Crossing the line: How often are AGN found in the star-forming region of the BPT diagram?
Abstract
In this work, we investigate how often do AGN end up being classified as star-forming galaxies by the Baldwin-Phillips-Terlevich (BPT) diagram. We identify 323 true AGN by comparing X-ray luminosities from deep observations from 3XMM to star formation rates from GALEX-SDSS-WISE-Legacy Catalog. Nearly 11% of these X-ray AGN are optically classified as BPT star-forming galaxies. We find that star-formation dilution is the most probable cause of misclassification for ~80% of these X-ray AGN. The remaining ~20% have low star formation rates and the optical signatures consistent with inherently weak accretion. We find that the fraction of X-ray AGN in the base of the star-forming branch of the BPT diagram is 4.6%. At the tip of the star-forming branch, the fraction of X-ray AGN is lower than 0.2%. These results suggest that selection of galaxies via the BPT diagram can provide a reasonably clean (>95%) sample of star-forming galaxies.
- Publication:
-
American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23310603A