X-ray Luminosity Functions of Normal Galaxies in the GOODS

TL;DR

This study analyzes the X-ray luminosity functions of normal galaxies in the GOODS fields at different redshifts, revealing significant evolution and providing new models for galaxy X-ray emission over cosmic time.

Contribution

It introduces a detailed analysis of galaxy XLFs at z~0.25 and 0.75, applying advanced fitting techniques and models to understand their evolution.

Findings

XLFs differ significantly between z<0.5 and z>0.5

Best-fit luminosity evolution follows (1+z)^1.6 for early-type and (1+z)^2.3 for late-type galaxies

Models are robust across different functional forms

Abstract

We present soft (0.5-2 keV) X-ray luminosity functions (XLFs) in the Great Observatories Origins Deep Survey (GOODS) fields, derived for galaxies at z~0.25 and 0.75. SED fitting was used to estimate photometric redshifts and separate galaxy types, resulting in a sample of 40 early-type galaxies and 46 late-type galaxies. We estimate k-corrections for both the X-ray/optical and X-ray/NIR flux ratios, which facilitates the separation of AGN from the normal/starburst galaxies. We fit the XLFs with a power-law model using both traditional and Markov-Chain Monte Carlo (MCMC) procedures. The XLFs differ between z<0.5 and z>0.5, at >99% significance levels for early-type, late-type and all (early and late-type) galaxies.We also fit Schechter and log-normal models to the XLFs, fitting the low and high redshift XLFs for a given sample simultaneously assuming only pure luminosity evolution. In the case of log-normal fits, the results of MCMC fitting of the local FIR luminosity function were used as priors for the faint and bright-end slopes (similar to ``fixing'' these parameters at the FIR values except here the FIR uncertainty is included). The best-fit values of the change in log L* with redshift were dlogL* = 0.23 +/- 0.16 dex (for early-type galaxies) and 0.34 +/- 0.12 dex (for late-type galaxies), corresponding to (1+z)^1.6 and (1+z)^2.3. These results were insensitive to whether the Schechter or log-normal function was adopted.