Black Holes of the First Stars

Abstract: In this report, we constrain properties of foreground objects in the Milky Way that have the potential of being confused with accretion disks of Population III stellar- mass black holes at high redshift. Following Windhorst et al. (2018), a model for multicolour accretion disks of Population III stellar-mass black holes is presented. The resulting spectra are used to derive observable magnitudes with the James Webb Space Telescope (JWST). Magnification of a factor 103 to 106, depending on the black hole mass, through gravitational lensing is necessary to surpass the JWST detection limit. Spectra of faint Milky Way objects of low-mass main sequence or pre-main sequence stars (Baraffe et al. 2015) and cool brown dwarfs and giant exoplanets (Phillips et al. 2020) were fitted to a distance such that their observable JWST magnitudes are similar to those of the accretion disk. We find that the spectral energy distributions that have the highest chances of being confused with high redshift Population III black hole accretion disks belong to pre-main sequence and low-mass main sequence stars of temperature 1500 K to 4200 K. At redshift