Contribution to the 2022 Cosmology session of the 56th Rencontres de
  Moriond: Reionization constraints from HERA 21cm power spectrum limits
  I present our analysis of the 21cm power spectrum upper limits from the HERA
radio interferometer, published in HERA Collaboration et al. 2022. We use the
recent limits to constrain reionization and the properties of the IGM and
galaxies in the early universe. I focus in particular on the possibility of a
radio background in addition to the CMB (e.g. produced by early galaxies) which
can lead to a stronger 21cm signal and is thus easier to constrain. I show what
limits the HERA observations can put on these models and the IGM, and how this
compares to existing constraints on the radio and X-ray background.
