2020/11/18 by Bret Lehmer, Bret D. Lehmer, Rafael T. Eufrasio +12 · 89 citations
Physics and Astronomy · #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Binary number #Function (biology) #Galaxies: Formation, Evolution, Phenomena #Galaxy #High mass #Luminosity #Luminosity function #Metallicity #Neutron star #Physics #Pulsars and Gravitational Waves Research #Star formation #Stars #Stellar mass #X-ray binary #astro-ph.CO #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/abcec1
published in The Astrophysical Journal 907(1), 17 (IOP Publishing) · Accepted for publication in ApJ
arxiv created 2020/11/18 · openalex publication_date 2021/01/01 · arxiv updated 2021/01/27 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/08
Abstract In this work, we present detailed constraints on the metallicity dependence of the high-mass X-ray binary (HMXB) X-ray luminosity function (XLF). We analyze ≈5 Ms of Chandra data for 55 actively star-forming galaxies at D ≲ 30 Mpc, with gas-phase metallicities spanning ≈ 7–9.2. Within the galactic footprints, our sample contains a total of 1311 X-ray point sources, of which ≈49% are expected to be HMXBs, with the remaining sources likely to be low-mass X-ray binaries (LMXBs; ≈22%) and unrelated background sources (≈29%). We construct a model that successfully characterizes the average HMXB XLF over the full metallicity range. We demonstrate that the SFR-normalized HMXB XLF shows clear trends with metallicity, showing steadily increasing numbers of luminous and ultraluminous X-ray sources ( (erg s −1 ) = 38–40.5) with declining metallicity. However, we find that the low-luminosity ( (erg s −1 ) = 36–38) HMXB XLF appears to show a nearly constant SFR scaling and slope with metallicity. Our model provides a revised scaling relation of integrated L X /SFR versus , and a new characterization of its SFR-dependent stochastic scatter. The general trend of this relation is broadly consistent with past studies based on integrated galaxy emission; however, our model suggests that this relation is driven primarily by the high-luminosity end of the HMXB XLF. Our results have implications for binary population synthesis models, the nature of super-Eddington accreting objects (e.g., ultraluminous X-ray sources), recent efforts to identify active galactic nucleus candidates in dwarf galaxies, and the X-ray radiation fields in the early universe during the epoch of cosmic heating at z ≳ 10.