Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST

Peter Senchyna, Daniel P Stark, Alba Vidal-García, Jacopo Chevallard, Stéphane Charlot, Ramesh Mainali, Tucker Jones, Aida Wofford, Anna Feltre, Julia Gutkin

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

Nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z/2. Such tests are particularly important for interpreting the surprising highionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR ~102 Gyr-1). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z ~ 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H ≲ 8.0 (Z/Z ≲ 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.

Original languageEnglish (US)
Pages (from-to)2608-2632
Number of pages25
JournalMonthly Notices of the Royal Astronomical Society
Volume472
Issue number3
DOIs
StatePublished - 2017

Fingerprint

James Webb Space Telescope
reference sample
ultraviolet spectra
metallicity
stars
O stars
metal
stellar winds
dwarf galaxies
star formation rate
massive stars
metals
optical spectrum
ionization
energetics
vapor phases
galaxies
oxygen
photons
radiation

Keywords

  • Galaxies: evolution
  • Galaxies: stellar content
  • Stars: massive
  • Ultraviolet:galaxies

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST. / Senchyna, Peter; Stark, Daniel P; Vidal-García, Alba; Chevallard, Jacopo; Charlot, Stéphane; Mainali, Ramesh; Jones, Tucker; Wofford, Aida; Feltre, Anna; Gutkin, Julia.

In: Monthly Notices of the Royal Astronomical Society, Vol. 472, No. 3, 2017, p. 2608-2632.

Research output: Contribution to journalArticle

Senchyna, P, Stark, DP, Vidal-García, A, Chevallard, J, Charlot, S, Mainali, R, Jones, T, Wofford, A, Feltre, A & Gutkin, J 2017, 'Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST', Monthly Notices of the Royal Astronomical Society, vol. 472, no. 3, pp. 2608-2632. https://doi.org/10.1093/mnras/stx2059
Senchyna, Peter ; Stark, Daniel P ; Vidal-García, Alba ; Chevallard, Jacopo ; Charlot, Stéphane ; Mainali, Ramesh ; Jones, Tucker ; Wofford, Aida ; Feltre, Anna ; Gutkin, Julia. / Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST. In: Monthly Notices of the Royal Astronomical Society. 2017 ; Vol. 472, No. 3. pp. 2608-2632.
@article{4c71dbcaf0024d1b971ae4d5876aa8ae,
title = "Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST",
abstract = "Nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z⊙/2. Such tests are particularly important for interpreting the surprising highionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR ~102 Gyr-1). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z ~ 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H ≲ 8.0 (Z/Z⊙ ≲ 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.",
keywords = "Galaxies: evolution, Galaxies: stellar content, Stars: massive, Ultraviolet:galaxies",
author = "Peter Senchyna and Stark, {Daniel P} and Alba Vidal-Garc{\'i}a and Jacopo Chevallard and St{\'e}phane Charlot and Ramesh Mainali and Tucker Jones and Aida Wofford and Anna Feltre and Julia Gutkin",
year = "2017",
doi = "10.1093/mnras/stx2059",
language = "English (US)",
volume = "472",
pages = "2608--2632",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "3",

}

TY - JOUR

T1 - Ultraviolet spectra of extreme nearby star-forming regions - approaching a local reference sample for JWST

AU - Senchyna, Peter

AU - Stark, Daniel P

AU - Vidal-García, Alba

AU - Chevallard, Jacopo

AU - Charlot, Stéphane

AU - Mainali, Ramesh

AU - Jones, Tucker

AU - Wofford, Aida

AU - Feltre, Anna

AU - Gutkin, Julia

PY - 2017

Y1 - 2017

N2 - Nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z⊙/2. Such tests are particularly important for interpreting the surprising highionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR ~102 Gyr-1). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z ~ 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H ≲ 8.0 (Z/Z⊙ ≲ 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.

AB - Nearby dwarf galaxies provide a unique laboratory in which to test stellar population models below Z⊙/2. Such tests are particularly important for interpreting the surprising highionization ultraviolet (UV) line emission detected at z > 6 in recent years. We present HST/COS UV spectra of 10 nearby metal-poor star-forming galaxies selected to show He II emission in SDSS optical spectra. The targets span nearly a dex in gas-phase oxygen abundance (7.8 < 12 + logO/H < 8.5) and present uniformly large specific star formation rates (sSFR ~102 Gyr-1). The UV spectra confirm that metal-poor stellar populations can power extreme nebular emission in high-ionization UV lines, reaching CIII] equivalent widths comparable to those seen in systems at z ~ 6-7. Our data reveal a marked transition in UV spectral properties with decreasing metallicity, with systems below 12 + logO/H ≲ 8.0 (Z/Z⊙ ≲ 1/5) presenting minimal stellar wind features and prominent nebular emission in He II and C IV. This is consistent with nearly an order of magnitude increase in ionizing photon production beyond the He+-ionizing edge relative to H-ionizing flux as metallicity decreases below a fifth solar, well in excess of standard stellar population synthesis predictions. Our results suggest that often-neglected sources of energetic radiation such as stripped binary products and very massive O-stars produce a sharper change in the ionizing spectrum with decreasing metallicity than expected. Consequently, nebular emission in C IV and He II powered by these stars may provide useful metallicity constraints in the reionization era.

KW - Galaxies: evolution

KW - Galaxies: stellar content

KW - Stars: massive

KW - Ultraviolet:galaxies

UR - http://www.scopus.com/inward/record.url?scp=85030543326&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=85030543326&partnerID=8YFLogxK

U2 - 10.1093/mnras/stx2059

DO - 10.1093/mnras/stx2059

M3 - Article

AN - SCOPUS:85030543326

VL - 472

SP - 2608

EP - 2632

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 3

ER -