Towards a More Complete Optical Census of Active Galactic Nuclei, Via Spatially-Resolved Spectroscopy

Abstract

While emission-line flux ratio diagnostics are the most common technique for identifying active galactic nuclei (AGNs) in optical spectra, applying this approach to single fiber spectra of galaxies can omit entire subpopulations of AGNs. Here, we use spatially resolved spectroscopy from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to construct a sample of 10 galaxies where Baldwin-Philips-Terlevich line flux ratio diagnostics classify each galaxy's central $3^{\prime \prime }$ spectrum as LINER or star forming, while $>10\%$ of the spaxels in the galaxy's MaNGA footprint are classified as Seyfert. We obtain Chandra observations of these 10 galaxies with off-nuclear Seyfert regions to determine whether AGNs are actually present in them. Our main result is that 7-10 (depending on strictness of criteria) of the galaxies host one or more X-ray AGNs, even though none of them were classified as AGNs based on their single-fiber optical spectra. We find that these AGNs were not identified in the single-fiber spectra because they are AGNs in the nuclei of companion galaxies, low luminosity AGNs, dust obscured AGNs, and/or flickering AGNs. In summary, we find that off-nuclear AGN signatures may increase the number of known AGNs by a factor of two over what conventional single nuclear fiber spectra identify. Our results show that spatially resolved spectroscopy can be leveraged to reveal a more complete census of AGNs that are traditionally missed by single fiber spectra.

20 pages, 5 figures, accepted for publication in ApJ

References in corpus (21)

• The Host Galaxies and Classification of Active Galactic Nuclei
• Overview of the SDSS-IV MaNGA Survey: Mapping Nearby Galaxies at Apache Point Observatory
• The MAPPINGS III Library of Fast Radiative Shock Models
• Active Galactic Nuclei: what's in a name?
• The MaNGA Integral Field Unit Fiber Feed System for the Sloan 2.5 m Telescope
• The Data Reduction Pipeline for the SDSS-IV MaNGA IFU Galaxy Survey
• The SDSS-IV MaNGA Sample: Design, Optimization, and Usage Considerations
• SDSS-IV MaNGA IFS Galaxy Survey --- Survey Design, Execution, and Initial Data Quality
• The WISE AGN Catalog
• The SAMI Galaxy Survey: Shocks and Outflows in a normal star-forming galaxy
• The X-Ray to Mid-Infrared Relation of AGN at High Luminosity
• A New Catalogue of Type 1 AGN and its Implication on the AGN Unified Model
• Hidden AGN in dwarf galaxies revealed by MaNGA: light echoes, off-nuclear wanderers, and a new broad-line AGN
• HST Imaging of Fading AGN Candidates I: Host-Galaxy Properties and Origin of the Extended Gas
• SDSS-IV MaNGA: Identification of active galactic nuclei in optical integral field unit surveys
• The first 62 AGN observed with SDSS-IV MaNGA - I: their characterization and definition of a control sample
• Discovery of a dual active galactic nucleus with ~ 8 kpc separation
• Chemical abundances in Seyfert galaxies -- V. The discovery of shocked emission outside the AGN ionization axis
• An Active Galactic Nucleus Caught in the Act of Turning Off and On
• Observational Constraints on Correlated Star Formation and Active Galactic Nuclei in Late-Stage Galaxy Mergers
• Shocks and Spatially Offset Active Galactic Nuclei Produce Velocity Offsets in Emission Lines