Are the newly-discovered z ∼ 13 drop-out sources starburst galaxies or quasars

The detection of two z similar to 13 galaxy candidates 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 5-24 xhigher 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 similar to 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 similar to 10(8) M similar to accreting at or slightly above the Eddington rate (f Edd similar to 1.0). This black hole mass at z similar to 13 would require very challenging, but not implausible, growth parameters. If spectroscopically confirmed, these two sources will represent a remarkable laboratory to study the Universe at previously inaccessible redshifts.

Automated summary

The detection of two z similar to 13 galaxy candidates has provided new insights into the formation of galaxies in the early universe. The study explores the possibility of these sources being star forming galaxies or quasars. The results suggest that the observed sources could be extreme star-formers with significantly higher star formation rates than expected, or they could be powered by black holes accreting at high rates. These findings, if spectroscopically confirmed, will offer a unique opportunity to study the Universe at previously inaccessible redshifts.