CaltechAUTHORS
Published October 20, 2019 | Version Submitted + Published
Journal Article Open

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

Creators

  • 1. ROR icon Yale University
  • 2. ROR icon University of California, Davis
  • 3. ROR icon California Institute of Technology
  • 4. ROR icon Carnegie Observatories
  • 5. ROR icon University of California, Berkeley

Abstract

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.

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.

Attached Files

Published - Dickey_2019_ApJ_884_180.pdf

Submitted - 1902.01401.pdf

Files

1902.01401.pdf

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Additional details

Identifiers

Eprint ID
99427
Resolver ID
CaltechAUTHORS:20191023-160058903

Related works

Describes
https://arxiv.org/abs/1902.01401 (URL)

Funding

NSF
AST-1517422
Howard Hughes Medical Institute (HHMI)
Caltech-Carnegie Fellowship
Caltech Moore Center for Theoretical Cosmology and Physics
NASA
80NSSC18K1097
NASA Hubble Fellowship
HST GO-14734
NASA Hubble Fellowship
AR-15057
Space Telescope Science Institute
NSF Graduate Research Fellowship

Dates

Created
2019-10-23
Created from EPrint's datestamp field
Updated
2023-01-05
Created from EPrint's last_modified field

Caltech Custom Metadata

Caltech groups
TAPIR , Moore Center for Theoretical Cosmology and Physics