain stacked X-ray maps of galaxies at 0.7 < z < 1.0 as a function of stellar mass. We compute the total X-ray counts of these galaxies and show that in the soft band (0.5--2,kev) there exists a significant correlation between galaxy X-ray counts and stellar mass at these redshifts. The best-fit relation between X-ray counts and stellar mass can be characterized by a power law with a slope of 0.58 +/- 0.1. We do not find any correlation between stellar mass and X-ray luminosities in the hard (2--7,kev) and ultra-hard (4--7,kev) bands. The derived hardness ratios of our galaxies suggest that the X-ray emission is degenerate between two spectral models, namely point-like power-law emission and extended plasma emission in the interstellar medium. This is similar to what has been observed in low redshift galaxies. Using a simple spectral model where half of the emission comes from power-law sources and the other half from the extended hot halo we derive the X-ray luminosities of our galaxies. The soft X-ray luminosities of our galaxies lie in the range 10^39-8x10^40, ergs/s. Dividing our galaxy sample by the criteria U-B > 1, we find no evidence that our results for X-ray scaling relations depend on optical color.