The extended HeIIλ4686 emission in the extremely metal-poor galaxy SBS 0335-052E seen with MUSE★

Kehrig, C.; Vı́lchez, J. M.; Guerrero, M. A.; Iglésias-Páramo, J.; Hunt, L. K.; Puertas, S. Duarte; Ramos-Larios, G.

doi:10.1093/mnras/sty1920

Cited by 57 publications

(72 citation statements)

References 108 publications

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“…It is also one of most well-studied. Although it is farther and more metal-rich than the prototypical, I Zw 18, which is located at ∼18.2 Mpc (Aloisi et al 2007) and whose North-Western component has 12+log(O/H)=7.17 ± 0.04 (Skillman & Kennicutt 1993), the integrated He luminosity of SBS 0335-052E (1.87e39 erg s −1 , Kehrig et al 2018) is larger than that of I Zw 18 (1.12e38 s −1 , Kehrig et al 2015). This makes of SBS 0335-052E a unique target to test spectral synthesis models.…”

Section: Introductionmentioning

confidence: 91%

“…As described in , to correct for this, the resulting output sky-spectra from the DRS were first modified by interpolation over the affected wavelengths and subsequently fed into a second iteration of muse_scipost, as input sky-spectra. The uncorrected MUSE datacube was exploited by Kehrig et al (2018) to show that the total He flux of the galaxy, including regions outside of our aperture, can only be produced by either single, rotating metal-free stars or a binary population with Z∼10 −5 and a "top-heavy" IMF.…”

Section: Muse Spectroscopymentioning

confidence: 99%

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Stars and gas in the most metal-poor galaxies – I. COS and MUSE observations of SBS 0335−052E

Wofford

Vidal-García

Feltre

et al. 2020

Monthly Notices of the Royal Astronomical Society

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Among the nearest most metal-poor starburst-dwarf galaxies known, SBS 0335-052E is the most luminous in integrated nebular He ii λ4686 emission. This makes it a unique target to test spectral synthesis models and spectral interpretation tools of the kind that will be used to interpret future rest-frame UV observations of primeval galaxies. Previous attempts to reproduce its He ii λ4686 luminosity found that X-ray sources, shocks, and single Wolf-Rayet stars are not main contributors to the He ii-ionizing budget; and that only metal-free single rotating stars or binary stars with a top-heavy IMF and an unphysically-low metallicity can reproduce it. We present new UV (COS) and optical (MUSE) spectra which integrate the light of four super star clusters in SBS 0335-052E. Nebular He ii, [C iii], C iii], C iv, and O iii] UV emission lines with equivalent widths between 1.7 and 5 Å, and a C iv λλ1548, 1551 P-Cygni like profile are detected. Recent extremely-metal poor shock + precursor models and binary models fail to reproduce the observed optical emission-line ratios. We use different sets of UV and optical observables to test models of constant star formation with single non-rotating stars which account for very massive stars, as blueshifted O v λ1371 absorption is present. Simultaneously fitting the fluxes of all high-ionization UV lines requires an unphysically-low metallicity. Fitting the P-Cygni like + nebular components of C iv λλ1548, 1551 does not constrain the stellar metallicity and time since the beginning of star formation. We obtain 12+log(O/H) = 7.45 ± 0.04 and log(C/O)$\, =-0.45^{+0.03}_{-0.04}$ for the galaxy. Model-testing would benefit from higher spatial resolution UV and optical spectroscopy of the galaxy.

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Section: Introductionmentioning

confidence: 91%

Section: Muse Spectroscopymentioning

confidence: 99%

Stars and gas in the most metal-poor galaxies – I. COS and MUSE observations of SBS 0335−052E

Wofford

Vidal-García

Feltre

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…Previous observations have revealed that many low-metallicity star-forming galaxies produce these hard photons much more efficiently than predicted by stellar population synthesis models (e.g. Shirazi & Brinchmann 2012;Senchyna et al 2017;Berg et al 2018;Kehrig et al 2018) which suggests significant systematic uncertainties may arise in the interpretation of He ii emission at high redshift. In particular, we found in S17 that the relative flux beyond the He + -ionizing edge is strongly dependent on metallicity, and suggests a dramatic upturn in the hardness of this ionizing radiation at low metallicities.…”

Section: He II Emission In the Xmp Regimementioning

confidence: 99%

Extremely metal-poor galaxies with HST/COS: laboratories for models of low-metallicity massive stars and high-redshift galaxies

Senchyna

Stark

Chevallard

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Abstract 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 ($\rm W_{C\, {\scriptscriptstyle IV},0}{} \gtrsim 20$ Å) are uniformly stronger than observed locally ($\rm W_{C\, {\scriptscriptstyle IV},0}{} \lesssim 2$ Å), likely due to the relatively high metallicities (Z/Z$\odot$ > 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$\odot$ ≲ 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$\odot$ < 0.1) massive stars in assembling reionization-era systems.

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“…All line fluxes in Figs 6 and 7 are corrected for attenuation by dust, as prescribed in the original studies. We note that the line ratios in these figures are subject to uncertainties linked to the different apertures used to observe different galaxy samples, as highand low-ionization lines are not necessarily co-spatial (see, e.g., Kehrig et al 2018).…”

Section: Global Observational Properties Of the Full Samplementioning

confidence: 99%

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

Plat

Charlot

Bruzual³

et al. 2019

Monthly Notices of the Royal Astronomical Society

112

133

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We explore the production and escape of ionizing photons in young galaxies by investigating the ultraviolet and optical emission-line properties of models of ionizationbounded and density-bounded H regions, active-galactic-nucleus (AGN) narrow-line regions and radiative shocks computed all using the same physically-consistent description of element abundances and depletion on to dust grains down to very low metallicities. We compare these models with a reference sample of metal-poor star-forming galaxies and Lyman-continuum (LyC) leakers at various redshifts, which allows the simultaneous exploration of more spectral diagnostics than typically available at once for individual subsamples. We confirm that current single-and binary-star population synthesis models do not produce hard-enough radiation to account for the high-ionization emission of the most metal-poor galaxies. Introducing either an AGN or radiative-shock component brings models into agreement with observations. A published model including X-ray binaries is an attractive alternative to reproduce the observed rise in He λ4686/Hβ ratio with decreasing oxygen abundance in metal-poor star-forming galaxies, but not the high observed He λ4686/Hβ ratios of galaxies with large EW(Hβ). A source of harder ionizing radiation appears to be required in these extreme objects, such as an AGN or radiative-shock component, perhaps linked to an initial-mass-function bias toward massive stars at low metallicity. This would also account for the surprisingly high [O ]/[O ] ratios of confirmed LyC leakers relative to ionization-bounded models. We find no simple by-eye diagnostic of the nature of ionizing sources and the escape of LyC photon, which require proper simultaneous fits of several lines to be discriminated against. galactic nuclei (AGN), arising from gas accretion onto primordial black holes; radiative shocks, induced by large-scale gas flows; and the leakage of Lyman-continuum (LyC) photons through a porous interstellar medium (ISM), contributing to reionization (see, e.g., the review by Stark 2016). In waiting for advent of the James Webb Space Telescope (JWST), which will enable deep rest-frame ultraviolet and optical emission-line spectroscopy of galaxies into the reionization era at redshifts z ∼ 10-15, more nearby metal-poor galaxies approaching the properties of primeval galaxies offer a useful laboratory in which to test our ability to interpret emission-line spectra.

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The extended HeIIλ4686 emission in the extremely metal-poor galaxy SBS 0335-052E seen with MUSE★

Cited by 57 publications

References 108 publications

Stars and gas in the most metal-poor galaxies – I. COS and MUSE observations of SBS 0335−052E

Stars and gas in the most metal-poor galaxies – I. COS and MUSE observations of SBS 0335−052E

Extremely metal-poor galaxies with HST/COS: laboratories for models of low-metallicity massive stars and high-redshift galaxies

Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies

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