paper

The VANDELS Survey: New constraints on the high-mass X-ray binary populations in normal star-forming galaxies at 3 < z < 5.5

arXiv:2104.02624 · doi:10.1093/mnras/stab1575

Abstract

We use VANDELS spectroscopic data overlapping with the 7 Ms Chandra Deep Field South survey to extend studies of high-mass X-ray binary systems (XRBs) in 301 normal star-forming galaxies in the redshift range . Our analysis evaluates correlations between X-ray luminosities (), star formation rates (SFR) and stellar metallicities () to higher redshifts and over a wider range in galaxy properties than hitherto. Using a stacking analysis performed in bins of both redshift and SFR for sources with robust spectroscopic redshifts without AGN signatures, we find convincing evolutionary trends in the ratio /SFR to the highest redshifts probed, with a stronger trend for galaxies with lower SFRs. Combining our data with published samples at lower redshift, the evolution of /SFR to proceeds as . Using stellar metallicities derived from photospheric absorption features in our spectroscopic data, we confirm indications at lower redshifts that /SFR is stronger for metal-poor galaxies. We use semi-analytic models to show that metallicity dependence of /SFR alone may not be sufficient to fully explain the observed redshift evolution of X-ray emission from high-mass XRBs, particularly for galaxies with SFR yr. We speculate that the discrepancy may arise due to reduced overall stellar ages in the early Universe leading to higher /SFR for the same metallicity. We use our data to define the redshift-dependent contribution of XRBs to the integrated X-ray luminosity density and, in comparison with models, find that the contribution of high-mass XRBs to the cosmic X-ray background at may be dex higher than previously estimated.

16 pages, 10 figures, Published in MNRAS

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