Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Leitherer, Claus; Byler, Nell; Lee, Janice; Levesque, Emily M.

doi:10.3847/1538-4357/aada84

Cited by 34 publications

(33 citation statements)

References 147 publications

(181 reference statements)

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“…The ultraviolet emission of the LyC−knot resembles those of local super star clusters in which the signatures of massive stars are clearly imprinted in the spectrum, like the prominent P-Cygni profiles of the Civλ1548, 1550 doublet and a broad Heiiλ1640 ascribed to the presence of Wolf-Rayet stars. The similarity with the ultraviolet spectra of a few well studied local young massive clusters is remarkable, namely R136 , II Z40 (Leitherer et al 2018) and cluster #5 of NG5253 (Smith et al 2016, see also Calzetti et al 2015), as well as the analogy with the nearby star forming regions collected by Senchyna et al (2017Senchyna et al ( , 2019 and showing high ionisation metal lines and in some cases broad Heiiλ1640 emission of low metallicity massive stars. The same spectral features, though at slightly lower S/N ratios, have been identified and accurately modelled by Chisholm et al (2019), providing a stellar age of 3.0 ± 0.1 Myr and subsolar stellar metallicity Z = 0.60 ± 0.05 Z , with an inferred dust extinction E(B-V) 0.15.…”

Section: The Sunburst Arcmentioning

confidence: 65%

Ionizing the intergalactic medium by star clusters: the first empirical evidence

Vanzella¹,

Caminha

Calura³

et al. 2019

Monthly Notices of the Royal Astronomical Society

123

124

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We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting galaxy Ion2 at z=3.2121 and compare it to that of the recently discovered strongly lensed LyC−emitter at z=2.37, known as the Sunburst arc. Three main results emerge from the X-Shooter spectrum: (a) the Lyα has three distinct peaks with the central one at the systemic redshift, indicating a ionised tunnel through which both Lyα and LyC radiation escape; (b) the large O32 oxygen index ([O iii]λλ4959, 5007 / [Oii]λ3727, 3729) of 9.18 +1.82 −1.32 is compatible to those measured in local (z ∼ 0.4) LyC leakers; (c) there are narrow nebular high-ionisation metal lines with σ v < 20 km s −1 , which confirms the presence of young hot, massive stars. The Heiiλ1640 appears broad, consistent with a young stellar component including Wolf−Rayet stars. Similarly, the Sunburst LyC−emitter shows a triple−peaked Lyα profile and from VLT/MUSE spectroscopy the presence of spectral features arising from young hot and massive stars. The strong lensing magnification, (µ > 20), suggests that this exceptional object is a gravitationally−bound star cluster observed at a cosmological distance, with a stellar mass M 10 7 M and an effective radius smaller than 20 pc. Intriguingly, sources like Sunburst but without lensing magnification might appear as Ion2−like galaxies, in which unresolved massive star clusters dominate the ultraviolet emission. This work supports the idea that dense young star clusters can contribute to the ionisation of the IGM through holes created by stellar feedback.

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Section: The Sunburst Arcmentioning

confidence: 65%

Ionizing the intergalactic medium by star clusters: the first empirical evidence

Vanzella¹,

Caminha

Calura³

et al. 2019

Monthly Notices of the Royal Astronomical Society

123

124

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“…We do not expect that stripped stars contribute significantly to the ionizing emission from populations with very high measured values for the ionization parameter of log 10 U −2 as observed by, for example, Erb et al (2010) and Leitherer et al (2018). When stripped stars dominate the ionizing emission, such high ionization parameters require that the galaxy is of high mass ( 10 8 M ) and that star formation has halted about 10 Myr ago (see Fig.…”

Section: Ionization Parameter Umentioning

confidence: 84%

The impact of stars stripped in binaries on the integrated spectra of stellar populations

Götberg

Mink

Groh

et al. 2019

A&A

103

120

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Stars stripped of their envelopes from interaction with a binary companion emit a significant fraction of their radiation as ionizing photons. They are potentially important stellar sources of ionizing radiation, however, they are still often neglected in spectral synthesis simulations or simulations of stellar feedback. In anticipating the large datasets of galaxy spectra from the upcoming James Webb Space Telescope, we modeled the radiative contribution from stripped stars by using detailed evolutionary and spectral models. We estimated their impact on the integrated spectra and specifically on the emission rates of H i-, He i-, and He ii-ionizing photons from stellar populations. We find that stripped stars have the largest impact on the ionizing spectrum of a population in which star formation halted several Myr ago. In such stellar populations, stripped stars dominate the emission of ionizing photons, mimicking a younger stellar population in which massive stars are still present. Our models also suggest that stripped stars have harder ionizing spectra than massive stars. The additional ionizing radiation, with which stripped stars contribute affects observable properties that are related to the emission of ionizing photons from stellar populations. In co-eval stellar populations, the ionizing radiation from stripped stars increases the ionization parameter and the production efficiency of hydrogen ionizing photons. They also cause high values for these parameters for about ten times longer than what is predicted for massive stars. The effect on properties related to non-ionizing wavelengths is less pronounced, such as on the ultraviolet continuum slope or stellar contribution to emission lines. However, the hard ionizing radiation from stripped stars likely introduces a characteristic ionization structure of the nebula, which leads to the emission of highly ionized elements such as O 2+ and C 3+ . We, therefore, expect that the presence of stripped stars affects the location in the BPT diagram and the diagnostic ratio of O iii to O ii nebular emission lines. Our models are publicly available through CDS database and on the Starburst99 website.

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“…The STARBURST99 stellar models were created using the WM-BASIC method (Pauldrach et al 2001) and densely sample the high-mass portion of the Hertzsprung-Russell diagram up to temperatures of 20,000 K. WM-BASIC does not calculate high-resolution models below these temperatures . Consequently, we chose the 10 stellar ages between 1 and 40 Myr listed above with stellar temperatures greater than 20,000 K. These models include Wolf-Rayet (WR) stars using the Potsdam Wolf-Rayet code (PoWR; Sander et al 2015), but the evolutionary tracks predict that few if any WR stars are present in a low-metallicity stellar population, such that the WR spectra are rarely incorporated into 0.2-0.4 Z e STARBURST99 models (Leitherer et al 2018).…”

Section: The Fiducial Case: Starburst99 Single-star Modelsmentioning

confidence: 99%

“…The BPASS models fit the He II region substantially better than the STARBURST99 models do, although they still do not match the WR features of younger populations. While both stellar models include WR models, neither model appears to produce a sufficient number of WR stars to match the broad He II emission observed in the youngest stellar populations (e.g., Leitherer et al 2018).…”

Section: The He II Emission Featurementioning

confidence: 99%

Constraining the Metallicities, Ages, Star Formation Histories, and Ionizing Continua of Extragalactic Massive Star Populations^∗

Chisholm

Rigby

Bayliss

et al. 2019

ApJ

139

167

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We infer the properties of massive star populations using the far-ultraviolet stellar continua of 61 star-forming galaxies: 42 at low redshift observed with the Hubble Space Telescope and 19 at z∼2 from the MEGaSaURA sample. We fit each stellar continuum with a linear combination of up to 50 single-age and single-metallicity STARBURST99 models. From these fits, we derive light-weighted ages and metallicities, which agree with stellar wind and photospheric spectral features, and infer the spectral shapes and strengths of the ionizing continua. Inferred light-weighted stellar metallicities span 0.05-1.5 Z e and are similar to the measured nebular metallicities. We quantify the ionizing continua using the ratio of the ionizing flux at 900 Å to the non-ionizing flux at 1500 Å and demonstrate the evolution of this ratio with stellar age and metallicity using theoretical single-burst models. These single-burst models only match the inferred ionizing continua of half of the sample, while the other half are described by a mixture of stellar ages. Mixed-age populations produce stronger and harder ionizing spectra than continuous star formation histories, but, contrary to previous studies that assume constant star formation, have similar stellar and nebular metallicities. Stellar population age and metallicity affect the far-UV continua in different and distinguishable ways; assuming a constant star formation history diminishes the diagnostic power. Finally, we provide simple prescriptions to determine the ionizing photon production efficiency (ξ ion ) from the stellar population properties. The ξ ion inferred from the observed star-forming galaxies has a range of log(ξ ion )=24.4-25.7 Hz erg −1 that depends on the stellar population age, metallicity, star formation history, and contributions from binary star evolution. These stellar population properties must be observationally determined to accurately determine the number of ionizing photons generated by massive stars.

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Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Cited by 34 publications

References 147 publications

Ionizing the intergalactic medium by star clusters: the first empirical evidence

Ionizing the intergalactic medium by star clusters: the first empirical evidence

The impact of stars stripped in binaries on the integrated spectra of stellar populations

Constraining the Metallicities, Ages, Star Formation Histories, and Ionizing Continua of Extragalactic Massive Star Populations^∗

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Physical Properties of II Zw 40's Super Star Cluster and Nebula: New Insights and Puzzles from UV Spectroscopy

Cited by 34 publications

References 147 publications

Ionizing the intergalactic medium by star clusters: the first empirical evidence

Ionizing the intergalactic medium by star clusters: the first empirical evidence

The impact of stars stripped in binaries on the integrated spectra of stellar populations

Constraining the Metallicities, Ages, Star Formation Histories, and Ionizing Continua of Extragalactic Massive Star Populations∗

Contact Info

Product

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Constraining the Metallicities, Ages, Star Formation Histories, and Ionizing Continua of Extragalactic Massive Star Populations^∗