title: Highly efficient star formation in NGC 5253 possibly from stream-fed accretion.
abstract: Gas clouds in present-day galaxies are inefficient at forming stars. Low star-formation efficiency is a critical parameter in galaxy evolution: it is why stars are still forming nearly 14 billion years after the Big Bang and why star clusters generally do not survive their births, instead dispersing to form galactic disks or bulges. Yet the existence of ancient massive bound star clusters (globular clusters) in the Milky Way suggests that efficiencies were higher when they formed ten billion years ago. A local dwarf galaxy, NGC 5253, has a young star cluster that provides an example of highly efficient star formation. Here we report the detection of the J = 3→2 rotational transition of CO at the location of the massive cluster. The gas cloud is hot, dense, quiescent and extremely dusty. Its gas-to-dust ratio is lower than the Galactic value, which we attribute to dust enrichment by the embedded star cluster. Its star-formation efficiency exceeds 50 per cent, tenfold that of clouds in the Milky Way. We suggest that high efficiency results from the force-feeding of star formation by a streamer of gas falling into the galaxy.
authors: Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095-1547, USA.
authors: J L
authors: JL
authors: Turner
authors: Department of Physics and Astronomy, University of Tel Aviv, 69978 Ramat Aviv, Israel.
authors: S C
authors: SC
authors: Beck
authors: Observational Cosmology Laboratory, Code 665, NASA at Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
authors: D J
authors: DJ
authors: Benford
authors: Department of Physics and Astronomy, University of California, Los Angeles, Los Angeles, California 90095-1547, USA.
authors: S M
authors: SM
authors: Consiglio
authors: Academia Sinica, Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, AS/NTU No. 1, Sec. 4, Roosevelt Road, Taipei 10617, Taiwan.
authors: P T P
authors: PT
authors: Ho
authors: Department of Physics, Caltech, Pasadena, California 91125, USA; Institute for Astrophysics, University of Minnesota, Minneapolis, Minnesota 55405, USA.
authors: A
authors: A
authors: Kovács
authors: 1] Department of Physics, New Mexico Institute of Mining and Technology, Socorro, New Mexico 85723, USA [2] National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, New Mexico 85723, USA.
authors: D S
authors: DS
authors: Meier
authors: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, USA.
authors: J-H
authors: JH
authors: Zhao