TY - JOUR
T1 - Extremely metal-poor galaxies with HST/COS
T2 - Laboratories for models of low-metallicity massive stars and high-redshift galaxies
AU - Senchyna, Peter
AU - Stark, Daniel P.
AU - Chevallard, Jacopo
AU - Charlot, Stéphane
AU - Jones, Tucker
AU - Vidal-García, Alba
N1 - Publisher Copyright:
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
PY - 2019/9/21
Y1 - 2019/9/21
N2 - Ultraviolet (UV) observations of local star-forming galaxies have begun to establish an empirical baseline for interpreting the rest-UV spectra of reionization-era galaxies. However, existing high-ionization emission line measurements at z > 6 (WC IV,0 ≳ 20 Å) are uniformly stronger than observed locally (WC IV,0 ≲ 2 Å), likely due to the relatively high metallicities (Z/Z☉ > 0.1) typically probed by UV surveys of nearby galaxies. We present new HST/COS spectra of six nearby (z < 0.01) extremely metal-poor galaxies (XMPs, Z/Z☉ ≲ 0.1) targeted to address this limitation and provide constraints on the highly uncertain ionizing spectra powered by low-metallicity massive stars. Our data reveal a range of spectral features, including one of the most prominent nebular C IV doublets yet observed in local star-forming systems and strong He II emission. Using all published UV observations of local XMPs to date, we find that nebular C IV emission is ubiquitous in very high specific star formation rate systems at low metallicity, but still find equivalent widths smaller than those measured in individual lensed systems at z > 6. Our moderate-resolution HST/COS data allow us to conduct an analysis of the stellar winds in a local nebular C IV emitter, which suggests that some of the tension with z > 6 data may be due to existing local samples not yet probing sufficiently high α/Fe abundance ratios. Our results indicate that C IV emission can play a crucial role in the JWST and ELT era by acting as an accessible signpost of very low metallicity (Z/Z☉ < 0.1) massive stars in assembling reionization-era systems.
AB - Ultraviolet (UV) observations of local star-forming galaxies have begun to establish an empirical baseline for interpreting the rest-UV spectra of reionization-era galaxies. However, existing high-ionization emission line measurements at z > 6 (WC IV,0 ≳ 20 Å) are uniformly stronger than observed locally (WC IV,0 ≲ 2 Å), likely due to the relatively high metallicities (Z/Z☉ > 0.1) typically probed by UV surveys of nearby galaxies. We present new HST/COS spectra of six nearby (z < 0.01) extremely metal-poor galaxies (XMPs, Z/Z☉ ≲ 0.1) targeted to address this limitation and provide constraints on the highly uncertain ionizing spectra powered by low-metallicity massive stars. Our data reveal a range of spectral features, including one of the most prominent nebular C IV doublets yet observed in local star-forming systems and strong He II emission. Using all published UV observations of local XMPs to date, we find that nebular C IV emission is ubiquitous in very high specific star formation rate systems at low metallicity, but still find equivalent widths smaller than those measured in individual lensed systems at z > 6. Our moderate-resolution HST/COS data allow us to conduct an analysis of the stellar winds in a local nebular C IV emitter, which suggests that some of the tension with z > 6 data may be due to existing local samples not yet probing sufficiently high α/Fe abundance ratios. Our results indicate that C IV emission can play a crucial role in the JWST and ELT era by acting as an accessible signpost of very low metallicity (Z/Z☉ < 0.1) massive stars in assembling reionization-era systems.
KW - Galaxies: evolution
KW - Galaxies: stellar content
KW - Stars: massive
KW - Ultraviolet: galaxies
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U2 - 10.1093/mnras/stz1907
DO - 10.1093/mnras/stz1907
M3 - Article
AN - SCOPUS:85075252169
SN - 0035-8711
VL - 488
SP - 3492
EP - 3506
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -