Evidence for Black Holes in Green Peas from WISE colors and variability

We explore the presence of active galactic nuclei (AGN)/black hole (BH) in Green Pea galaxies (GPs), motivated by the presence of high ionization emission lines such as HeII and [NeIII] in their optical spectra. In order to identify AGN candidates, we used mid-infrared (MIR) photometric observations from the all-sky Wide-field Infrared Survey Explorer (WISE) mission for a sample of 516 GPs. We select 58 GPs as candidate AGN based on a stringent 3-band WISE color diagnostic. Using multi-epoch photometry of W1 and W2 bands from the WISE/NEOWISE-R observations, we find 38 GPs showing significant variability in both the WISE bands. Four of these were selected as AGN by the WISE 3-band color diagnostic as well. Interestingly, we find a high fraction of MIR variable sources among GPs which demonstrates the uniqueness and importance of studying these extreme objects. Through this work, we demonstrate that photometric variability is a promising tool to select AGN that may be missed by other selection techniques (including optical emission-line ratios and X-ray emission) in star-formation dominated, low-mass, low-metallicity galaxies.