PREPRINT
1D752CBD-F93D-4248-B77C-66B8E812159A

Properties of Primitive Galaxies

Sara R. Heap, I. Hubeny, J. -C. Bouret, T. Lanz, J. Brinchmann
arXiv:2207.04553

Submitted on 10 July 2022

Abstract

We report on a study of 9 nearby star-forming, very low-metallicity galaxies observed by Hubble's COS far-UV spectrograph that can serve as templates of high-z galaxies to be observed by JWST. We find that the nebular spectra of these primitive galaxies show evidence of irradiation by X-ray emitters. Following Thuan et al. (2004), we identify the sources of X-ray emission as massive X-ray binaries containing a massive accreting stellar black hole. We further find that the lower the metallicity, the higher the probability of strong X-irradiation. Following Heger et al. (2003), we suggest that these accreting black holes are produced by direct collapse of stars having initial masses greater than $\sim 50\phantom{\rule{0.167em}{0ex}}{M}_{\odot }$. Our models of young star clusters with an embedded stellar black hole produce effects on the surrounding gaseous medium that are consistent with the observed spectra. We conclude that primitive galaxies are qualitatively different from more metal-rich galaxies in showing evidence of hard radiation that can best be explained by the presence of one or more embedded stellar black holes.

Preprint

Comment: 6 pages, 4 figures

Subjects: Astrophysics - Astrophysics of Galaxies; Astrophysics - Cosmology and Nongalactic Astrophysics; Astrophysics - Solar and Stellar Astrophysics