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AGN All the Way Down? AGN-like Line Ratios Are Common in the Lowest-mass Isolated Quiescent Galaxies

Dickey, Claire Mackay and Geha, Marla and Wetzel, Andrew and El-Badry, Kareem (2019) AGN All the Way Down? AGN-like Line Ratios Are Common in the Lowest-mass Isolated Quiescent Galaxies. Astrophysical Journal, 884 (2). Art. No. 180. ISSN 1538-4357. doi:10.3847/1538-4357/ab3220.

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We investigate the lowest-mass quiescent galaxies known to exist in isolated environments (M* = 10^(9.0-9.5) M⊙); 1.5 Mpc from a more massive galaxy). This population may represent the lowest stellar mass galaxies in which internal feedback quenches galaxy-wide star formation. We present a Keck/Echelle Spectrograph and Imager long-slit spectroscopy for 27 isolated galaxies in this regime (20 quiescent galaxies and 7 star-forming galaxies). We measure emission line strengths as a function of radius and place galaxies on the Baldwin–Phillips–Terlevich (BPT) diagram. Remarkably, 16 of 20 quiescent galaxies in our sample host central active galactic nucleus (AGN)-like line ratios. Only five of these quiescent galaxies were identified as AGN-like in the Sloan Digital Sky Survey due to a lower spatial resolution and signal-to-noise ratio. We find that many of the quiescent galaxies in our sample have spatially extended emission across the non-star-forming regions of BPT-space. While quenched galaxies in denser environments in this mass range often show no evidence for AGN activity, a significant fraction of quiescent galaxies in isolation host AGNs despite their overall passive appearances.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Dickey, Claire Mackay0000-0002-1081-3991
Geha, Marla0000-0002-7007-9725
Wetzel, Andrew0000-0003-0603-8942
El-Badry, Kareem0000-0002-6871-1752
Additional Information:© 2019 The American Astronomical Society. 2019 February 1; revised 2019 July 9; accepted 2019 July 13; published 2019 October 23. We thank the anonymous referee for their insightful feedback which has strengthened the paper. C.M.D. thanks Jenny Greene, Vivienne Baldassare, and Michael Tremmel for their helpful comments on this work. M.G. acknowledges support from the National Science Foundation under AST grant No. 1517422 and the Howard Hughes Medical Institute (HHMI) Professors Program. A.W. is supported by a Caltech-Carnegie Fellowship, in part through the Moore Center for Theoretical Cosmology and Physics at Caltech, and by NASA, through ATP grant 80NSSC18K1097 and HST GO-14734 and AR-15057 from STScI. K.E.B. acknowledges support from an NSF graduate research fellowship.
Group:TAPIR, Moore Center for Theoretical Cosmology and Physics
Funding AgencyGrant Number
Howard Hughes Medical Institute (HHMI)UNSPECIFIED
Caltech-Carnegie FellowshipUNSPECIFIED
Caltech Moore Center for Theoretical Cosmology and PhysicsUNSPECIFIED
NASA Hubble FellowshipHST GO-14734
NASA Hubble FellowshipAR-15057
Space Telescope Science InstituteUNSPECIFIED
NSF Graduate Research FellowshipUNSPECIFIED
Subject Keywords:galaxies: active – galaxies: dwarf – galaxies: evolution
Issue or Number:2
Record Number:CaltechAUTHORS:20191023-160058903
Persistent URL:
Official Citation:Claire Mackay Dickey et al 2019 ApJ 884 180
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:99427
Deposited By: Tony Diaz
Deposited On:23 Oct 2019 23:14
Last Modified:05 Jan 2023 22:44

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