The empire survey: systematic variations in the dense gas fraction and star formation efficiency from full-disk mapping of M51

Journal Article · Tue May 10 04:00:00 EDT 2016 · Astrophysical Journal Letters

DOI:https://doi.org/10.3847/2041-8205/822/2/L26· OSTI ID:22869085

Bigiel, Frank; Jiménez-Donaire, Maria J.; Cormier, Diane ^[1]; Leroy, Adam K. ^[2]; Pety, Jérôme ^[3]; Usero, Antonio; Garcia-Burillo, Santiago ^[4]; Bolatto, Alberto ^[5]; Colombo, Dario ^[6]; González-García, Manuel ^[7]; Hughes, Annie ^[8]; Kepley, Amanda A. ^[9]; Kramer, Carsten ^[10]; Sandstrom, Karin ^[11]; others, and

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1. Institut für theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg (Germany)
2. Department of Astronomy, The Ohio State University, 140 W 18th Street, Columbus, OH 43210 (United States)
3. Institut de Radioastronomie Millimétrique (IRAM), 300 Rue de la Piscine, F-38406 Saint Martin d’Hères (France)
4. Observatorio Astronómico Nacional, Alfonso XII 3, E-28014 Madrid (Spain)
5. Department of Astronomy and Laboratory for Millimeter-Wave Astronomy, University of Maryland, College Park, MD 20742 (United States)
6. Department of Physics, University of Alberta, 4-181 CCIS, Edmonton, AB T6G 2E1 (Canada)
7. Instituto de Astrofísica de Andalucía IAA-CSIC, Glorieta de la Astronomía s/n, E-18008, Granada (Spain)
8. CNRS, IRAP, 9 Av. colonel Roche, BP 44346, F-31028 Toulouse cedex 4 (France)
9. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903-2475 (United States)
10. Instituto de Radioastronoma Milimtrica (IRAM), Av. Divina Pastora 7, Nucleo Central, E-18012 Granada (Spain)
11. Center for Astrophysics and Space Sciences, Department of Physics, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093 (United States)

We present the first results from the EMPIRE survey, an IRAM large program that is mapping tracers of high-density molecular gas across the disks of nine nearby star-forming galaxies. Here, we present new maps of the 3 mm transitions of HCN, HCO{sup +}, and HNC across the whole disk of our pilot target, M51. As expected, dense gas correlates with tracers of recent star formation, filling the “luminosity gap” between Galactic cores and whole galaxies. In detail, we show that both the fraction of gas that is dense, f{sub dense} traced by HCN/CO, and the rate at which dense gas forms stars, SFE{sub dense} traced by IR/HCN, depend on environment in the galaxy. The sense of the dependence is that high-surface-density, high molecular gas fraction regions of the galaxy show high dense gas fractions and low dense gas star formation efficiencies. This agrees with recent results for individual pointings by Usero et al. but using unbiased whole-galaxy maps. It also agrees qualitatively with the behavior observed contrasting our own Solar Neighborhood with the central regions of the Milky Way. The sense of the trends can be explained if the dense gas fraction tracks interstellar pressure but star formation occurs only in regions of high density contrast.

• OSTI ID: 22869085
• Journal Information: Astrophysical Journal Letters, Journal Name: Astrophysical Journal Letters Journal Issue: 2 Vol. 822; ISSN 2041-8205
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON MONOXIDE
COSMIC GASES
DENSITY
HYDROCYANIC ACID
LUMINOSITY
MAPPING
MILKY WAY
MOLECULAR IONS
STARS
SURFACES