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          Institute: MPI für Astronomie     Collection: Publikationen_mpia     Display Documents

ID: 730384.0, MPI für Astronomie / Publikationen_mpia
Variations in the star formation efficiency of the dense molecular gas across the disks of star-forming galaxies
Authors:Usero, A.; Leroy, A. K.; Walter, F.; Schruba, A.; García-Burillo, S.; Sandstrom, K.; Bigiel, F.; Brinks, E.; Kramer, C.; Rosolowsky, E.; Schuster, K.-F.; de Blok, W. J. G.
Date of Publication (YYYY-MM-DD):2015
Title of Journal:The Astronomical Journal
Issue / Number:4
Start Page:id. 115 (40) pp
Audience:Not Specified
Abstract / Description:We present a new survey of HCN(1–0) emission, a tracer of dense molecular gas, focused on the little-explored regime of normal star-forming galaxy disks. Combining HCN, CO, and infrared (IR) emission, we investigate the role of dense gas in star formation, finding systematic variations in both the apparent dense gas fraction (traced by the HCN-to-CO ratio) and the apparent star formation efficiency of dense gas (traced by the IR-to-HCN ratio). The latter may be unexpected, given the recent popularity of gas density threshold models to explain star formation scaling relations. Our survey used the IRAM 30 m telescope to observe HCN(1–0), CO(1–0), and several other emission lines across 29 nearby disk galaxies whose CO(2–1) emission has previously been mapped by the HERACLES survey. We detected HCN in 48 out of 62 observed positions. Because our observations achieve a typical resolution of ∼1.5 kpc and span a range of galaxies and galactocentric radii (56% lie at {r}{gal}\gt 1 kpc), we are able to investigate the properties of the dense gas as a function of local conditions in a galaxy disk. We focus on how the ratios IR-to-CO, HCN-to-CO, and IR-to-HCN (observational cognates of the star formation efficiency, dense gas fraction, and dense gas star formation efficiency) depend on the stellar surface density, {{{Σ }}}{star}, and the molecular-to-atomic gas ratio, {{{Σ }}}{mol}/{{{Σ }}}{atom}. The HCN-to-CO ratio is low, often ∼1/30, and correlates tightly with both the molecular-to-atomic ratio and the stellar mass surface density across a range of 2.1 dex (factor of ≈125) in both parameters. Thus for the assumption of fixed
Free Keywords:galaxies: ISM; galaxies: star formation; ISM: molecules; ISM: structure; radio lines: galaxies; radio lines: ISM
External Publication Status:published
Document Type:Article
Communicated by:N. N.
Affiliations:MPI für Astronomie
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