Constraining Very High Mass Population III Stars through He II Emission in Galaxy BDF-521 at z = 7.01

Abstract

Numerous theoretical models have long proposed that a strong He II 1640 emission line is the most prominent and unique feature of massive Population III (Pop III) stars in high redshift galaxies. The He II 1640 line strength can constrain the mass and IMF of Pop III stars. We use F132N narrowband filter on the Hubble Space Telescope's (HST) Wide Field Camera 3 (WFC3) to look for strong He II lambda 1640 emission in the galaxy BDF-521 at z=7.01, one of the most distant spectroscopically-confirmed galaxies to date. Using deep F132N narrowband imaging, together with our broadband imaging with F125W and F160W filters, we do not detect He II emission from this galaxy, but place a 2-sigma upper limit on the flux of 5.3x10^-19 ergs s^-1 cm^-2. This measurement corresponds to a 2-sigma upper limit on the Pop III star formation rate (SFR_PopIII) of ~ 0.2 M_solar yr^-1, assuming a Salpeter IMF with 50< M/M_solar < 1000. From the high signal-to-noise broadband measurements in F125W and F160W, we fit the UV continuum for BDF-521. The spectral flux density is ~ 3.6x 10^-11 lambda^-2.32 ergs s^-1 cm^-2 A^-1, which corresponds to an overall unobscured SFR of ~ 5 M_solar yr^-1. Our upper limit on SFR_PopIII suggests that massive Pop III stars represent < 4% of the total star formation. Further, the HST high resolution imaging suggests that BDF-521 is an extremely compact galaxy, with a half-light radius of 0.6 kpc.

14 pages, 2 figures, Accepted for Publication in ApJL

References in corpus (4)

• The Formation of Population III Binaries from Cosmological Initial Conditions
• A galaxy at a redshift z = 6.96
• Searching for the reionization sources
• A photometric survey for Lyalpha-HeII dual emitters: Searching for Population III stars in high-redshift galaxies

Cited by in corpus (5)

• Spectroscopic properties of luminous Lyman-α emitters at $z\approx 6-7$ and comparison to the Lyman-break population
• A strong He II $\lambda$1640 emitter with extremely blue UV spectral slope at $z=8.16$: presence of Pop III stars?
• A Metal-Free Galaxy at $z=3.19$? Evidence of Late Population III Star Formation at Cosmic Noon
• Deciphering stellar metallicities in the early Universe: Case study of a young galaxy at z = 4.77 in the MUSE eXtremely Deep Field
• Deep Hubble Space Telescope Imaging on the Extended Ly$\alpha$ Emission of a QSO at $z=2.19$ with Damped Lyman Alpha System as a Natural Coronagraph