| Title: |
RESOLVE and ECO: Finding Low-Metallicity $z\sim0$ Dwarf AGN Candidates Using Optimized Emission-Line Diagnostics |
| Authors: |
Polimera, Mugdha S.; Kannappan, Sheila J.; Richardson, Chris T.; Bittner, Ashley S.; Ferguson, Carlynn; Moffett, Amanda J.; Eckert, Kathleen D.; Bellovary, Jillian M.; Norris, Mark A. |
| Publication Year: |
2022 |
| Collection: |
Astrophysics |
| Subject Terms: |
Astrophysics - Astrophysics of Galaxies |
| Description: |
Existing star-forming vs. active galactic nucleus (AGN) classification schemes using optical emission-line diagnostics mostly fail for low-metallicity and/or highly star-forming galaxies, missing AGN in typical $z\sim0$ dwarfs. To recover AGN in dwarfs with strong emission lines (SELs), we present a classification scheme optimizing the use of existing optical diagnostics. We use SDSS emission-line catalogs overlapping the volume- and mass-limited RESOLVE and ECO surveys to determine the AGN percentage in SEL dwarfs. Our photoionization grids show that the [O III]/H$\beta$ versus [S II]/H$\alpha$ diagram (SII plot) and [O III]/H$\beta$ versus [O I]/H$\alpha$ diagram (OI plot) are less metallicity sensitive and more successful in identifying dwarf AGN than the popular [O III]/H$\beta$ versus [N II]/H$\alpha$ diagnostic (NII plot or "BPT diagram"). We identify a new category of "star-forming AGN" (SF-AGN) classified as star-forming by the NII plot but as AGN by the SII and/or OI plots. Including SF-AGN, we find the $z\sim0$ AGN percentage in dwarfs with SELs to be $\sim$3-16\%, far exceeding most previous optical estimates ($\sim$1\%). The large range in our dwarf AGN percentage reflects differences in spectral fitting methodologies between catalogs. The highly complete nature of RESOLVE and ECO allows us to normalize strong emission-line galaxy statistics to the full galaxy population, reducing the dwarf AGN percentage to $\sim$0.6-3.0\%. The newly identified SF-AGN are mostly gas-rich dwarfs with halo mass $ < 10^{11.5} M_\odot$, where highly efficient cosmic gas accretion is expected. Almost all SF-AGN also have low metallicities (Z $\lesssim 0.4$ Z$_\odot$), demonstrating the advantage of our method.; Comment: 31 pages, 16 figures, 3 tables. Accepted by ApJ on April 3 2022 |
| Document Type: |
Working Paper |
| DOI: |
10.3847/1538-4357/ac6595 |
| Access URL: |
http://arxiv.org/abs/2204.03633 |
| Accession Number: |
edsarx.2204.03633 |
| Database: |
arXiv |