The High Energy X-ray Probe (HEX-P): Resolving the X-ray background at its peak

HEX-P is a probe-class mission concept that will combine high spatial resolution X-ray imaging (<10 arcsec FWHM) and broad spectral coverage (0.1-150 keV) with an effective area far superior to current facilities (including XMM-Newton and NuSTAR), to enable revolutionary new insights into a variety of important astrophysical problems.

A key science goal for HEX-P is to understand the growth of supermassive black holes (SMBHs) across cosmic time and its connection with galaxy evolution. HEX-P will devote a significant portion of time to extragalactic surveys in a typical wedding cake style to detect for the first time the Seyfert-luminosity AGN population in hard X-rays at cosmic noon (luminosities ~10⁴³ erg/s in the 10-40 keV band) that we have been missing so far.

We will present the properties of deep and wide HEX-P extragalactic surveys, which we simulated with the SIXTE software package and the most recent set of calibration files available for HEX-P. The simulated fields are seeded with both AGN mock catalogs based on derived from population synthesis models, and with as well as real data from previous surveys with Chandra, NuSTAR and XMM-Newton. By using the established source detection techniques applied in previous NuSTAR surveys (e.g., COSMOS, ECDFS, UDS, JWST-NEP), we will showcase HEX-P’s ability to resolve >60% of the AGN population contributing to the peak of the Cosmic X-ray Background. Such studies are crucial to obtain the measurement of the total accretion power in the Universe as well as to construct more sensitive population synthesis models of SMBH growth in the context of the evolution of their host galaxies as probed by a range of multi-wavelength observations. Future cosmological surveys with HEX-P are hence extremely complementary with the plethora of surveys planned with next-generation instruments such as the 4-meter Multi-Object Spectroscopic Telescope, the James Webb Space Telescope and the Nancy Grace Roman Space Telescope.

More information on HEX-P, including the full team list, is available at https://hexp.org.