Ultraviolet spectra of extreme nearby star-forming regions: Evidence for an overabundance of very massive stars

Senchyna, Peter; Stark, Daniel P.; Charlot, S.; Chevallard, Jacopo; Bruzual, G.; Vidal-García, Alba

doi:10.1093/mnras/stab884

Cited by 38 publications

(58 citation statements)

References 140 publications

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“…The effects of binary star evolution have been proposed as a remedy to this issue, since they yield significant LyC production even after the most massive stars have exploded (e.g., Ma et al 2016;Rosdahl et al 2018;Doughty & Finlator 2021). The EWs of nebular He and C emission can help test this scenario since they are sensitive to hotter stars than HI-ionising stars, and may probe Myr timescales (e.g., Götberg et al 2019;Stanway et al 2020;Senchyna et al 2021). Knowledge of the origin of these strong nebular lines could in the future further help timing the LyC leaking phases.…”

Section: 4mentioning

confidence: 99%

“…However, latest stellar population models are unable to match the observed EWs of these lines (bottom panel of Figure 7), and so quantitative details relying on these models such as the exact time when He 𝜆1640 production peaks after a burst are uncertain. We now have yet another motivating reason -understanding LyC 𝑓 esc -to unravel the origins of nebular He (e.g., Stanway et al 2020;Senchyna et al 2021;Simmonds et al 2021;Olivier et al 2021).…”

Section: Caveats and Limitationsmentioning

confidence: 99%

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The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

Naidu

Matthee

Oesch

et al. 2021

Monthly Notices of the Royal Astronomical Society

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The ionizing photon escape fraction (LyC fesc) of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshifts. Here we circumvent this uncertainty by inferring fesc using resolved (R > 4000) Lyα profiles from the X-SHOOTER Lyα survey at z = 2 (XLS-z2). With empirically motivated criteria, we use Lyα profiles to select leakers (fesc$>20\%$) and non-leakers (fesc$<5\%$) from a representative sample of >0.2L* Lyman-α emitters (LAEs). We use median stacked spectra of these subsets over λrest ≈ 1000 − 8000Å to investigate the conditions for LyC fesc. Our stacks show similar mass, metallicity, MUV, and βUV. We find the following differences between leakers vs. non-leakers: (i) strong nebular CIV and HeII emission vs. non-detections, (ii) [O iii]/[O ii]≈8.5 vs. ≈3, (iii) Hα/Hβ indicating no dust vs. E(B − V) ≈ 0.3, (iv) MgII emission close to the systemic velocity vs. redshifted, optically thick MgII, (v) Lyα fesc of $\approx 50\%$ vs. $\approx 10\%$. The extreme EWs in leakers ([O iii]+Hβ ≈ 1100 Å rest-frame) constrain the characteristic timescale of LyC escape to ≈3 − 10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers – extremely ionizing stellar populations, low column densities, a dust-free, high ionization state ISM – occur simultaneously in the fesc$>20\%$ stack, suggesting they are causally connected, and motivating why indicators like [O iii]/[O ii] may suffice to constrain fesc at z > 6 with JWST. The leakers comprise half our sample, have a median LyC fesc$\approx 50\%$ (conservative range: $20-55\%$), and an ionising production efficiency $\log ({\xi _{\rm {ion}}/\rm {Hz\ erg^{-1}}})\approx 25.9$ (conservative range: 25.7 − 25.9). These results show LAEs – the type of galaxies rare at z ≈ 2, but that become the norm at higher redshift – are highly efficient ionizers, with extreme ξion and prolific fesc occurring in sync.

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Section: 4mentioning

confidence: 99%

Section: Caveats and Limitationsmentioning

confidence: 99%

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

Naidu

Matthee

Oesch

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…From gas phase abundance measurements based on rest-frame optical emission lines, it has been suggested that there is a deficiency of EW 0 (C iii) 10 Å objects at 12 + log 10 (O/H) 8.5 (Maseda et al 2017;Senchyna et al 2017). Senchyna et al (2021) argues that this deficiency might even be for objects at 12 + log 10 (O/H) 8.0 (Z/Z 0.2). In line with these findings the UV-based gas-phase abundances presented in Fig.…”

Section: Estimating Gas-phase Abundancesmentioning

confidence: 99%

“…By including the BPASS-based models we attempt to accommodate the influence and likely important effect binary stellar populations have on the amount and strength of the ionizing photons being produced by star formation. In particular, for high-ionization lines like C iv and He ii it has been argued that binary stellar populations are needed, though not always enough, to produce the observed emission from non-AGN galaxies (e.g., Steidel et al 2016Steidel et al , 2018Berg et al 2019a;Nanayakkara et al 2019;Senchyna et al 2021).…”

Section: Physical Parameter Inference From Photoionization Modelsmentioning

confidence: 99%

“…Determining the emission flux ratios of different UV line species and comparing them to grids of photoionization models predicting UV line fluxes provides estimates of, for instance, the metallicity and gas-phase abundances, the ionization parameter, and hydrogen number density (e.g., Gutkin et al 2016;Feltre et al 2016;Jaskot & Ravindranath 2016;Hirschmann et al 2017Hirschmann et al , 2019Byler et al 2017Byler et al , 2018Byler et al , 2020Nakajima et al 2018;Plat et al 2019;Kewley et al 2019a). The He ii λ1640 emission likely includes both nebular emission and emission from stellar winds (Byler et al 2018(Byler et al , 2020 and is therefore a valuable probe and diagnostic of these parameters, even though it has been proven challenging to reproduce the total observed He ii emission from star-forming galaxies without invoking increased ionizing photon production from binary stars and/or X-ray binaries (e.g., Steidel et al 2016Steidel et al , 2018Berg et al 2019a;Nanayakkara et al 2019;Senchyna et al 2021).…”

Section: Introductionmentioning

confidence: 99%

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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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The Driving of Hot Star Winds

Sander

2021

Proc. IAU

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In the regime of hot stars, winds were not seen as a common thing until the era of UV astronomy. Since we have access to the UV wavelength range, it has become clear that winds are not an exotic phenomenon limited to some special objects, but actually ubiquitous among hot and massive stars. The opacities due to spectral lines are the decisive ingredient that allows hot, massive stars to launch powerful winds. While the fundamental principles of these so-called line-driven winds have been realized decades ago, their proper quantitative prediction is still a major challenge today. Established theoretical and empirical descriptions have allowed us to make major progress on all astrophysical scales. However, we are now reaching their limitations as we still lack various fundamental insights on the nature of hot star winds, thereby hampering us from drawing deeper conclusions, not least when dealing with stellar or sub-stellar companions. This has spawned a new generation of researchers searching for answers with a yet unprecedented level of detail in observational and new theoretical approaches.In these proceedings, the fundamental principles of driving hot star winds will be briefly reviewed. Starting from the classical CAK theory and its extensions, over Monte Carlo and recent comoving-frame-based simulations, the different methods to describe and model the acceleration of hot star winds will be introduced. The review continues with briefly discussing instabilities as well as qualitative and quantitative insights for OB- and Wolf-Rayet-star winds. Moreover, the challenges of companions and their impact on radiation-driven winds are outlined.

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Ultraviolet spectra of extreme nearby star-forming regions: Evidence for an overabundance of very massive stars

Cited by 38 publications

References 140 publications

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

The synchrony of production and escape: half the bright Lyα emitters at z ≈ 2 have Lyman continuum escape fractions ≈50

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

The Driving of Hot Star Winds

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