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Are Active Galactic Nuclei in Post-starburst Galaxies Driving the Change or Along for the Ride?

Lanz, Lauranne and Stepanoff, Sofia and Hickox, Ryan C. and Alatalo, Katherine and French, K. Decker and Rowlands, Kate and Nyland, Kristina and Appleton, Philip N. and Lacy, Mark and Medling, Anne and Mulchaey, John S. and Sazonova, Elizaveta and Urry, Claudia Megan (2022) Are Active Galactic Nuclei in Post-starburst Galaxies Driving the Change or Along for the Ride? Astrophysical Journal, 935 (1). Art. No. 29. ISSN 0004-637X. doi:10.3847/1538-4357/ac7d56.

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We present an analysis of 10 ks snapshot Chandra observations of 12 shocked post-starburst galaxies, which provide a window into the unresolved question of active galactic nuclei (AGN) activity in post-starburst galaxies and its role in the transition of galaxies from active star formation to quiescence. While seven of the 12 galaxies have statistically significant detections (with two more marginal detections), the brightest only obtained 10 photons. Given the wide variety of hardness ratios in this sample, we chose to pursue a forward-modeling approach to constrain the intrinsic luminosity and obscuration of these galaxies, rather than stacking. We constrain the intrinsic luminosity of obscured power laws based on the total number of counts and spectral shape, itself mostly set by the obscuration, with hardness ratios consistent with the data. We also tested thermal models. While all the galaxies have power-law models consistent with their observations, a third of the galaxies are better fit as an obscured power law and another third are better fit as thermal emission. If these post-starburst galaxies, early in their transition, contain AGNs, then these are mostly confined to lower obscuration (N_H ≤ 10²³ cm⁻²) and lower luminosity (L₂₋₁₀ ₖₑᵥ ≤ 10⁴² erg s⁻¹). Two galaxies, however, are clearly best fit as significantly obscured AGNs. At least half of this sample shows evidence of at least low-luminosity AGN activity, though none could radiatively drive out the remaining molecular gas reservoirs. Therefore, these AGNs are more likely along for the ride, having been fed gas by the same processes driving the transition.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Lanz, Lauranne0000-0002-3249-8224
Stepanoff, Sofia0000-0002-7850-7093
Hickox, Ryan C.0000-0003-1468-9526
Alatalo, Katherine0000-0002-4261-2326
French, K. Decker0000-0002-4235-7337
Rowlands, Kate0000-0001-7883-8434
Nyland, Kristina0000-0003-1991-370X
Appleton, Philip N.0000-0002-7607-8766
Lacy, Mark0000-0002-3032-1783
Medling, Anne0000-0001-7421-2944
Mulchaey, John S.0000-0003-2083-5569
Sazonova, Elizaveta0000-0001-6245-5121
Urry, Claudia Megan0000-0002-0745-9792
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 August 25; revised 2022 June 20; accepted 2022 June 28; published 2022 August 10. L.L. thanks Alexander Nazarov for his contributions in helping to lay the groundwork for this analysis and Michael Ochs for useful discussions on Bayesian statistics. The scientific results reported in this article are based on observations made by the Chandra X-Ray Observatory. Support for this work was provided by the National Aeronautics and Space Administration through Chandra Award No. GO7-18093A issued by the Chandra X-Ray Observatory Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of the National Aeronautics Space Administration (NASA), under contract NAS8-03060. L.L. and S.S. also acknowledge support from NASA through grant No. 80NSSC20K0050. Basic research in radio astronomy at the U.S. Naval Research Laboratory is supported by 6.1 Base Funding. A.M.M. acknowledges support from the National Science Foundation under grant No. 2009416. Facility: CXO - Chandra X-ray Observatory satellite. Software: Sherpa (Freeman et al. 2001; Doe et al. 2007).
Funding AgencyGrant Number
Naval Research Laboratory6.1 Base funding
Subject Keywords:Post-starburst galaxies; Active galactic nuclei; Low-luminosity active galactic nuclei; Galaxy evolution; X-ray astronomy
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Post-starburst galaxies (2176); Active galactic nuclei (16); Lowluminosity active galactic nuclei (2033); Galaxy evolution (594); X-ray astronomy (1810)
Record Number:CaltechAUTHORS:20220811-457373000
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Official Citation:Lauranne Lanz et al 2022 ApJ 935 29
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:116237
Deposited By: George Porter
Deposited On:12 Aug 2022 02:10
Last Modified:12 Aug 2022 02:10

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