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Elevated Hot Gas and High-Mass X-ray Binary Emission in Low Metallicity Galaxies: Implications for Nebular Ionization and Intergalactic Medium Heating in the Early Universe

Presentation #403.02 in the session “Implications and Tracers of the Energetic Processes at Cosmic Dawn”.

Published onApr 01, 2022
Elevated Hot Gas and High-Mass X-ray Binary Emission in Low Metallicity Galaxies: Implications for Nebular Ionization and Intergalactic Medium Heating in the Early Universe

High-energy emission from X-ray binaries and hot gas has been proposed as a significant source of interstellar medium (ISM) ionization in low-metallicity starburst galaxies and an important contributor to the heating of the intergalactic medium (IGM) in the high-redshift (z ≳ 8) Universe. We will present new Chandra and multiwavelength constraints on the average IR-to-X-ray SED of 30 low metallicity (~0.3 solar metallicity) galaxies in the relatively nearby Universe (D = 200-450 Mpc). We examine the relative contributions of hot gas and high-mass X-ray binary (HMXB) emission to the SED and measure their X-ray scaling relations with galaxy star-formation rate (SFR). We will show that LX/SFR for both hot gas and HMXB emission is elevated in these low-metallicity galaxies relative to more typical (and higher metallicity) local galaxies, and we will provide interpretations for this metallicity dependence. Finally, we will show that interpolation of our intrinsic SED models into the extreme UV can yield an ionizing photon flux (at 0.01-0.5 keV) much larger than recent studies have estimated, supporting the idea that X-ray emitting sources may be viable candidates for producing high-ionization nebular emission lines (e.g., HeII, OIV, and CIV), most often seen in metal-poor galaxies.


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