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Title: Enhancement of CO(3-2)/CO(1-0) ratios and star formation efficiencies in supergiant H II regions

We present evidence that super giant H II regions (GHRs) and other disk regions of the nearby spiral galaxy, M33, occupy distinct locations in the correlation between molecular gas, Σ{sub H{sub 2}}, and the star formation rate surface density, Σ{sub SFR}. This result is based on wide-field and high-sensitivity CO(3-2) observations at 100 pc resolution. Star formation efficiencies (SFEs), defined as Σ{sub SFR}/Σ{sub H{sub 2}}, in GHRs are found to be ∼1 dex higher than in other disk regions. The CO(3-2)/CO(1-0) integrated intensity ratio, R {sub 3-2/1-0}, is also higher than the average over the disk. Such high SFEs and R {sub 3-2/1-0} can reach the values found in starburst galaxies, which suggests that GHRs may be the elements building up a larger-scale starburst region. Three possible contributions to high SFEs in GHRs are investigated: (1) the I {sub CO}-N(H{sub 2}) conversion factor, (2) the dense gas fraction traced by R {sub 3-2/1-0}, and (3) the initial mass function (IMF). We conclude that these starburst-like properties in GHRs can be interpreted by a combination of both a top-heavy IMF and a high dense gas fraction, but not by changes in the I {sub CO}-N(H{sub 2}) conversion factor.
Authors:
; ; ; ; ; ;  [1] ;  [2] ;  [3] ; ;  [4] ;  [5] ;  [6] ; ;  [7] ;  [8]
  1. National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588 (Japan)
  2. Institute of Astronomy, School of Science, The University of Tokyo, Osawa, Mitaka, Tokyo 181-0015 (Japan)
  3. Joetsu University of Education, Yamayashiki-machi, Joetsu, Niigata 943-8512 (Japan)
  4. Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1805 (Japan)
  5. Department of Mathematical and Physical Sciences, Faculty of Science, Japan Woman's University, Mejirodai 2-8-1, Bunkyo, Tokyo 112-8681 (Japan)
  6. Department of Astronomical Science, The Graduate University for Advanced Studies (Sokendai), 2-21-1 Osawa, Mitaka, Tokyo 181-0015 (Japan)
  7. Osaka Prefecture University, Gakuen 1-1, Sakai, Osaka 599-8531 (Japan)
  8. Department of Physics, Meisei University, Hino, Tokyo 191-8506 (Japan)
Publication Date:
OSTI Identifier:
22356570
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 788; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CARBON MONOXIDE; CONVERSION; CORRELATIONS; DENSITY; EFFICIENCY; GALAXIES; HYDROGEN; MASS; RESOLUTION; SENSITIVITY; SPIRAL CONFIGURATION; STARS; SUPERGIANT STARS