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In this paper, we investigate 2727 galaxies observed by MaNGA as of June 2016to develop spatially resolved techniques for identifying signatures of activegalactic nuclei (AGN). We identify 303 AGN candidates. The additional spatialdimension imposes challenges in identifying AGN due to contamination fromdiffuse ionized gas, extra-planar gas and photoionization by hot stars. We showthat the combination of spatially-resolved line diagnostic diagrams andadditional cuts on H$\alpha$ surface brighness and H$\alpha$ equivalent widthcan distinguish between AGN-like signatures and high-metallicity galaxies withLINER-like spectra. Low mass galaxies with high specific star formation ratesare particularly difficult to diagnose and routinely show diagnostic lineratios outside of the standard star-formation locus. We develop a newdiagnostic -- the distance from the standard diagnostic line in the line-ratiosspace -- to evaluate the significance of the deviation from the star-formationlocus. We find 173 galaxies that would not have been selected as AGN candidatesbased on single-fibre spectral measurements but exhibit photoionizationsignatures suggestive of AGN activity in the MaNGA resolved observations,underscoring the power of large integral field unit (IFU) surveys. A completecensus of these new AGN candidates is necessary to understand their nature andprobe the complex co-evolution of supermassive black holes and their hosts.

SDSS-IV MaNGA: Identification of active galactic nuclei in optical integral field unit surveys