# University of Hertfordshire

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

Research output: Contribution to journalArticlepeer-review

• 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
Original language English Monthly Notices of the Royal Astronomical Society Submitted - 6 Apr 2021

### Abstract

We use VANDELS spectroscopic data overlapping with the $\simeq$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 $3 <z <5.5$. Our analysis evaluates correlations between X-ray luminosities ($L_X$), star formation rates (SFR) and stellar metallicities ($Z_\star$) 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 $L_X$/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 $L_X$/SFR to $z\simeq5$ proceeds as $(1 + z)^{1.03 \pm 0.02}$. Using stellar metallicities derived from photospheric absorption features in our spectroscopic data, we confirm indications at lower redshifts that $L_X$/SFR is stronger for metal-poor galaxies. We use semi-analytic models to show that metallicity dependence of $L_X$/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 $6$ may be $\gtrsim 0.25$ dex higher than previously estimated.

ID: 24967164