Peiyuan Mao

Peiyuan Mao's picture
Graduate Student Year 6 (Urry)
EVN 304
Ph.D. 2017, Yale University
Field of Study: 
Thesis Advisor: 
Meg Urry
Dissertation Title: 
Blazar Demographics: Intrinsic Properties of Jet-Dominated Active Galactic Nuclei
Dissertation Abstract: 

Blazars with their Doppler-boosted relativistic jets are perfect laboratories to study jet physics and provide crucial insights into jet mechanism, black hole spin, and growth history of the host galaxy. However, the blazar samples we observe are highly biased subsets of the true population because of the complicated shape of their spectral energy distributions. Thus to infer the intrinsic properties of blazars we have to extrapolate from the biased samples — and there are two opposing theories about the correct way to do this extrapolation: one in which the synchrotron-radiating electron energies are linked to the total jet power, the other in which they are independent. My dissertation is a thorough investigation of the intrinsic properties of blazars, from their spectral energy distributions to their luminosity functions to their cosmic evolution.

In particular, I collected data for the largest collection of blazars to date, i.e., every single BL Lac object and flat-spectrum radio quasar in the literature; reduced new X-ray data for the majority; and developed a statistical description of blazar SEDs. Using the deepest and most complete radio-selected sample of flat-spectrum radio quasars, I constructed a new luminosity function of this population, based on a sample more than twice as large as previous work, using a maximum likelihood estimation method rather than fitting to binned data.
Combining the SED information with the luminosity function, I carried out Monte Carlo simulations populating the universe with blazars and sampling them at different wavelengths and flux limits (corresponding to real surveys). Our analysis conclusively ruled out any model that assumes an independence between blazar SED and luminosity, and showed that SEDs and radio luminosities must be related in order to obtain the observed blazar distribution. We also explain the observed difference in the cosmic evolution of some BL Lac objects from other blazars as a simple selection effect that follows naturally from the SED shape.

The most important implication of this work concerns the true demographics of the blazar population, namely, that low-power jets are far more common than high-power jets. This is a critical constraint on models for jet production and propagation.

Degree Date: 
May, 2017