LUNAR webinar, 9th Nov. 2012

Jordan Mirocha (CU Boulder)

Constraining the First Stars and Super-Massive Black Holes with the Global 21-cm Spectrum from High Redshift



Nearly all of our knowledge about the early universe comes from the observable signatures of two phase transitions: recombination at z∼1100 and the late stages of cosmic reionization at z∼6. The 21-cm spin-flip transition of neutral hydrogen is a potentially powerful probe of the intervening billion years, in which the first stars, black holes, and galaxies form. Simple models for the sky-averaged 21-cm spectrum predict a signal with three inflection points driven by astrophysical processes, which occur prior to the completion of reionization. However, interpreting these features will be challenging due to degeneracies among model parameters. In this talk, I will discuss the possibility of disentangling star formation and black hole growth histories using the 21-cm background in conjunction with constraints from the cosmic X-ray background and observations of high redshift quasars. Future missions like the Dark Ages Radio Explorer, uniquely situated above the radio-quiet lunar farside, have the best chance of constraining cosmic evolution at z>10, which I will highlight as the most straightforward part of the 21-cm signal to decipher.