X-ray surveys: Soft to Hard - probing obscured black hole growth over cosmic time
Abstract
I will review recent results from large X-ray surveys that probe the evolution of Active Galactic Nuclei (AGNs) at both soft and hard X-ray energies and provide crucial insights into obscured black hole growth over cosmic time. Chandra and XMM-Newton have provided the most sensitive X-ray surveys to date, probing from 0.5-8 keV in energy. However, these surveys still suffer complex selection effects against obscured AGNs. A number of recent studies have developed new techniques, exploiting the soft-to-hard energy coverage of Chandra and XMM-Newton, to address these selection biases and provide accurate measurements of the evolution of the AGN luminosity function and the distribution of obscuring column densities (the "NH function"). These studies show that the bulk of black hole growth took place at high redshifts (z>1) and is obscured, although the fraction of the most heavily obscured, Compton-thick AGNs and its evolution remains somewhat uncertain. Moving to harder energies, the NuSTAR observatory is providing the first high-sensitivity X-ray surveys at >8keV, enabling new studies of the evolution of obscured AGN to high redshifts. I will give an overview of the results from the NuSTAR survey program, including the first measurements of the evolution of the AGN luminosity function at >8keV, constraints on the fraction of obscured and Compton-thick AGNs, and studies of the spectral properties of AGNs at these hard energies. Finally, I will briefly discuss future missions, in particular the Athena X-ray observatory that will probe obscured black hole growth out to very high redshifts.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E..46A