Discovery of large molecular gas reservoirs in post-starburst galaxies

K. Decker French, Yujin Yang, Ann I Zabludoff, Desika Narayanan, Yancy L Shirley, Fabian Walter, John David Smith, Christy A. Tremonti

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

Post-starburst (or "E+A") galaxies are characterized by low Hα emission and strong Balmer absorption, suggesting a recent starburst, but little current star formation. Although many of these galaxies show evidence of recent mergers, the mechanism for ending the starburst is not yet understood. To study the fate of the molecular gas, we search for CO(1-0) and (2-1) emission with the IRAM 30 m and SMT 10 m telescopes in 32 nearby (0.01 < z < 0.12) post-starburst galaxies drawn from the Sloan Digital Sky Survey. We detect CO in 17 (53%). Using CO as a tracer for molecular hydrogen, and a Galactic conversion factor, we obtain molecular gas masses of M(H2) = 108.6-109.8 M and molecular gas mass to stellar mass fractions of 10-2-10-0.5, comparable to those of star-forming galaxies. The large amounts of molecular gas rule out complete gas consumption, expulsion, or starvation as the primary mechanism that ends the starburst in these galaxies. The upper limits on M(H2) for the 15 undetected galaxies range from 107.7 M to 109.7 M, with the median more consistent with early-type galaxies than with star-forming galaxies. Upper limits on the post-starburst star formation rates (SFRs) are lower by 10 × than for star-forming galaxies with the same M(H2). We also compare the molecular gas surface densities () to upper limits on the SFR surface densities (ΣSFR), finding a significant offset, with lower ΣSFR for a given than is typical for star-forming galaxies. This offset from the Kennicutt-Schmidt relation suggests that post-starburst galaxies have lower star formation efficiency, a low CO-to-H2 conversion factor characteristic of ultraluminous infrared galaxies, and/or a bottom-heavy initial mass function, although uncertainties in the rate and distribution of current star formation remain.

Original languageEnglish (US)
Article number1
JournalAstrophysical Journal
Volume801
Issue number1
DOIs
StatePublished - Mar 1 2015

Fingerprint

starburst galaxies
molecular gases
galaxies
gas
star formation rate
star formation
stars
starvation
merger
gas reservoir
tracer
rate
expulsion
hydrogen
stellar mass
gases
tracers
telescopes

Keywords

  • galaxies: evolution
  • radio lines: galaxies

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Discovery of large molecular gas reservoirs in post-starburst galaxies. / French, K. Decker; Yang, Yujin; Zabludoff, Ann I; Narayanan, Desika; Shirley, Yancy L; Walter, Fabian; Smith, John David; Tremonti, Christy A.

In: Astrophysical Journal, Vol. 801, No. 1, 1, 01.03.2015.

Research output: Contribution to journalArticle

French, K. Decker ; Yang, Yujin ; Zabludoff, Ann I ; Narayanan, Desika ; Shirley, Yancy L ; Walter, Fabian ; Smith, John David ; Tremonti, Christy A. / Discovery of large molecular gas reservoirs in post-starburst galaxies. In: Astrophysical Journal. 2015 ; Vol. 801, No. 1.
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AU - Yang, Yujin

AU - Zabludoff, Ann I

AU - Narayanan, Desika

AU - Shirley, Yancy L

AU - Walter, Fabian

AU - Smith, John David

AU - Tremonti, Christy A.

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KW - radio lines: galaxies

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