The Evolution and Properties of Rotating Massive Star Populations

Choi, Jieun; Conroy, Charlie; Byler, Nell

doi:10.3847/1538-4357/aa679f

Cited by 82 publications

(85 citation statements)

References 148 publications

(228 reference statements)

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“…However, the massive stars exploding as supernovae are precisely the ones producing most of the ionizing photons. Invoking effects like binarity and rotation allow a significant population of UV luminous stars to survive longer and pump LyC through the newly cleared ISM (Choi et al 2017). The ionized channels visible in high-resolution Lyα spectra of LyC leakers (Vanzella et al 2019) support this picture.…”

Section: Motivation: Why σ Sfr ?mentioning

confidence: 99%

Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions

Naidu

Tacchella

Mason

et al. 2020

ApJ

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289

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The protagonists of the last great phase transition of the universe -cosmic reionization -remain elusive. Faint star-forming galaxies are leading candidates because they are found to be numerous and may have significant ionizing photon escape fractions (f esc ). Here we update this picture via an empirical model that successfully predicts latest observations (e.g., the rapid drop in star-formation density (ρ SFR ) at z > 8). We generate an ionizing spectrum for each galaxy in our model and constrain f esc by leveraging latest measurements of the reionization timeline (e.g., Lyα damping of quasars and galaxies at z > 7). Assuming a constant f esc across all sources at z > 6, we find M UV < −13.5 galaxies need f esc =0.21 +0.06 −0.04 to complete reionization. The inferred IGM neutral fraction is [0.9, 0.5, 0.1] at z = [8.2, 6.8, 6.2] ± 0.2, i.e., the bulk of reionization transpires rapidly in 300 Myrs, driven by the z > 8 ρ SFR and favored by high neutral fractions (∼60−90%) measured at z ∼ 7 − 8. Inspired by the emergent sample of Lyman Continuum (LyC) leakers spanning z ∼ 0−6.6 that overwhelmingly displays higher-than-average star-formation surface density (Σ SFR ), we propose a physically motivated model relating f esc to Σ SFR and find f esc ∝ Σ 0.4±0.1 SFR . Since Σ SFR falls by ∼ 2.5 dex between z = 8 and z = 0, our model explains the humble upper limits on f esc at lower redshifts and its required evolution to f esc ∼ 0.2 at z > 6. Within this model, strikingly, <5% of galaxies with M UV < −18 and log(M /M ) > 8 (the 'oligarchs') account for 80% of the reionization budget -a stark departure from the canonical 'democratic' reionization led by copious faint sources. In fact, faint sources (M UV >−16) must be relegated to a limited role in order to ensure high neutral fractions at z = 7 − 8. Shallow faint-end slopes of the UV luminosity function (α UV > −2) and/or f esc distributions skewed toward massive galaxies produce the required late and rapid reionization. We predict LyC leakers like COLA1 (z = 6.6, f esc ∼ 30%, M UV = −21.5) become increasingly common towards z ∼ 6 and that the drivers of reionization do not lie hidden across the faint-end of the luminosity function, but are already known to us.

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Section: Motivation: Why σ Sfr ?mentioning

confidence: 99%

Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions

Naidu

Tacchella

Mason

et al. 2020

ApJ

Self Cite

289

251

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“…The net result is hotter, brighter, and longer-lived (by between 5-20%) massive stars (Choi et al 2016). This in turn causes higher UV and ionizing photon production in stellar populations between 0-20 Myr (Choi et al 2017), especially at sub-solar metallicities. We note that models for rotation in stars are sensitive to implementation details and their predictions vary substantially; for example the Geneva rotation model (Ekström et al 2012) predicts both hotter and brighter stars than the MIST models adopted here ( Fig.…”

Section: Treatment Of Photometric Zero Pointsmentioning

confidence: 99%

“…Large uncertainties in the IR contribution of TP-AGB stars have largely been resolved (Maraston et al 2006;Kriek et al 2010), though other fundamental uncertainties in stellar population synthesis techniques remain (e.g. the effect of binaries and rotation on the ionizing flux production rates of massive stars, Choi et al 2017).…”

Section: Introductionmentioning

confidence: 99%

An Older, More Quiescent Universe from Panchromatic SED Fitting of the 3D-HST Survey

Leja

Johnson

Conroy

et al. 2019

ApJ

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243

298

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Galaxy observations are influenced by many physical parameters: stellar masses, star formation rates (SFRs), star formation histories (SFHs), metallicities, dust, black hole activity, and more. As a result, inferring accurate physical parameters requires high-dimensional models which capture or marginalize over this complexity. Here we re-assess inferences of galaxy stellar masses and SFRs using the 14-parameter physical model Prospector-α built in the Prospector Bayesian inference framework. We fit the photometry of 58,461 galaxies from the 3D-HST catalogs at 0.5 < z < 2.5. The resulting stellar masses are ∼ 0.1 − 0.3 dex larger than the fiducial masses while remaining consistent with dynamical constraints. This change is primarily due to the systematically older SFHs inferred with Prospector. The SFRs are ∼ 0.1 − 1+ dex lower than UV+IR SFRs, with the largest offsets caused by emission from "old" (t > 100 Myr) stars. These new inferences lower the observed cosmic star formation rate density by ∼ 0.2 dex and increase the observed stellar mass growth by ∼ 0.1 dex, finally bringing these two quantities into agreement and implying an older, more quiescent Universe than found by previous studies at these redshifts. We corroborate these results by showing that the Prospector-α SFHs are both more physically realistic and are much better predictors of the evolution of the stellar mass function. Finally, we highlight examples of observational data which can break degeneracies in the current model; these observations can be incorporated into priors in future models to produce new & more accurate physical parameters.

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“…Narrow He II emission is generally interpreted as having a nebular origin, and requires significant numbers of high energy photons. With currently available stellar models, very hard ionizing spectra requires the presence of stellar multiplicity, stellar rotation, or very massive stars (e.g., Stark et al 2014;Steidel et al 2016;Byler et al 2017;Choi et al 2017).…”

Section: He II λ1640mentioning

confidence: 99%

A Comparison of UV and Optical Metallicities in Star-forming Galaxies

Byler

Kewley

Rigby

et al. 2020

ApJ

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Our ability to study the properties of the interstellar medium (ISM) in the earliest galaxies will rely on emission line diagnostics at rest-frame ultraviolet (UV) wavelengths. In this work, we identify metallicity-sensitive diagnostics using UV emission lines. We compare UV-derived metallicities with standard, well-established optical metallicities using a sample of galaxies with rest-frame UV and optical spectroscopy. We find that the He2-O3C3 diagnostic (He II λ1640Å / C III] λ1906,1909Å vs. [O III] λ1666Å / C III] λ1906,9Å) is a reliable metallicity tracer, particularly at low metallicity (12 + log 10 (O/H) ≤ 8), where stellar contributions are minimal. We find that the Si3-O3C3 diagnostic ([Si III] λ1883Å / C III] λ1906Å vs. [O III] λ1666Å / C III] λ1906,9Å) is a reliable metallicity tracer, though with large scatter (0.2-0.3 dex), which we suggest is driven by variations in gas-phase abundances. We find that the C4-O3C3 diagnostic (C IV λ 1548,50Å / [O III] λ 1666Å vs. [O III] λ 1666Å / C III] λ 1906,9Å) correlates poorly with optically-derived metallicities. We discuss possible explanations for these discrepant metallicity determinations, including the hardness of the ionizing spectrum, contribution from stellar wind emission, and non-solar-scaled gas-phase abundances. Finally, we provide two new UV oxygen abundance diagnostics, calculated from polynomial fits to the model grid surface in the He2-O3C3 and Si3-O3C3 diagrams.

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The Evolution and Properties of Rotating Massive Star Populations

Cited by 82 publications

References 148 publications

Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions

Rapid Reionization by the Oligarchs: The Case for Massive, UV-bright, Star-forming Galaxies with High Escape Fractions

An Older, More Quiescent Universe from Panchromatic SED Fitting of the 3D-HST Survey

A Comparison of UV and Optical Metallicities in Star-forming Galaxies

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