Active Galactic Nuclei from HeII: a more complete census of AGN in SDSS galaxies yields a new population of low-luminosity AGN in highly star-forming galaxies

Abstract

In order to perform a more complete census of active galactic nuclei (AGN) in the local Universe, we investigate the use of the HeII~$\lambda 4685$ emission line diagnostic diagram by Shirazi & Brinchmann (2012) in addition to the standard methods based on other optical emission lines. The He II based diagnostics is more sensitive to AGN ionization in the presence of strong star formation than conventional line diagnostics. We survey a magnitude-limited sample of 63,915 galaxies from the Sloan Digital Sky Survey Data Release 7 at $0.02<z<0.05$ and use both the conventional BPT emission line diagnostic diagrams, as well as the HeII diagram to identify AGN. In this sample, 1,075 galaxies are selected as AGN using the BPT diagram, while an additional 234 galaxies are identified as AGN using the HeII diagnostic diagram, representing a 22% increase of AGN in the parent galaxy sample. We explore the host galaxy properties of these new HeII selected AGN candidates and find that they are most common in star-forming galaxies on the blue cloud and on the main sequence where ionization from star-formation is most likely to mask AGN emission in the BPT lines. We note in particular a high HeII AGN fraction in galaxies above the high-mass end of the main sequence where quenching is expected to occur. We use archival Chandra observations to confirm the AGN nature of candidates selected through HeII based diagnostic. Finally, we discuss how this technique can help inform galaxy/black hole co-evolution scenarios.

Accepted for publication in MNRAS

References in corpus (21)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Mass and environment as drivers of galaxy evolution in SDSS and zCOSMOS and the origin of the Schechter function
• UV Star Formation Rates in the Local Universe
• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: I. Galaxy Mergers & Quasar Activity
• The Co-Evolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe
• Strangulation as the primary mechanism for shutting down star formation in galaxies
• Star formation in AEGIS field galaxies since z=1.1 . Staged galaxy formation, and a model of mass-dependent gas exhaustion
• A Cosmological Framework for the Co-Evolution of Quasars, Supermassive Black Holes, and Elliptical Galaxies: II. Formation of Red Ellipticals
• Cosmic X-ray Surveys of Distant Active Galaxies: The Demographics, Physics, and Ecology of Growing Supermassive Black Holes
• AEGIS: The color-magnitude relation for X-ray selected AGN
• A Turnover in the Galaxy Main Sequence of Star Formation at $M_{\ast }\sim 10^{10}{M}_{\odot }$ for Redshifts $z<1.3$
• AGN Emission Line Diagnostics and the Mass-Metallicity Relation up to Redshift z~2: the Impact of Selection Effects and Evolution
• The Evolution of AGN Host Galaxies: From Blue to Red and the Influence of Large-Scale Structures
• Galaxy And Mass Assembly: Deconstructing Bimodality - I. Red ones and blue ones
• Two Conditions for Galaxy Quenching: Compact Centres and Massive Haloes
• A New Catalogue of Type 1 AGN and its Implication on the AGN Unified Model
• The role of AGN in the colour transformation of galaxies at redshifts z~1
• Quenching of Star Formation in SDSS Groups: Centrals, Satellites, and Galactic Conformity
• Ongoing Formation of Bulges and Black Holes in the Local Universe: New Insights from GALEX
• The Accuracy of Morphological Decomposition of Active Galactic Nucleus Host Galaxies
• Star formation and quenching among the most massive galaxies at z~1.7

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