Extragalactic Archeology: Linking Active Galactic Nuclei to Dark Matter Halos over Cosmic Time

• Applicant: Dr. Mirko Krumpe
• Subject Area: Astrophysics and Astronomy
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 265092751

I propose to measure, for the first time, how galaxies with growing supermassive black holes populate dark matter halos as a function of cosmic time. I will derive, in three independent redshift ranges (median redshifts: ~0.03, ~0.3, and ~2.3), the minimum dark matter halo mass required to host an active galactic nucleus (AGN) and the number of AGN as a function of halo mass. Both parameters encode information on the physical mechanism that turns a normal galaxy into an AGN. The repeating AGN phase is thought to play a fundamental role in the evolution of galaxies.I will measure the quantities with high precision using cross-correlation functions between AGN samples and large sets of galaxies in the same volume, and subsequently perform AGN halo occupation distribution modeling. My team pioneered this method and demonstrated its success at intermediate redshifts (~0.3) using the Sloan Digital Sky Survey. Newly published AGN data from the Swift satellite mission are publicly accessible to perform this measurement with Two Micron All Sky Survey galaxies at low redshifts (~0.03). For high redshifts, no large galaxy samples have been available so far. Forthcoming data from the Hobby-Eberly Telescope Dark Energy Experiment will enable me, for the first time, to carry out such a measurement also at high redshifts (~2.3). By combining the results at the three different redshifts, I will be able to map the evolution of the minimum halo mass needed to host an AGN and the number of AGN with halo mass over the last ~11 Gyr, i.e., 80% of the universe's lifetime. In addition, I will predict both parameters as a function of cosmic time based on different physicalAGN triggering mechanisms using cosmological simulations. Besides the commonly considered mechanisms to ignite an AGN at the center of a normal galaxy, e.g., galaxy mergers, accretion of hot diffuse gas, and secular instabilities, the project will also allow me to explore alternative scenarios. The comparison of the simulated results with the observed findings at the three redshifts will enable me to discriminate between currently favored AGN triggering scenarios and to identify the underlying physical mechanism that best represents the observations. Exploring the evolution of the minimum halo mass and the number of AGN with halo mass over cosmic time provides a novel, previously unexplored approach to studying the physics involved in AGN triggering. This project will deliver urgently needed additional constraints at various redshifts to distinguish several recently developed theoretical models that try to explain the observed AGN distribution in the universe and in dark matter halos. The results of this project will have profound consequences, not only for our understanding of the AGN triggering mechanisms, but also for how supermassive black holes grow at high redshifts, and which physics can affect a galaxy over 80% of the universe's lifetime.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Lutz Wisotzki