News
Central Black Hole Detections Jump near Milky Way Mass
Posted January 8, 2025
RESOLVE/ECO team research to be published in the Astrophysical Journal reveals that active galactic nuclei (AGN, or growing massive black holes) are roughly five times more common in mid-size galaxies like the Milky Way than in dwarf galaxies. Using multiple optical and mid-infrared techniques to cut through the glare of star formation, we found AGN in 2-5% of dwarf galaxies, exceeding most prior estimates. Nonetheless, AGN jumped sharply to 16-27% in the transitional mass range between dwarfs and giants, which includes the Milky Way at its upper end. The abstract of our submitted and favorably refereed paper is below, and you can follow these links to check out the American Astronomical Society poster and press release on this work.
A Comprehensive AGN Inventory for the Dwarf-Dominated RESOLVE and ECO Surveys: Mass-Dependent AGN Types and Occupation Fractions
Polimera, Mugdha S., Kannappan, Sheila J., Richardson, Chris T., Stark, David V., Eckert, Kathleen D., Jarrett, Thomas H., Carr, Derrick S., Hutchens, Zackary L., Bellovary, Jillian M., and Norris, Mark A.
We catalog Active Galactic Nuclei (AGN) in the volume- and mass-limited RESOLVE and ECO surveys using (i) the BPT plot with standard and alternate demarcations, (ii) the BPT plot and VO plots (using [OI] or [SII]) to find "SF-AGN" with mixed star-forming and AGN classifications, and (iii) mid-IR WISE color selection. Dividing RESOLVE+ECO into dwarf, transitional, and giant galaxies by baryonic mass, we find AGN occupation fractions of 2-5%, 16-27%, and 20-48%, respectively, computed relative to all galaxies in each mass range including those not searchable for AGN. These percentage ranges encompass large systematics between crossmatched emission-line measurements from different SDSS catalogs. Stellar-mass divisions yield similar results. Adding (incomplete) archival X-ray/broadline AGN detections, the dwarf AGN occupation fraction reaches 3-6. WISE AGN are detected in <1% of galaxies at all masses with optimized WISE photometry; we show that standard catalog photometry yields high rates of both false positives and false negatives. AGN demographics shift with mass due to correlations with gas content, star formation, and group environment, forming a continuum: SF-AGN at the high-SF end, then "Bonus AGN" (defined by alternate literature BPT demarcations), then Composites, then Conventional AGN at the low-SF end. Typical (metal-poor, star-forming) dwarfs most often host SF-AGN, whereas typical transitional galaxies most often host Bonus AGN and Composites. We release homogenized SDSS line measurements, reprocessed WISE data, and UV+mid-IR star formation rates for RESOLVE and ECO.