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Resolving Discrepancies in Black Hole Spin Measurements and Black Holes in the Pre-Reionization Era: Signatures in the Sky-Averaged 21-cm Signal

Event Details

Event Dates: 

Friday, December 12, 2014 - 12:00pm

Seminar Location: 

  • CASA Conference Room C324

Speaker Name(s): 

Greg Salvesen
Jordan Mirocha

Speaker Affiliation(s): 

Seminar Type/Subject

Scientific Seminar Type: 

  • Astrophysics Lunch Seminar

Event Details & Abstract: 

---- Talk by Greg Salvesen

Title: Resolving Discrepancies in Black Hole Spin Measurements

Abstract: There are two well-established and independent techniques used to measure the angular momentum, or spin, of a black hole. One relies on fitting the relativistically broadened iron emission line and the other requires fitting the accretion disk continuum and independently measuring the black hole mass, distance, and inner disk inclination. When each technique is applied to the same black hole, the measured spins are often discrepant. This issue must be alleviated before either black hole spin measurement method may be deemed robust. I am wrapping up a project demonstrating that these black hole spin measurement discrepancies can be resolved by relaxing certain assumptions from the disk continuum method.

---- Talk by Jordan Mirocha

Title: Black Holes in the Pre-Reionization Era: Signatures in the Sky-Averaged 21-cm Signal

Abstract: Within the first ~billion years after the Big Bang, the intergalactic medium (IGM) underwent a remarkable transformation, from a uniform sea of cold neutral hydrogen gas to a fully ionized, metal-enriched plasma. Three milestones during this epoch of reionization -- the emergence of the first stars, black holes (BHs), and full-fledged galaxies -- are expected to manifest themselves as extrema in sky-averaged measurements of the redshifted 21-cm background. I will focus on one of these milestones -- the emergence of the universe's first black holes -- and show that reasonable changes in the characteristic mass of accreting black holes affects the sky-averaged 21-cm signal at a level accessible to first-generation experiments. Unfortunately, poorly constrained processes such as Comptonization in accretion disk atmospheres and neutral absorption in the interstellar medium of high redshift galaxies may have an equally important impact on the 21-cm signal. I will present preliminary results of a parameter study aimed at quantifying such degeneracies, and assess their impact on the interpretation of near-future datasets.