On the detection of supermassive primordial stars – II. Blue supergiants

Surace, Marco; Zackrisson, Erik; Whalen, Daniel J.; Hartwig, Tilman; Glover, Simon C. O.; Woods, Tyrone E.; Heger, Alexander

doi:10.1093/mnras/stz1956

Cited by 27 publications

(22 citation statements)

References 91 publications

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“…Although a detailed comparison is clearly beyond the scope of this paper, we note that the predicted magnitudes of our models A4 are comparable to those of the cool SMS of Surace et al (2018), which reach ∼ 28 − 31 mag (AB) at z ∼ 6 − 10 in photometric bands in common with our work. As expected, the more compact bluer primordial SMS are fainter in the same filters, and are accordingly more difficult to detect, according to Surace et al (2019). Their spectral shape should also be less distinct from that of a normal stellar cluster, and they are therefore expected to be more difficult to identify if present, even in isolation, that is, without a surrounding young cluster population as considered here.…”

Section: Comparison With Other Resultssupporting

confidence: 54%

Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift

Martins

Haemmerlé

Charbonnel

2019

A&A

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Context. Globular clusters (GCs) contain multiple stellar populations with peculiar chemical compositions. Pollution of the intracluster gas by an early population of fast-evolving stars is the most common scenario for explaining the observations. Stars with masses in excess of 1000 M have recently been suggested as potential polluters. Aims. We investigate the spectral properties of proto-GCs that would host a supermassive star (SMS). Our main goal is to quantify how such a star would affect the integrated light of the cluster, and to study the detectability of such objects. Methods. We computed nonlocal thermal equilibirum atmosphere models for SMS with various combinations of stellar parameters (luminosity, effective temperature, and mass) and metallicities appropriate for GCs, and we predict their emergent spectra. Using these spectra, we calculated the total emission of young proto-GCs with SMS as predicted in a previously reported scenario, and we computed synthetic photometry in UV, optical, and near-IR bands, in particular for the James Webb Space Telescope (JWST).Results. At an effective temperature of 10000 K, the spectrum of SMSs shows a Balmer break in emission. This feature is due to strong nonlocal thermal equilibrium effects (implied by the high luminosity) and is not observed in "normal" stars. The hydrogen lines also show a peculiar behavior, with Balmer lines in emission while higher series lines are in absorption. At 7000 K, the Balmer break shows a strong absorption. At high effective temperatures, the Lyman break is found in emission. Cool and luminous SMSs are found to dominate the integrated spectrum of the cluster, except for the UV range. The predicted magnitudes of these proto-GCs are mag AB ∼28-30 between 0.7 and 8 µm and for redshifts z ∼ 4 − 10, which is detectable with the JWST. The peculiar observational features of cool SMSs imply that they might in principle be detected in color-color diagrams that probe the spectral energy distribution below and above the Balmer break. Conclusions.Our results show that SMSs should be detectable in proto-GCs if they are luminous and relatively cool. They may be found through deep imaging with the JWST.

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Section: Comparison With Other Resultssupporting

confidence: 54%

Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift

Martins

Haemmerlé

Charbonnel

2019

A&A

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“…Upcoming next generation telescopes e.g. James Webb Space Telescope (JWST), Euclid and WFIRST will be able to detect SMSs at 𝑧 ∼ 6 − 20 (Surace et al 2018(Surace et al , 2019Woods et al 2020;Martins et al 2020). The number of SMSs per unit redshift per unit solid angle, which are expected to be detected at a redshift 𝑧, is given by:…”

Section: Introductionmentioning

confidence: 99%

“…At present the 𝑛 SMS is very poorly constrained. SMSs could be observed both to be cool and red or hot and blue (Surace et al 2018(Surace et al , 2019. Whether an observed SMS will be red or blue depends on how quickly and persistently the SMS is growing, whether it is rapidly accreting gas from an atomic-cooling halo or growing from runaway collisions in a stellar cluster.…”

Section: Introductionmentioning

confidence: 99%

Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions

Das,

Schleicher,

Leigh

et al. 2020

Preprint

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More than two hundred supermassive black holes (SMBHs) of masses 10 9 M have been discovered at 𝑧 6. One promising pathway for the formation of SMBHs is through the collapse of supermassive stars (SMSs) with masses ∼ 10 3−5 M into seed black holes which could grow upto few times 10 9 M SMBHs observed at 𝑧 ∼ 7. In this paper, we explore how SMSs with masses ∼ 10 3−5 M could be formed via gas accretion and runaway stellar collisions in high-redshift, metal-poor nuclear star clusters (NSCs). We explore physically motivated accretion scenarios, e.g. Bondi-Hoyle-Lyttleton accretion and Eddington accretion, as well as simplified scenarios such as constant accretions. While gas is present, the accretion timescale remains considerably shorter than the timescale for collisions with the most massive object (MMO). However, overall the timescale for collisions between any two stars in the cluster can become comparable or shorter than the accretion timescale, hence collisions still play a crucial role in determining the final mass of the SMSs. We find that the problem is highly sensitive to the initial conditions and our assumed recipe for the accretion, due to the highly chaotic nature of the problem. The key variables that determine the mass growth mechanism are the mass of the MMO and the gas reservoir that is available for the accretion. Depending on different conditions, massive objects of masses ∼ 10 3−5 M can form for all three accretion scenarios considered in this work.

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“…The exception would be the rare case of a supermassive (𝑀 ∼ 10 5 𝑀 ) Population III star (Haemmerlé et al 2018). These gargantuan stars, considered already in the 1960s as direct sources of the, by then, newly discovered quasi-stellar objects (although argued as dynamically unstable by e.g., Chandrasekhar 1964) now also offer a venue of direct detection of Pop III stars, their supernovae or their resulting direct collapse black holes with only mild magnifications or even without the help of gravitational lensing (Surace et al 2018(Surace et al , 2019Whalen et al 2020).…”

Section: Introductionmentioning

confidence: 99%

Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid

Vikaeus,

Zackrisson,

Schaerer

et al. 2021

Preprint

Self Cite

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Dark matter halos that reach the HI-cooling mass without prior star formation or external metal pollution represent potential sites for the formation of small Population III galaxies at high redshifts. Such objects are expected to attain total stellar masses of at most 10 6 solar masses and will therefore typically be extremely faint. Gravitational lensing may in rare cases boost their fluxes to detectable levels, but to find even a small number of such objects requires very large sky areas to be surveyed. Because of this, a small, wide-field telescope can in principle offer better detection prospects than a large telescope with a smaller field of view. Here, we derive the Pop III galaxy properties -in terms of comoving number density, stellar initial mass function and total stellar mass -required to allow gravitational lensing to lift such objects at redshift 𝑧 = 5 − 16 above the detection thresholds of blind surveys carried out with the James Webb space telescope (JWST), the Roman space telescope (RST) or Euclid. We find that the prospects for photometric detections of Pop III galaxies are promising, and that they are better for RST than for JWST and Euclid. However, the Pop III galaxies favoured by current simulations have number densities too low to allow spectroscopic detections based on the strength of the HeII1640 emission line in any of the considered surveys unless very high star formation efficiencies (𝜖 0.1) are envoked.

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On the detection of supermassive primordial stars – II. Blue supergiants

Cited by 27 publications

References 91 publications

Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift

Spectral properties and detectability of supermassive stars in protoglobular clusters at high redshift

Formation of supermassive black hole seeds in nuclear star clusters via gas accretion and runaway collisions

Conditions for detecting lensed Population III galaxies in blind surveys with the James Webb Space Telescope, the Roman Space Telescope and Euclid

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