Catalog of very-high-energy emitting active galactic nuclei at high Galactic latitudes

TL;DR

This paper presents a comprehensive catalog of 175 high-confidence VHE gamma-ray emitting AGN at high Galactic latitudes, including many new detections, and analyzes their luminosity function and spatial density.

Contribution

It provides the first unbiased survey of VHE AGN using Fermi LAT data, expanding the known population and characterizing their properties and distribution.

Findings

90% of VHE AGN are BL Lac objects

175 sources detected, including 71 previously known

The luminosity function indicates a spatial density of (6.5±0.5)e-7 Mpc^-3

Abstract

Large number of Active Galactic Nuclei (AGN) producing Very-High-Energy (VHE) gamma-rays (energies above 100~GeV) has been revealed using observations with Imaging Atmospheric Cherenkov Telescopes (IACTs). However, our knowledge of the VHE emitting AGN population is limited in the absence of an unbiased sky survey. We use long exposure of Fermi Large Area Telescope (LAT) to perform a survey of VHE emitting AGN at Galactic latitudes |b|>10 degrees. We consider clustering of gamma-ray events with energies E>100 GeV around positions of AGN from the 4-th LAT source catalog to select sources detected in the VHE range. The VHE AGN catalog produced in this way contains overall 175 sources detected with high confidence and additional 100 sources detected at more than 3-sigma level. It is 90% complete at the flux limit 1.3e-12 erg/cm2s. Less than half of the source sample (71) are previously reported VHE emitters, other sources are new detections in the VHE band. The majority of VHE AGN detectable at the survey flux limit are BL Lac type objects. We find their luminosity function to derive their spatial density (6.5+/-0.5)e-7/ Mpc3 and the characteristic luminosity scale ~1e44 erg/s. Ten sources in the VHE AGN catalog are nearby radio galaxies and seven are flat spectrum radio quasars, while 20 sources are unclassified AGN. We also include in our catalog four unidentified sources that may or may not be VHE AGN. 63 source in the catalog are "extreme" blazars, with 41 of them being new VHE band detections. In spite of the fact that the VHE flux is heavily attenuated by the pair production in interactions with Extragalactic Background Light (EBL), the catalog includes 7 sources at redshift larger than 1. Some of these sources show peculiar hardening of the VHE band spectra that point either to errors in redshift determination, or to limitations of modeling of cosmological evolution of EBL.