http://arxiv.org/abs/2201.00823
The detection of two $z \sim 13$ galaxy candidates (Harikane et al. 2021b) has opened a new window on galaxy formation at an era only $330$ Myr after the Big Bang. Here, we investigate the physical nature of these sources: are we witnessing star forming galaxies or quasars at such early epochs? If powered by star formation, the observed ultraviolet (UV) luminosities and number densities can be jointly explained if: (i) these galaxies are extreme star-formers with star formation rates $5-25\times$ higher than those expected from extrapolations of average lower-redshift relations; (ii) the star formation efficiency increases with halo mass and is countered by increasing dust attenuation from $z \sim 10-5$; (iii) they form stars with an extremely top-heavy initial mass function. The quasar hypothesis is also plausible, with the UV luminosity produced by black holes of $\sim 10^8 \, \mathrm{M_{\odot}}$ accreting at or slightly above the Eddington rate ($f_{\rm Edd}\sim 1.0$). This black hole mass at $z \sim 13$ would require challenging, but not implausible, growth parameters, in line with what required for $z\sim 7.5$ quasars detected thus far. If spectroscopically confirmed, these two sources will represent a remarkable laboratory to study the Universe at previously inaccessible redshifts.
F. Pacucci, P. Dayal, Y. Harikane, et. al.
Wed, 5 Jan 22
30/54
Comments: 5 pages, 3 figures, submitted to MNRAS Letters
You must be logged in to post a comment.