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标题：X-ray binaries as the origin of nebular He  II emission in low-metallicity star-forming galaxies
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作者：D. Schaerer ; T. Fragos ; Y. I. Izotov 等
期刊名称：Astronomy & Astrophysics
印刷版ISSN：0004-6361
电子版ISSN：1432-0746
出版年度：2019
卷号：622
DOI：10.1051/0004-6361/201935005
语种：English
出版社：EDP Sciences
摘要：The origin of nebular He IIemission, which is frequently observed in low-metallicity (O/H) star-forming galaxies, remains largely an unsolved question. Using the observed anticorrelation of the integrated X-ray luminosity per unit of star formation rate (LX/SFR) of an X-ray binary population with metallicity and other empirical data from the well-studied galaxy I Zw 18, we show that the observed He II λ4686 intensity and its trend with metallicity is naturally reproduced if the bulk of He+ionizing photons are emitted by the X-ray sources. We also show that a combination of X-ray binary population models with normal single and/or binary stellar models reproduces the observedI(4686)/I(Hβ) intensities and its dependency on metallicity and age. We conclude that both empirical data and theoretical models suggest that high-mass X-ray binaries are the main source of nebular He IIemission in low-metallicity star-forming galaxies.
关键词：engalaxies: ISMgalaxies: high-redshiftX-rays: binaries