Multi-epoch spectroscopy of dwarf galaxies with AGN signatures: identifying sources with persistent broad Hα emission

Journal Article · Tue Sep 20 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/829/1/57· OSTI ID:22868656

Baldassare, Vivienne F.; Reines, Amy E.; Gallo, Elena ^[1]; Greene, Jenny E. ^[2]; Graur, Or ^[3]; Geha, Marla ^[4]; Hainline, Kevin ^[5]; Carroll, Christopher M.; Hickox, Ryan C. ^[6]

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1. Department of Astronomy, University of Michigan, Ann Arbor, MI 48109 (United States)
2. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
3. Center for Cosmology and Particle Physics, New York University, New York, NY 10003 (United States)
4. Department of Astronomy, Yale University, New Haven, CT 06520 (United States)
5. Steward Observatory, Tucson, AZ 85721 (United States)
6. Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755 (United States)

We use time-domain optical spectroscopy to distinguish between broad emission lines powered by accreting black holes (BHs) and stellar processes (i.e., supernovae) for 16 galaxies identified as active galactic nucleus (AGN) candidates by Reines et al (2013). Our study is primarily focused on those objects with narrow emission line ratios dominated by star formation, for which the origin of the broad Hα emission was unclear. Based on follow-up spectroscopy, we find that the broad Hα emission has faded or was ambiguous for all of the star-forming objects (14/16), over baselines ranging from 5–14 years, suggesting a transient stellar process was responsible for the broad emission in previous Sloan Digital Sky Survey observations. For the two objects in our follow-up sample with narrow-line AGN signatures (RGG 9 and RGG 119), we find persistent broad Hα emission consistent with an AGN origin. Additionally, we use high spectral resolution observations to measure stellar velocity dispersions for 15 objects in the Reines et al. (2013) sample, all with narrow-line ratios indicating the presence of an AGN. Stellar masses range from ∼5×10{sup 8} to 3×10{sup 9} M {sub ⊙}, and we measure σ{sub ∗} in the range of 28--71 km s{sup −1}. These σ{sub ∗} correspond to some of the lowest-mass galaxies with optical signatures of AGN activity. We show that RGG 119, the one object that has both a measured σ{sub ∗} and persistent broad Hα emission, falls near the extrapolation of the M{sub BH}−σ{sub ⋆} relation to the low-mass end.

• OSTI ID: 22868656
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 829; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
BLACK HOLES
DISPERSIONS
DWARF STARS
EMISSION
EXTRAPOLATION
GALAXIES
MASS
NUCLEI
QUASARS
RESOLUTION
SPECTROSCOPY
SUPERNOVAE