Two speakers: Mackenzie Jones (Dartmouth) and Lena Murchikova (CalTech)

Monday, September 25, 12:05pm
Marlar Lounge 37-252

Is black hole growth a universal process? Exploring selection effects in measurements of supermassive black hole accretion rates and host galaxies.
Speaker: Mackenzie Jones, Dartmouth

At the center of essentially every massive galaxy is a monstrous black hole producing luminous radiation driven by the accretion of gas. These active galactic nuclei (AGN) can influence the evolution of their host galaxies, and by observing them we may trace the growth of black holes across cosmic time. However, our knowledge of the full underlying AGN population is hindered by complex observational biases that are difficult to untangle using conventional methods and theoretical models. My research attempts to untangle these biases by using a novel approach to simulate the impact of selection effects on multi-wavelength observations.

The most statistically powerful studies of AGN to date come from optical spectroscopic surveys, with some reporting a complex relationship between AGN accretion rates and host galaxy characteristics. However, the optical waveband can be strongly influenced by selection effects and dilution from host galaxy star formation. I have shown that when selection effects are accounted for in an optically selected AGN population, the Eddington ratio distribution is consistent with a broad power-law, as seen in the X-rays (Jones et al. 2016). This suggests that a simplistic mode of AGN accretion based on a universal Eddington ratio distribution may be enough to describe the full multi-wavelength AGN population.

Probing the Black Hole in the Center of Our Galaxy with Hydrogen Recombination Lines
Speaker: Lena Murchikova, CalTech

To more completely explore the impact of selection effects, I have expanded a semi-numerical galaxy formation simulation to include this straightforward prescription for AGN accretion and explicitly model selection effects. I have found that a simple model for AGN accretion can broadly reproduce the host galaxies and halos of the X-ray AGN population, and that different AGN selection techniques yield samples with very different host galaxy properties (Jones et al. 2017). Finally, I will discuss the capabilities of this simulation to build synthetic X-ray and multi wavelength SEDs in order to explore the synthesis of the X-ray background and the AGN populations that would be detected with the next generation of observatories.