Massive Star Formation in the Ultraviolet Observed with the Hubble Space Telescope

Leitherer, Claus

doi:10.3390/galaxies8010013

Cited by 12 publications

(5 citation statements)

References 102 publications

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“…We also do not detect any other rest-frame UV metal lines (e.g. O iii]λλ1661,1666, N iv]λλ1483,1487, N vλ1240), inconsistent with the signatures of Wolf-Rayet and stripped stars that are frequently seen in local galaxies 31,32 .…”

contrasting

confidence: 77%

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

Wang

Cheng

Ge³

et al. 2022

Preprint

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Cosmic hydrogen reionization and cosmic production of first metals are major phase transitions of the Universe occurring during the first billion years after the Big Bang, but still poorly explored observationally. Using the JWST NIRSpec prism spectroscopy, we report the discovery of a sub-L* galaxy at zspec = 8.1623-0.0008+0.0007, dubbed RXJ2129-z8HeII, via the detection of a series of strong rest-frame UV/optical nebular emission lines and the clear Lyman break. A strong He II λ1640 emission is present, the highest redshift He II line currently known. Its high rest-frame equivalent width (EW=19.38 ± 3.24 Å) and extreme flux ratios with respect to UV metal lines and Balmer lines raise the possibility that part of RXJ2129-z8HeII's stellar populations could be Pop III-like5,6. RXJ2129-z8HeII also shows a pronounced UV continuum with an extremely steep (i.e. blue) spectral slope of β =-2.50±0.08, the steepest amongst all spectroscopically confirmed galaxies at z ≳ 7, in support of its very hard ionizing spectrum that could lead to a significant leakage of its ionizing flux7. Therefore, RXJ2129-z8HeII is representative of the key galaxy population driving the cosmic reionization. To date, this is also the most compelling case where trace Pop III stars might coexist with more metal-enriched stars.

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contrasting

confidence: 77%

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

Wang

Cheng

Ge³

et al. 2022

Preprint

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“…However, their He II EWs are reported to be less than 10 Å, not as high as that measured in our galaxy, and their He II emission is likely caused by stellar binarity and density-bounded H II regions with subsolar ISM metallicities (Plat et al 2019). We do not detect any UV metal lines (e.g., C III], C IV, O III], N IV] λλ1483, 1487, N V λ1240) either, inconsistent with the signatures of W-R and stripped stars that are often seen in local galaxies (Morris et al 2008;Leitherer 2020), although we caution that the strength of these wind lines for W-R and stripped stars is metallicity-dependent and is likely to be very weak at extremely low metallicities (e.g., much lower than onetenth solar).…”

contrasting

confidence: 66%

A Strong He ii λ1640 Emitter with an Extremely Blue UV Spectral Slope at z = 8.16: Presence of Population III Stars?

Wang,

Cheng,

et al. 2024

ApJL

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Cosmic hydrogen reionization and cosmic production of the first metals are major phase transitions of the Universe occurring during the first billion years after the Big Bang; however, these are still underexplored observationally. Using the JWST/NIRSpec prism spectroscopy, we report the discovery of a sub-L * galaxy at z spec = 8.1623 ± 0.0007, dubbed RX J2129–z8He II, via the detection of a series of strong rest-frame UV/optical nebular emission lines and the clear Lyman break. RX J2129–z8He II shows a pronounced UV continuum with an extremely steep (i.e., blue) spectral slope of β = − 2.53 − 0.07 + 0.06 , the steepest among all spectroscopically confirmed galaxies at z spec ≳ 7, in support of its very hard ionizing spectrum that could lead to a significant leakage of its ionizing flux. Therefore, RX J2129–z8He II is representative of the key galaxy population driving the cosmic reionization. More importantly, we detect a strong He II λ1640 emission line in its spectrum, one of the highest redshifts at which such a line is robustly detected. Its high rest-frame equivalent width (EW = 21 ± 4 Å) and extreme flux ratios with respect to UV metal and Balmer lines raise the possibility that part of RX J2129–z8He II’s stellar population could be Pop III (Pop III)-like. Through careful photoionization modeling, we show that the physically calibrated phenomenological models of the ionizing spectra of Pop III stars with strong mass loss can successfully reproduce the emission line flux ratios observed in RX J2129–z8He II. Assuming the Eddington limit, the total mass of the Pop III stars within this system is estimated to be 7.8 ± 1.4 × 105 M ⊙. To date, this galaxy presents the most compelling case in the early Universe where trace Pop III stars might coexist with metal-enriched populations.

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“…One of them involves the suggestion of stellar emission from VMS at low Z due to a strong but slow wind (see Figure 4). Gräfener & Vink [39] estimated the expected He II line flux and equivalent widths (EWs) based on their VMS wind models and Starburst99 [40,41] population synthesis models, and compared their results with observed star-forming galaxy spectra, finding that the measured He II line strengths and EWs are in line with what is expected for a VMS population in one or more young clusters located in these galaxies. Future high spectral resolution studies could help distinguish between nebular and stellar emission from VMS, taking into account that slower VMS winds yield narrower lines, possibly even below the slow-wind predictions from Gräfener & Vink [39].…”

Section: He II Emission At High Redshiftmentioning

confidence: 94%

Star Formation in the Ultraviolet

Vink

2020

Galaxies

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With the launch of JWST and the upcoming installation of extremely large telescopes, the first galaxies in our Universe will finally be revealed. Their light will be dominated by massive stars, which peak in in the ultra-violet (UV) part of the electromagnetic spectrum. Star formation is the key driver of the evolution of our Universe. At young ages, within 10 Million years, both high and low mass stars generate complex UV emission processes which are poorly understood yet are vital for interpreting high red-shift line emission. For these reasons, the Hubble Space Telescope (HST) will devote 1000 orbits to obtaining a UV Legacy Library of Young Stars as Essential Standards (ULLYSES). The purpose of this Overview is to outline the basic physical principles driving UV emission processes from local (within 100 parsecs of) star formation, ranging from huge star-forming complexes containing hundreds of massive and very-massive stars (VMS), such as 30 Doradus (the Tarantula Nebula) in the neighboring Magellanic Clouds (only 50 kpc away), to galaxies near and far, out to the epoch of Cosmic Reionization.

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Massive Star Formation in the Ultraviolet Observed with the Hubble Space Telescope

Cited by 12 publications

References 102 publications

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

A strong He II λ1640 emitter with extremely blue UV spectral slope at z=8.16: presence of Pop III stars?

A Strong He ii λ1640 Emitter with an Extremely Blue UV Spectral Slope at z = 8.16: Presence of Population III Stars?

Star Formation in the Ultraviolet

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