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

Wofford, Aida; Vidal-García, Alba; Feltre, Anna; Chevallard, Jacopo; Charlot, S.; Stark, Daniel P.; Herenz, Edmund Christian; Hayes, Matthew

doi:10.1093/mnras/staa3365

Cited by 28 publications

(31 citation statements)

References 141 publications

(230 reference statements)

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“…This problem is often seen for He II observations (e.g. Kehrig et al 2015Kehrig et al , 2018Kehrig et al , 2021Senchyna et al 2017Senchyna et al , 2020Wofford et al 2021), but we emphasize that the discrepancy between photoionization models using the stellar continuum as the input ionizing spectra and observations of emission lines is a problem for all very-high ionization lines, especially He II and [O IV], as seen in §4.2.1 and §4.2.2 above. Here we explore what is required to reconcile the observed nebular emission lines with the models.…”

Section: Combination Stellar + Blackbody Modelsmentioning

confidence: 76%

“…Another option to produce our BB radiation is very massive stars, stars that are >100M , which could be more plausible in the low metallicity regime. Very massive stars have been detected in SBS0335-052E by Wofford et al (2021) who claim the models of very massive stars reproduce the UV and optical emission lines they have observed. Additionally, Senchyna et al (2020) used a sample of 10 star-forming galaxies from the Sloan Digital Sky Survey to conclude that the discrepancy between stellar population models and the observed UV lines could only be rectified with additional very massive stars.…”

Section: What Is the Source Of The High Energy Photons?mentioning

confidence: 99%

“…A number of studies have explored the production mechanism for the extreme He II emission at λ1640 in the restframe UV and λ4686 in the optical in a number of these reionization analogues (e.g., Schaerer 2002;Kehrig et al 2015Kehrig et al , 2018Kehrig et al , 2021Schaerer et al 2019;Senchyna et al 2017Senchyna et al , 2020. Some of the postulated sources of the He II emission include: Wolf-Rayet stars at low metallicity, high-mass X-ray binaries, metal-poor massive stars, and shocks, but, when examined in more detail, these suggestions tend to be inadequate in their photon production in the energy range needed for extreme He II emission (Kehrig et al 2015(Kehrig et al , 2018Senchyna et al 2020;Wofford et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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Characterizing Extreme Emission Line Galaxies II: A Self-Consistent Model of Their Ionizing Spectrum

Olivier¹,

Berg²,

Chisholm³

et al. 2021

Preprint

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Observations of high-redshift galaxies (z > 5) have shown that these galaxies have extreme emission lines with equivalent widths much larger than their local star-forming counterparts. Extreme emission line galaxies (EELGs) in the nearby universe are likely analogues to galaxies during the Epoch of Reionization and provide nearby laboratories to understand the physical processes important to the early universe. We use HST/COS and LBT/MODS spectra to study two nearby EELGs, J104457 and J141851. The FUV spectra indicate that these two galaxies contain stellar populations with ages < ∼ 10 Myr and metallicities ≤0.15 Z . We use photoionization modeling to compare emission lines from models of single-age bursts of star-formation to observed emission lines and find that the single-age bursts do not reproduce high-ionization lines including [O III] or very-high ionization lines like He II or [O IV]. Photoionization modeling using the stellar populations fit from the UV continuum similarly are not capable of reproducing the emission lines from the very-high ionization zone. We add a blackbody to the stellar populations fit from the UV continuum to model the necessary highenergy photons to reproduce the very-high ionization lines of He II and [O IV]. We find that we need a blackbody of 80,000 K and ∼60-70% of the luminosity from the young stellar population to reproduce the very-high ionization lines while simultaneously reproducing the low-, intermediate-, and high-ionization emission lines. Our self-consistent model of the ionizing spectra of two nearby EELGs indicates the presence of a previously unaccounted-for source of hard ionizing photons in reionization analogues.

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Section: Combination Stellar + Blackbody Modelsmentioning

confidence: 76%

Section: What Is the Source Of The High Energy Photons?mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Characterizing Extreme Emission Line Galaxies II: A Self-Consistent Model of Their Ionizing Spectrum

Olivier¹,

Berg²,

Chisholm³

et al. 2021

Preprint

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“…In order to address this caveat in the future, new detailed observations of very distant galaxies will need to be accompanied by observations of local analogous galaxies (e.g. Kehrig et al 2015;Wofford et al 2021) and Hii regions in the (very) nearby Universe (e.g. Castro et al 2018) that can allow the detailed resolved observations required to constrain models describing the properties of massive stars at very low metallicities in detail.…”

Section: Caveatsmentioning

confidence: 99%

“…Fosbury et al 2003;Erb et al 2010;Steidel et al 2016;Berg et al 2018;Nanayakkara et al 2019;Saxena et al 2020;Matthee et al 2021) and in their local analogues (e.g. Kehrig et al 2015;Wofford et al 2021). In practically all cases these Heii lines appear together with strong emission from high ionisation metal lines as Civ and Oiii].…”

Section: Introductionmentioning

confidence: 97%

Deciphering stellar metallicities in the early Universe: Case study of a young galaxy at z = 4.77 in the MUSE eXtremely Deep Field

Matthee,

Feltre,

Maseda

et al. 2021

Preprint

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Directly characterising the first generations of stars in distant galaxies is a key quest of observational cosmology. Here, we present a case study of ID53 at z = 4.77, the UV-brightest (yet L ) star-forming galaxy at z > 3 in the MUSE eXtremely Deep Field with a mass of ≈ 10 9 M . Besides very strong Lyman-α (Lyα) emission, we clearly detect the (stellar) continuum and a NV P-Cygni feature, interstellar absorption, fine-structure emission and nebular CIV emission-lines in the 140 hr spectrum. Continuum emission from two spatially resolved components in the HST data are blended in the MUSE data, but we show that the nebular CIV emission originates from a subcomponent of the galaxy. The UV spectrum can be fit with recent BPASS stellar population models combined with single burst or continuous star formation histories (SFHs), a standard initial mass function and attenuation law. Models with a young age and low metallicity (log 10 (age/yr)=6.5-7.6 and [Z/H]=-2.15 to -1.15) are preferred, but the details depend on the assumed SFH. The intrinsic Hα luminosity of the best-fit models is an order of magnitude higher than the Hα luminosity inferred from Spitzer/IRAC data, which either suggests a high escape fraction of ionising photons, a high relative nebular to stellar dust attenuation or a complex star formation history. The metallicity appears lower than the metallicity in more massive galaxies at z = 3 − 5, consistent with the picture in which younger galaxies have lower metallicities. Such chemical immaturity likely facilitates Lyα escape, explaining why the Lyα equivalent width anti-correlates with stellar metallicity. Finally, we stress that uncertainties in SFHs impose a challenge for future inferences of the stellar metallicity of young galaxies. This highlights the need for joint (spatially resolved) analyses of stellar spectra and photo-ionisation models.

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Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at 1.5 <z< 6.4

Schmidt

Kerutt

Wisotzki

et al. 2021

A&A

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Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Lyα, has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Lyα emission becomes increasingly challenging at z ≳ 6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxies’ physical properties and their Lyα emission. The sample of 2052 emission line sources with 1.5 < z < 6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic campaigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Lyα) UV emission lines increases with survey depth, and that the emission line strength of He IIλ1640 Å, [O III] λ1661 + O III] λ1666, and [Si III] λ1883 + Si III] λ1892 correlate with the strength of [C III] λ1907 + C III] λ1909. The rest-frame equivalent width (EW0) of [C III] λ1907 + C III] λ1909 is found to be roughly 0.22 ± 0.18 of EW0(Lyα). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For C IVλ1548 + C IVλ1551 we find that ΔvC IV ≲ 250 km s−1, whereas ΔvLyα falls in the range of 250−500 km s−1 which is in agreement with previous results from the literature. The electron density ne measured from [Si III] λ1883 + Si III] λ1892 and [C III] λ1907 + C III] λ1909 line flux ratios is generally < 105 cm−3 and the gas-phase abundance is below solar at 12 + log10(O/H)≈8. Lastly, we used “PhotoIonization Model Probability Density Functions” to infer physical parameters of the full sample and individual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log10(U) ≈ −2.5 and metal mass fractions that scatter around Z ≈ 10−2, that is Z ≈ 0.66 Z⊙. Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper.

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

Cited by 28 publications

References 141 publications

Characterizing Extreme Emission Line Galaxies II: A Self-Consistent Model of Their Ionizing Spectrum

Characterizing Extreme Emission Line Galaxies II: A Self-Consistent Model of Their Ionizing Spectrum

Deciphering stellar metallicities in the early Universe: Case study of a young galaxy at z = 4.77 in the MUSE eXtremely Deep Field

Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at 1.5 <z< 6.4

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