Towards a complete census of AGN in nearby Galaxies: a large population of optically unidentified AGN

By A. Goulding, D. M. Alexander. 2009

190 citations recorded by the source corpus.

Using Spitzer-infrared spectrograph (IRS) spectroscopy, we investigate the ubiquity of active galactic nuclei (AGN) in a complete (≈94 per cent), volume-limited sample of the most bolometrically luminous galaxies [L IR , 8-1000 μm ≥(0.3-20) × 10 10 L ⊙ ] to D < 15 Mpc. Our analyses are based on the detection of the high-excitation emission line [Ne v]λ14.32 μm (97.1 eV) to unambiguously identify AGN activity. We find that 17 of the 64 infrared (IR) bright galaxies in our sample host AGN activity (≈27+8/-6 per cent), ≥50 per cent of which are not identified as AGN using optical spectroscopy. The large AGN fraction indicates a tighter connection between AGN activity and IR luminosity for galaxies in the local Universe than previously found, potentially indicating a close association between AGN activity and star formation. The optically unidentified AGN span a wide range of galaxy type (S0-Ir) and are typically starburst-dominated systems hosting modest-luminosity AGN activity (L [Ne V] ≈ 10 37 -10 39 erg s -1 ). The non-identification of optical AGN signatures in the majority of these galaxies appears to be due to extinction towards the AGN, rather than intrinsically low-luminosity AGN activity; however, we note that the AGN optical signatures are diluted in some galaxies due to strong star formation activity. Examination of optical images shows that the optically unidentified AGN with evidence for extinction are hosted in either highly inclined galaxies or galaxies with dust lanes, indicating that obscuration of the AGN is not necessarily due to an obscuring torus. We therefore conclude that optical spectroscopic surveys miss approximately half of the AGN population simply due to extinction through the host galaxy.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/e9727e348a5efe948c34261f475f2275d84583a6

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Citations in the corpus

Defining the intrinsic AGN infrared spectral energy distribution and measuring its contribution to the infrared output of composite galaxies (2011, methodology): “Following the diagnostics presented in Goulding & Alexander (2009) and Tommasin et al. (2010), we quantify the contribution of the host galaxy to these MIR spectra using the equivalent widths of the 11.25µm PAH feature (hereafter, EW PAHλ11.”
A NEW DIAGNOSTIC OF ACTIVE GALACTIC NUCLEI: REVEALING HIGHLY ABSORBED SYSTEMS AT REDSHIFT >0.3 (2011, background): “…galaxy is viewed through a dust lane, AGN emissionline signatures such as [O iii]λ5007 can be weakened and further diluted with emission from peripheral star formation (Maiolino & Rieke 1995; Malkan et al. 1998; Goulding & Alexander 2009), causing the global signal to exhibit composite signatures.”
What drives the growth of black holes (2011, background): “…wavelengths and mid-IR spectroscopy or hard X-ray observations are required to unambiguously identify them (e.g., Ho, 2008; Satyapal et al., 2008; Goulding & Alexander, 2009; Koss et al., 2011): the presence of dust and star formation in the host galaxy often dilute or extinguish the optical AGN…”
THE NEXT GENERATION ATLAS OF QUASAR SPECTRAL ENERGY DISTRIBUTIONS FROM RADIO TO X-RAYS (2011, methodology): “These features have been investigated in detail in previous studies (e.g., Hao et al. 2005; Weedman et al. 2005; Dale et al. 2009; Goulding & Alexander 2009; Diamond-Stanic et al. 2009; Pereira-Santaella et al. 2010; Tommasin et al. 2010), and have been kept in our analyses.”
A CORRELATION BETWEEN STAR FORMATION RATE AND AVERAGE BLACK HOLE ACCRETION IN STAR-FORMING GALAXIES (2013, background): “…effectively identify obscured AGN at moderate redshift (Gorjian et al. 2008; Assef et al. 2010), since mid-IR wavelengths are not as strongly affected by obscuration as the optical or UV (e.g. Lacy et al. 2004; Stern et al. 2005; Donley et al. 2007; Hickox et al. 2007; Goulding & Alexander 2009).”
A CHANDRA PERSPECTIVE ON GALAXY-WIDE X-RAY BINARY EMISSION AND ITS CORRELATION WITH STAR FORMATION RATE AND STELLAR MASS: NEW RESULTS FROM LUMINOUS INFRARED GALAXIES (2010, methodology): “These data were analyzed following the methods outlined in Goulding & Alexander (2009).”
Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, background): “…in only one waveband cannot provide a complete census of AGNs in galaxy samples due to obscuration of the central source or contamination of the observed emission by the host galaxy (e.g. Satyapal et al. 2008; Goulding & Alexander 2009; Hickox et al. 2009; Donley et al. 2010; Juneau et al. 2013).”
Revisiting the Unified Model of Active Galactic Nuclei (2015, background): “In some cases, galactic extinction is so large that it can completely obscure the central AGN at optical wavelengths (Goulding & Alexander 2009).”
The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe (2014, unknown): “This advantage relative to [OIII] has been exploited by Satyapal et al. (2008, 2009) and Goulding & Alexander (2009) to identify examples of low-luminosity AGN in the nuclei of nearby late-type galaxies that were not recognized as AGN based on optical spectra that were dominated by regions of star…”
Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey (2017, methodology): “Mid-IR AGN identifications can be made either through the detection of high-ionization emission lines in mid-IR spectroscopy (e.g., Diamond-Stanic et al. 2009; Goulding & Alexander 2009), or through the establishment of the presence of an AGN-produced powerlaw continuum using mid-IR photometry.”