The predicted properties of helium-enriched globular cluster progenitors at high redshift

• Published in: Monthly notices of the Royal Astronomical Society 2020-08, Vol.496 (3), p.3222-3234
• Main Authors: Nataf, David M, Horiuchi, Shunsaku, Costa, Guglielmo, Wyse, Rosemary F G, Ting, Yuan-Sen, Crocker, Roland, Federrath, Christoph, Chen, Yang
• Format: Article
• Language: English
• Subjects: Astronomy & Astrophysics; ASTRONOMY AND ASTROPHYSICS; globular clusters: general
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/staa1351

ABSTRACT Globular cluster progenitors may have been detected by Hubble Space Telescope, and are predicted to be observable with James Webb Space Telescope (JWST) and ground-based extremely large telescopes with adaptive optics. This has the potential to elucidate the issue of globular cluster formation and the origins of significantly helium-enriched subpopulations, a problem in Galactic astronomy with no satisfactory theoretical solution. Given this context, we use model stellar tracks and isochrones to investigate the predicted observational properties of helium-enriched stellar populations in globular cluster progenitors. We find that, relative to helium-normal populations, helium-enriched (ΔY = +0.12) stellar populations similar to those inferred in the most massive globular clusters, are expected, modulo some rapid fluctuations in the first ∼30 Myr, to be brighter and redder in the rest frame. At fixed age, stellar mass, and metallicity, a helium-enriched population is predicted to converge to being ∼0.40 mag brighter at $\lambda \approx 2.0\, {\mu \rm m}$, and to be 0.30-mag redder in the JWST–NIRCam colour (F070W − F200W), and to actually be fainter for $\lambda \lesssim 0.50 \, {\mu \rm m}$. Separately, we find that the time-integrated shift in ionizing radiation is a negligible $\sim \!5{{\ \rm per\ cent}}$, though we show that the Lyman-α escape fraction could end up higher for helium-enriched stars.