University of Hertfordshire

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From the same journal

Documents

  • A. Saxena
  • R. S. Ellis
  • P. U. Forster
  • A. Calabro
  • L. Pentericci
  • A. C. Carnall
  • M. Castellano
  • F. Cullen
  • A. Fontana
  • M. Franco
  • J. P. U. Fynbo
  • A. Gargiulo
  • B. Garilli
  • N. P. Hathi
  • D. J. McLeod
  • G. Zamorani
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Original languageEnglish
Pages (from-to)4798–4812
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Volume505
Issue4
Early online date31 May 2021
DOIs
Publication statusPublished - 1 Aug 2021

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 (HMXBs) in 301 normal star-forming galaxies in the redshift range 3 < z < 5.5. Our analysis evaluates correlations between X-ray luminosities (LX), star formation rates (SFRs), and stellar metallicities (Z∗) 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 LX/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 LX/SFR to z ≃ 5 proceeds as (1 + z)1.03 ± 0.02. Using stellar metallicities derived from photospheric absorption features in our spectroscopic data, we confirm indications at lower redshifts that LX/SFR is stronger for metal-poor galaxies. We use semi-analytic models to show that metallicity dependence of LX/SFR alone may not be sufficient to fully explain the observed redshift evolution of X-ray emission from HMXBs, particularly for galaxies with SFR < 30 M⊙ yr-1. We speculate that reduced overall stellar ages and 'burstier' star formation histories in the early Universe may lead to higher LX/SFR for the same metallicity. We then define the redshift-dependent contribution of HMXBs to the integrated X-ray luminosity density and, in comparison with models, find that the contribution of HMXBs to the cosmic X-ray background at z > 6 may be ≳0.25 dex higher than previously estimated.

Notes

© The Author(s) 2021. Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/)

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