Asmus, D., Greenwell, C.L., Gandhi, P., Boorman, P.G., Aird, J., Alexander, D.M., Assef, R.J., Baldi, R.D., Davies, R.I., Hönig, S.F., Ricci, C., Rosario, D.J., Salvato, M., Shankar, F. and Stern, D. (2020) Local AGN Survey (LASr): I. Galaxy sample, infrared colour selection and predictions for AGN within 100 Mpc. Monthly Notices of the Royal Astronomical Society, 494 (2), 1784–1816. (doi:10.1093/mnras/staa766).
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 per cent 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 per cent of known luminous AGN. These 49k galaxies serve as parent sample for LASr, called LASr-GPS. It contains 4.3k already known AGN, ≥82 per cent 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 per cent reliability. This includes 61 new AGN candidates and implies an optical type 2 fraction of 50–71 per cent. We quantify the efficiency of this technique and estimate the total number of AGN with Lint(2−10keV)≥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 per cent 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.
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