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Published July 1, 2017 | Published
Journal Article Open

Welcome to the Twilight Zone: The Mid-infrared Properties of Post-starburst Galaxies

Abstract

We investigate the optical and Wide-field Survey Explorer (WISE) colors of "E+A" identified post-starburst galaxies, including a deep analysis of 190 post-starbursts detected in the 2 μm All Sky Survey Extended Source Catalog. The post-starburst galaxies appear in both the optical green valley and the WISE Infrared Transition Zone. Furthermore, we find that post-starbursts occupy a distinct region of [3.4]–[4.6] versus [4.6]–[12] WISE colors, enabling the identification of this class of transitioning galaxies through the use of broadband photometric criteria alone. We have investigated possible causes for the WISE colors of post-starbursts by constructing a composite spectral energy distribution (SED), finding that the mid-infrared (4–12 μm) properties of post-starbursts are consistent with either 11.3 μm polycyclic aromatic hydrocarbon emission, or thermally pulsating asymptotic giant branch (TP-AGB) and post-AGB stars. The composite SED of extended post-starburst galaxies with 22 μm emission detected with signal-to-noise ratio ⩾3 requires a hot dust component to produce their observed rising mid-infrared SED between 12 and 22 μm. The composite SED of WISE 22 μm non-detections (S/N < 3), created by stacking 22 μm images, is also flat, requiring a hot dust component. The most likely source of the mid-infrared emission of these E+A galaxies is a buried active galactic nucleus (AGN). The inferred upper limits to the Eddington ratios of post-starbursts are 10^(−2)–10^(−4), with an average of 10^(−3). This suggests that AGNs are not radiatively dominant in these systems. This could mean that including selections capable of identifying AGNs as part of a search for transitioning and post-starburst galaxies would create a more complete census of the transition pathways taken as a galaxy quenches its star formation.

Additional Information

© 2017 American Astronomical Society. Received 2016 July 30. Accepted 2017 May 11. Published 2017 June 26. K.A. thanks R. Peletier for useful discussions as this manuscript was being prepared, as well as the anonymous referee for excellent suggestions that strengthened the manuscript. Support for K.A. is provided by NASA through Hubble Fellowship grant #HST-HF2-51352.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. P.N.A. is partially supported by funding through Herschel, a European Space Agency Cornerstone Mission with significant participation by NASA, through an award issued by JPL/Caltech. T.B. would like to acknowledge support from the CONACyT Research Fellowships program. S.L.C. was supported by ALMA-CONICYT program 31110020. J.F.B. acknowledges support from grant AYA2016-77237-C3-1-P from the Spanish Ministry of Economy and Competitiveness (MINECO). L.L. acknowledges support for this work provided by NASA through an award issued by JPL/Caltech. K.N. acknowledges support from NASA through the Spitzer Space Telescope. L.J.K. and A.M.M. acknowledge the support of the Australian Research Council (ARC) through Discovery project DP130103925. L.C. received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n 312725. Support for A.M.M. is provided by NASA through Hubble Fellowship grant #HST-HF2-51377 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. Facilities: Sloan, WISE.

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August 21, 2023
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