Why Post-starburst Galaxies Are Now Quiescent

K. Decker French, Ann I Zabludoff, Ilsang Yoon, Yancy L Shirley, Yujin Yang, Adam Smercina, J. D. Smith, Desika Narayanan

Research output: Contribution to journalArticle

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Abstract

Post-starburst or "E + A" galaxies are rapidly transitioning from star-forming to quiescence. While the current star formation rate (SFR) of post-starbursts is already at the level of early-type galaxies, we recently discovered that many have large CO-traced molecular gas reservoirs consistent with normal star-forming galaxies. These observations raise the question of why these galaxies have such low SFRs. Here we present an ALMA search for the denser gas traced by HCN (1-0) and HCO+ (1-0) in two CO-luminous, quiescent post-starburst galaxies. Intriguingly, we fail to detect either molecule. The upper limits are consistent with the low SFRs and with early-type galaxies. The HCN/CO luminosity ratio upper limits are low compared to star-forming and even many early-type galaxies. This implied low dense gas mass fraction explains the low SFRs relative to the CO-traced molecular gas and suggests that the state of the gas in post-starburst galaxies is unusual, with some mechanism inhibiting its collapse to denser states. We conclude that post-starbursts galaxies are now quiescent because little dense gas is available, in contrast to the significant CO-traced lower density gas reservoirs that still remain.

Original languageEnglish (US)
Article number123
JournalAstrophysical Journal
Volume861
Issue number2
DOIs
StatePublished - Jul 10 2018

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starburst galaxies
galaxies
gas
molecular gases
gases
stars
rarefied gases
star formation rate
luminosity
molecules
gas reservoir

Keywords

  • galaxies: evolution
  • galaxies: ISM

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

French, K. D., Zabludoff, A. I., Yoon, I., Shirley, Y. L., Yang, Y., Smercina, A., ... Narayanan, D. (2018). Why Post-starburst Galaxies Are Now Quiescent. Astrophysical Journal, 861(2), [123]. https://doi.org/10.3847/1538-4357/aac8de

Why Post-starburst Galaxies Are Now Quiescent. / French, K. Decker; Zabludoff, Ann I; Yoon, Ilsang; Shirley, Yancy L; Yang, Yujin; Smercina, Adam; Smith, J. D.; Narayanan, Desika.

In: Astrophysical Journal, Vol. 861, No. 2, 123, 10.07.2018.

Research output: Contribution to journalArticle

French, KD, Zabludoff, AI, Yoon, I, Shirley, YL, Yang, Y, Smercina, A, Smith, JD & Narayanan, D 2018, 'Why Post-starburst Galaxies Are Now Quiescent', Astrophysical Journal, vol. 861, no. 2, 123. https://doi.org/10.3847/1538-4357/aac8de
French, K. Decker ; Zabludoff, Ann I ; Yoon, Ilsang ; Shirley, Yancy L ; Yang, Yujin ; Smercina, Adam ; Smith, J. D. ; Narayanan, Desika. / Why Post-starburst Galaxies Are Now Quiescent. In: Astrophysical Journal. 2018 ; Vol. 861, No. 2.
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