21cm Cosmology: The End of the Beginning
1 LeConte Hall
Aaron Parsons (UCB)
Since it was first proposed nearly two decades ago, measuring 21cm emission from neutral hydrogen in our early universe has tantalized us as a powerful probe of both cosmology and astrophysics. While the science case for 21cm cosmology, particularly during the Epoch of Reionization, is well established, the technical path toward measuring this signal has been more problematic. PAPER has recently distanced itself from its competitors, applying major technical breakthroughs to set the first physically meaningful upper limits on 21cm emission during reionization, and improving those limits a year later to show the presence of significant early heating. Even as PAPER's final season is under analysis, we are re-tooling our array to become HERA. New, 14-m dishes are replacing PAPER's smaller elements, giving HERA the sensitivity to drive beyond the detection phase of 21cm cosmology, into the exciting era of data-driven modeling. The results will revolutionize our understanding of galaxy and star formation and even improve upon CMB cosmology.