The Stellar-age Dependence of X-Ray Emission from Normal Star-forming Galaxies in the GOODS Fields
Journal
Date Issued
2022
Author(s)
Gilbertson, Woodrow
•
Lehmer, Bret D.
•
Doore, Keith
•
Eufrasio, Rafael T.
•
Basu-Zych, Antara
•
Brandt, William N.
•
Fragos, Tassos
•
Garofali, Kristen
•
Kovlakas, Konstantinos
•
Luo, Bin
•
•
•
Williams, Benjamin F.
•
Xue, Yongquan
Abstract
The Chandra Deep Field-South and North surveys (CDFs) provide unique windows into the cosmic history of X-ray emission from normal (nonactive) galaxies. Scaling relations of normal-galaxy X-ray luminosity (L X) with star formation rate (SFR) and stellar mass (M ∗) have been used to show that the formation rates of low-mass and high-mass X-ray binaries (LMXBs and HMXBs, respectively) evolve with redshift across z ≈ 0-2 following L HMXB/SFR α(1 + z) and L LMXB/M ∗ α(1 + z)2-3. However, these measurements alone do not directly reveal the physical mechanisms behind the redshift evolution of X-ray binaries (XRBs). We derive star formation histories for a sample of 344 normal galaxies in the CDFs, using spectral energy distribution (SED) fitting of FUV-to-FIR photometric data, and construct a self-consistent, age-dependent model of the X-ray emission from the galaxies. Our model quantifies how X-ray emission from hot gas and XRB populations vary as functions of host stellar-population age. We find that (1) the ratio L X/M ∗ declines by a factor of ∼1000 from 0 to 10 Gyr and (2) the X-ray SED becomes harder with increasing age, consistent with a scenario in which the hot gas contribution to the X-ray SED declines quickly for ages above 10 Myr. When dividing our sample into subsets based on metallicity, we find some indication that L X/M ∗ is elevated for low-metallicity galaxies, consistent with recent studies of X-ray scaling relations. However, additional statistical constraints are required to quantify both the age and metallicity dependence of X-ray emission from star-forming galaxies.
Volume
926
Issue
1
Start page
28
Issn Identifier
0004-637X
Ads BibCode
2022ApJ...926...28G
Rights
open.access
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