AuthorFrench, K. Decker
Zabludoff, Ann I.
Smith, J. D.
AffiliationUniv Arizona, Steward Observ
MetadataShow full item record
PublisherIOP PUBLISHING LTD
CitationK. Decker French et al 2018 ApJ 861 123
Rights© 2018. The American Astronomical Society. All rights reserved.
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AbstractPost-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 earlytype galaxies. The HCN/CO luminosity ratio upper limits are low compared to star-forming and even many earlytype 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.
VersionFinal published version
SponsorsHubble Fellowship Grant [HST-HF2-51391.001-A]; Space Telescope Science Institute; NASA [NAS5-26555, ADP-NNX10AE88G]; NSF [AST-1724864, AST-1715206]; HST [AR-13906, 15043]; National Science Foundation Graduate Research Fellowship Program [DGE 1256260]; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science; Participating Institutions