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

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2203.16566.pdf (1.7 MB)

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https://arxiv.org/abs/2203.16566

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http://hdl.handle.net/11603/24680

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)
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https://orcid.org/0000-0001-8525-4920

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2022-04-01

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journal articles
preprints
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This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Abstract

High-energy emission associated with star formation has been proposed as a significant source of interstellar medium (ISM) ionization in low-metallicity starbursts and an important contributor to the heating of the intergalactic medium (IGM) in the high-redshift (z>8) Universe. Using Chandra observations of a sample of 30 galaxies at D≈~200--450 Mpc that have high specific star-formation rates of 3--9 Gyr−1 and metallicities near Z≈0.3Z⊙, we provide new measurements of the average 0.5--8 keV spectral shape and normalization per unit star-formation rate (SFR). We model the sample-combined X-ray spectrum as a combination of hot gas and high-mass X-ray binary (HMXB) populations and constrain their relative contributions. We derive scaling relations of logLHMXB0.5−8keV/SFR =40.19±0.06 and logLgas0.5−2keV/SFR =39.58+0.17−0.28; significantly elevated compared to local relations. The HMXB scaling is also somewhat higher than LHMXB0.5−8keV-SFR-Z relations presented in the literature, potentially due to our galaxies having relatively low HMXB obscuration and young and X-ray luminous stellar populations. The elevation of the hot gas scaling relation is at the level expected for diminished attenuation due to a reduction of metals; however, we cannot conclude that an Lgas0.5−2keV-SFR-Z relation is driven solely by changes in ISM metal content. Finally, we present SFR-scaled spectral models (both emergent and intrinsic) that span the X-ray--to--IR band, providing new benchmarks for studies of the impact of ISM ionization and IGM heating in the early Universe.