The VANDELS Survey: new constraints on the high-mass X-ray binary populations in normal star-forming galaxies at 3 z < 5.5. Issue 4 (31st May 2021)

• Record Type: Journal Article
• Authors: Saxena, A; Ellis, R S; Förster, P U; Calabrò, A; Pentericci, L; Carnall, A C; Castellano, M; Cullen, F; Fontana, A; Franco, M; Fynbo, J P U; Gargiulo, A; Garilli, B; Hathi, N P; McLeod, D J; Amorín, R; Zamorani, G
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 505:Issue 4(2021)
• Page Start: 4798
• Page End: 4812
• Publication Date: 2021-05-31
• Subjects: galaxies: evolution -- galaxies: high-redshift -- X-rays: binaries; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab1575
• Languages: English
• ISSNs: 0035-8711

Abstract

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 &lt; z &lt; 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 &lt; 30 M⊙ yr −1 . We speculate that reduced overall stellar ages and &#39;burstier&#39; 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 &gt; 6 may be ≳0.25 dex higher than previously estimated.