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New insight on the far-UV SED and He ii emission from low metallicity galaxies

Published online by Cambridge University Press:  04 June 2020

Daniel Schaerer Open the ORCID record for Daniel Schaerer [Opens in a new window] ,
Yuri Izotov  and
Tassos Fragos
Daniel Schaerer
Affiliation:
Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland email: [email protected] CNRS, IRAP, 14 Avenue E. Belin, 31400 Toulouse, France
Yuri Izotov
Affiliation:
Bogolyubov Institute for Theoretical Physics, National Academy of Sciences of Ukraine, 14-b Metrolohichna str., Kyiv, 03143, Ukraine
Tassos Fragos
Affiliation:
Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland email: [email protected]
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Abstract

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Understanding the ionizing spectrum of low-metallicity galaxies is of great importance for modeling and interpreting emission line observations of early/distant galaxies.

Although a wide suite of stellar evolution, atmosphere, population synthesis, and photoionization models, taking many physical processes into account now exist, all models face a common problem: the inability to explain the presence of nebular Heii emission, which is observed in many low metallicity galaxies, both in UV and optical spectra. Several possible explanations have been proposed in the literature, including Wolf-Rayet (WR) stars, binaries, very massive stars, X-ray sources, or shocks. However, none has so far been able to explain the major observations.

We briefly discuss the He ii problem, available empirical data, and observed trends combining X-ray, optical and other studies. We present a simple and consistent physical model showing that X-ray binaries could explain the long-standing nebular Heii problem. Our model, described in Schaerer et al. (2019), successfully explains the observed trends and strength of nebular He ii emission in large samples of low metallicity galaxies and in individual galaxies, which have been studied in detail and with multi-wavelength observations. Our results have in particular important implications for the interpretation of galaxy spectra in the early Universe, which will be obtained with upcoming and future facilities.

Keywords

galaxies: high-redshiftultraviolet: galaxies(ISM:) HII regionsX-rays: binaries
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 15 , Symposium S352: Uncovering Early Galaxy Evolution in the ALMA and JWST Era , June 2019 , pp. 79 - 83
Copyright
© International Astronomical Union 2020

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