Local AGN Survey (LASr) : I. Galaxy sample, infrared colour selection and predictions for AGN within 100 Mpc.

Abstract

To answer major questions on supermassive black hole (SMBH) and galaxy evolution, a complete census of SMBH growth, i.e., active galactic nuclei (AGN), is required. Thanks to all-sky surveys by the Wide-field Infrared Survey Explorer (WISE) and the Spectrum-Roentgen-Gamma (SRG) missions, this task is now feasible in the nearby Universe. We present a new survey, the Local AGN Survey (LASr), with the goal of identifying AGN unbiased against obscuration and determining the intrinsic Compton-thick (CT) fraction. We construct the most complete all-sky galaxy sample within 100 Mpc (90% completeness for log (M*/M⊙) ∼ 9.4), four times deeper than the current reference, the Two Micron All-Sky Survey Redshift Survey (2MRS), which misses ∼20% of known luminous AGN. These 49k galaxies serve as parent sample for LASr, called LASr-GPS. It contains 4.3k already known AGN, ≥82% of these are estimated to have Lnuc(12μm) < 1042.3 erg s−1, i.e., are low-luminosity AGN. As a first method for identifying Seyfert-like AGN, we use WISE-based infrared colours, finding 221 galaxies at Lnuc(12μm) ≥ 1042.3 erg s−1 to host an AGN at 90% reliability. This includes 61 new AGN candidates and implies and optical type 2 fraction of 50–71%. We quantify the efficiency of this technique and estimate the total number of AGN with Lint(2-10  keV) ≥ 1042 erg s−1 in the volume to be 362+145−116 (⁠8.6+3.5−2.8× 10−5 Mpc−3). X-ray brightness estimates indicate the CT fraction to be 40–55% to explain the Swift non-detections of the infrared selected objects. One third of the AGN within 100 Mpc remain to be identified, and we discuss the prospects for the eROSITA all-sky survey to detect them.