Skip to Main Content

PhD Proposal: Adam Harvey

Friday, May 25, 2018
10:00 AM - 12:00 PM
Physics : 401
ADVISOR: Dr. Markos Georganopoulos

TITLE: Measuring the Total Light in the Universe and Understanding Blazar Emission

ABSTRACT:We propose here two projects; one regarding the total light in the Universe and its cosmological implications; the other regarding the emission of high-energy radiation from blazars.

As to the first project, stars emit light in the optical-ultraviolet (optical-UV), and they heat dust which then radiates in the infrared (IR). This forms an isotropic, diffuse background radiation. This background radiation is called the extragalactic background light (EBL), and its spectrum and cosmological evolution are dependent on the cosmological evolution of star formation (and thus structure formation, in turn). Gamma-ray photons can pair-produce with photons in the EBL. Information about the intrinsic spectrum of gamma-ray emitting sources (blazars, introduced below) can be used to infer the optical depth due to this pair-production process, and thus the EBL. We here attempt to constrain the EBL using, for the first time, a model-independent realization of this method.

Our second project regards the high-energy, gamma-ray (∼GeV) emission observed from blazars. A blazar is an active galactic nucleus (AGN) which hosts a jet of relativistic particles which is oriented close to our line-of-sight (LOS). By being oriented close to our LOS, blazars show observable amounts of gamma-ray emission due to relativistic beaming. The location in the blazar at which this gamma-ray emission occurs is an open question; knowledge of the emission location would help us understand the formation and collimation of blazar jets. We have derived a parameter composed solely of observable quantities which can help constrain both the emission location and emission mechanism of gamma-rays in blazars. We present here our preliminary work on evaluating this parameter for three different samples of blazars.