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arXiv · 2201.00823

Are the Newly-Discovered $z \sim 13$ Drop-out Sources Starburst Galaxies or Quasars?

Fabio Pacucci·Pratika Dayal·Yuichi Harikane·Akio K. Inoue·Abraham Loeb
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Abstract

The detection of two $z\sim 13$ 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 $5-24\times$ 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 $z\sim13$ 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.

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Fabio Pacucci, Pratika Dayal, Yuichi Harikane, Akio K. Inoue, Abraham Loeb. 2022-01-03. Are the Newly-Discovered $z \sim 13$ Drop-out Sources Starburst Galaxies or Quasars?. https://doi.org/10.1093/mnrasl%2Fslac035

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