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Local AGN Survey (Lasr): I. Galaxy Sample, Infrared Colour Selection and Predictions for AGN Within 100 Mpc

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Local AGN Survey (Lasr): I. Galaxy Sample, Infrared Colour Selection and Predictions for AGN Within 100 Mpc MNRAS 000,1–30 (2020) Preprint 16 March 2020 Compiled using MNRAS LATEX style file v3.0 Local AGN Survey (LASr): I. Galaxy sample, infrared colour selection and predictions for AGN within 100 Mpc D. Asmus,1;2? C. L. Greenwell,1 P. Gandhi,1 P. G. Boorman,1;3 J. Aird,4 D. M. Alexander,5 R. J. Assef,6 R. D. Baldi,1;7;8 R. I. Davies,9 S. F. Hönig,1 C. Ricci,4 D. J. Rosario,4 M. Salvato,8 F. Shankar,1 and D. Stern10 1Department of Physics & Astronomy, University of Southampton, Hampshire SO17 1BJ, Southampton, United Kingdom 2European Southern Observatory, Casilla 19001, Santiago 19, Chile 3Czech Academy of Sciences, Národní 3, 117 20 Staré Mesto, Czechia 4Department of Physics & Astronomy, University of Leicester, University Road, Leicester LE1 7RJ, UK 5Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham, DH1 3LE, UK 6Núcleo de Astronomía de la Facultad de IngenierÃŋa y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago 7Dipartimento di Fisica, Universitá degli Studi di Torino, via Pietro Giuria 1, 10125 Torino, Italy 8INAF - Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, I-00133 Roma, Italy 9Max Planck Institute for Extraterrestrial Physics(MPE), Giessenbachstr. 1, 85748 Garching, Germany 10Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA Accepted 2020 Mar 12. Received 2019 Dec 19 ABSTRACT In order to answer some of the major open questions in the fields of supermassive black hole (SMBH) and galaxy evolution, a complete census of SMBH growth, i.e., active galactic nuclei (AGN), is required. Thanks to deep all-sky surveys, such as those by the Wide-field Infrared Survey Explorer (WISE) and the Spectrum-Roentgen-Gamma (SRG) missions, this task is now becoming feasible in the nearby Universe. Here, 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. First, we construct the most complete all-sky sample of galaxies within 100 Mpc from astronomical databases (90% completeness for log¹M∗/M º ∼ 9:4), four times deeper than the current local galaxy reference, the Two Micron All-Sky Survey Redshift Survey (2MRS), which turns out to miss ∼ 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 Lnuc¹12 µmº < 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 Lnuc¹12 µmº ≥ 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 to 71%. We quantify the efficiency of this technique and estimate the total number of Lint¹ º ≥ 42 −1 +145 : +3:5 × −5 −3 AGN with 2-10 keV 10 erg s in the volume to be 362−116 (8 6−2:8 10 Mpc ). 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. Key words: galaxies: active – galaxies: Seyfert – infrared: galaxies – X-rays: galaxies arXiv:2003.05959v1 [astro-ph.GA] 12 Mar 2020 1 INTRODUCTION as the stellar velocity dispersion or stellar mass of the spheroidal component (e.g., Kormendy & Ho 2013; Shankar et al. 2016). The Today it is commonly accepted that all massive galaxies host a su- existence of such relations is somewhat surprising given the many permassive black hole (SMBH) at their centres. Furthermore, there orders of magnitude difference in size between the black hole sphere is increasing evidence that the SMBHs somehow co-evolve with of influence and the bulk of the galaxy. This raises the questions their host galaxies as, for example, indicated by empirical scal- of how the feeding of the SMBH exactly works (e.g., Alexander & ing relations between the SMBH mass and galaxy properties, such Hickox 2012), and if there is significant feedback from the SMBH onto the host galaxies. The latter process is postulated by current cosmological simulations to suppress star formation and explain the ? E-mail: [email protected] © 2020 The Authors 2 D. Asmus et al. galaxy population as observed today in the nearby Universe (e.g., samples, e.g., after 70 month scanning time (hereafter B70 AGN Granato et al. 2004; Shankar et al. 2006; Lapi et al. 2006). sample; Koss et al. 2017; Ricci et al. 2017). The last decades of research have significantly increased our However, even the BAT AGN samples are restricted in two understanding of SMBH growth (see Netzer 2015 for a recent re- ways. First, the sensitivity of this selection method is relatively low view). We know that SMBHs grow through several phases over because of the low photon counts. This caveat results in relatively cosmic time, during which large amounts of matter are accreted. high flux limits, so that even relatively powerful AGN remain un- During its journey towards the event horizon, the material forms detected by BAT. Second and more importantly, even at such high 24 −2 an accretion disk which, due to the release of gravitational energy, energies, Compton-thick (CT) obscuration (NH > 1:5 · 10 cm ) emits large amounts of radiation, mostly in the ultraviolet (UV) extinguishes the intrinsic flux by factors of ten and larger, resulting which then is partly reprocessed by surrounding material and sec- in a detection bias against CT obscured AGN. This last point is a se- ondary processes. As a result, the galaxy nuclei appear as bright vere problem because the intrinsic fraction of CT-obscured AGN is compact sources, often outshining the rest of the galaxy. They are probably around ∼ 30% (e.g., Ricci et al. 2015; Lansbury et al. 2017; called active galactic nuclei (AGN). AGN are bright emitters across Georgantopoulos & Akylas 2019, Boorman et al., in prep.), and pos- most of the electromagnetic range and, thus, detectable throughout sibly even up 50% (Ananna et al. 2019; but see Gandhi et al. 2007). the entire visible Universe which allows us to directly trace SMBH Both caveats will be somewhat mitigated in the future with deeper growth over cosmic history. In addition, AGN can produce strong Swift/BAT maps although only slowly as the mission has already outflows which are prime candidates for the feedback onto the host reached more than eight years of total integration time. The newest galaxy postulated above. However, to robustly answer which pro- X-ray satellite, the Russian-German “Spectrum-Roentgen-Gamma” cesses are dominating the SMBH growth and the feedback, we (SRG) mission could allow for advance in this matter. It hosts two require a complete census of the AGN phenomenon. For example, telescopes which will perform a four-year all-sky survey at com- precise knowledge of the AGN number counts in the local Universe plementary X-ray energies, namely the extended ROentgen Survey would provide tight constraints on the duty cycle of AGN, radia- with an Imaging Telescope Array (eROSITA; Predehl et al. 2010; tive efficiencies and the luminosity and accretion rate distributions Merloni et al. 2012) operating at 0.2-10 keV and the Astronomi- (e.g., Martini & Weinberg 2001; Goulding et al. 2010; Shankar et al. cal Roentgen Telescope - X-ray Concentrator (ART-XC; Pavlinsky 2009, 2019). Such a census is very challenging to carry out. First of et al. 2011, 2018) operating at 4-30 keV. In terms of detecting AGN all, the accretion rates of SMBHs span a wide range from essentially with their X-ray emission described by a typical power-law, these zero up to values in excess of the Eddington limit. Therefore, AGN surveys are expected to be approximately ten times deeper than the span a huge range in luminosities from the nearly quiescent Galac- current Swift/BAT survey. Thus, these surveys are our best chance tic Centre, Sgr A∗, to the most powerful quasars roughly twelve to probe the local AGN population at sufficient depth, in particular orders of magnitude more luminous. Faint AGN are difficult to de- to detect (or place stringent constraints on) many of the still missing tect, in particular if they do not outshine their host galaxy at some CT AGN. wavelengths. Moreover, the majority of SMBH growth seems to be highly obscured from our lines of sight (e.g., Fabian 1999; Ueda et al. 2014; Buchner et al. 2015; Ricci et al. 2015). So what is the 1.2 Selecting AGN in the mid-infrared regime best, i.e., most efficient and least biased, way to find all the AGN? Our best chance to achieve this is certainly in the nearby Universe, Complementary to X-ray selection of AGN is selection in the mid- where the sensitivity and angular resolution of our instruments can infrared (MIR). About half of the primary emission from the ac- be used to their largest effect for finding and characterising even cretion disk is absorbed by dust, surrounding the AGN probably on highly obscured AGN. This is the ultimate goal of the new sur- parsec scales in a more or less coherent structure (see Almeida & vey presented here, the Local AGN Survey (LASr). Its design is Ricci 2017 and Hönig 2019 for recent reviews). As a result, this dust motivated by the following insights.
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