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

Fabio Pacucci*, Pratika Dayal, Yuichi Harikane, Akio K. Inoue, Abraham Loeb

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

9 Citations (Scopus)


The detection of two z ∼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 × 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 ∼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 $\sim 10^8 \, \rm M_\odot$ accreting at or slightly above the Eddington rate (fEdd ∼1.0). This black hole mass at z ∼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.

Original languageEnglish
Pages (from-to)L6-L10
JournalMonthly Notices of the Royal Astronomical Society: Letters
Issue number1
Publication statusPublished - 2022 Jul 1


  • galaxies: high-redshift
  • galaxies: luminosity function
  • galaxies: starbursts
  • quasars: supermassive black holes

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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