2024/08/01 by Aravindan, Archana, Canalizo, Gabriela, Secrest, Nathan +2
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2408.00666
Detecting active black holes in dwarf galaxies has proven to be a challenge due to their small size and weak electromagnetic signatures. Mid-infrared variability has emerged as a promising tool that can be used to detect active low-mass black holes in dwarf galaxies. We analyzed 10.4 years of photometry from the ALLWISE/NEOWISE multi-epoch catalogs, identifying 25 objects with AGN-like variability. Independent confirmation of AGN activity was found in 68% of these objects using optical and near-infrared diagnostics. Notably, we discovered a near-infrared coronal line [S IX] λ 1.252 μm in J1205, the galaxy with the lowest stellar mass (log M* = 7.5 M\odot) and low metallicity (12 + log(O/H) = 7.46) in our sample. Additionally, we found broad Paα potentially from the BLR in two targets, and their implied black hole masses are consistent with black hole-stellar mass relations. Comparing non-variable galaxies with similar stellar masses and WISE W1-W2 colors, we found no clear trends between variability and large-scale galaxy properties. However, we found that AGN activity likely causes redder W1-W2 colors in variable targets, while for the non-variable galaxies, the contribution stems from strong star formation activity. A high incidence of optical broad lines was also observed in variable targets. Our results suggest that mid-infrared variability is an effective method for detecting AGN activity in low-mass galaxies and can help uncover a larger sample of active low-mass (< 106 M\odot) black holes in the universe.