3:30–5:00 pm ERC 161
Title: Progress towards measuring the optical depth to reionization with hydrogen 21 cm fluctuations
Abstract: The optical depth to reionization (“tau”) parameterizes the most important event in the universe after recombination but is the least constrained of the standard six parameters of Lambda-CDM cosmology. Uncertainty in this parameter limits the ability of CMB measurements to constrain the sum of the neutrino masses, among other extensions to LCDM. While errors on tau are expected to improve from future CMB measurements alone, it would be extremely valuable to have an independent measurement. Many groups have been pursuing detection of the hydrogen 21 cm hyperfine structure line at high redshift as a tracer of the state of the intergalactic medium during the “epoch of reionization”, the formation period of the first stars, galaxies, and black holes. Apart from the intrinsic interest of studying this epoch, 21 cm measurements, particularly the power spectrum, hold the promise of significantly reducing the error on the cosmic “nuisance parameter” tau, since this epoch contributes the bulk of the column density to tau. I will discuss the theoretical motivation for measuring tau with 21 cm power spectra and work we have done in characterizing the model dependence of the inference. I will review the general state of attempts to measure the 21 cm power spectrum, with a focus on the Hydrogen Epoch of Reionization Array (HERA). I will discuss upcoming results from HERA and challenges remaining on the instrument side. I conclude with prospects for substantially improving tau errors in the next several years.
Zoom: https://uchicago.zoom.us/j/93092711418?pwd=ax8GAGcDkGPBQj9fe0P8I7TS1shSIl.1
