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Title: THE CO-TO-H{sub 2} CONVERSION FACTOR AND DUST-TO-GAS RATIO ON KILOPARSEC SCALES IN NEARBY GALAXIES

We present ∼kiloparsec spatial resolution maps of the CO-to-H{sub 2} conversion factor (α{sub CO}) and dust-to-gas ratio (DGR) in 26 nearby, star-forming galaxies. We have simultaneously solved for α{sub CO} and the DGR by assuming that the DGR is approximately constant on kiloparsec scales. With this assumption, we can combine maps of dust mass surface density, CO-integrated intensity, and H I column density to solve for both α{sub CO} and the DGR with no assumptions about their value or dependence on metallicity or other parameters. Such a study has just become possible with the availability of high-resolution far-IR maps from the Herschel key program KINGFISH, {sup 12}CO J = (2-1) maps from the IRAM 30 m large program HERACLES, and H I 21 cm line maps from THINGS. We use a fixed ratio between the (2-1) and (1-0) lines to present our α{sub CO} results on the more typically used {sup 12}CO J = (1-0) scale and show using literature measurements that variations in the line ratio do not affect our results. In total, we derive 782 individual solutions for α{sub CO} and the DGR. On average, α{sub CO} = 3.1 M{sub ☉} pc{sup –2} (K km s{sup –1}){sup –1}more » for our sample with a standard deviation of 0.3 dex. Within galaxies, we observe a generally flat profile of α{sub CO} as a function of galactocentric radius. However, most galaxies exhibit a lower α{sub CO} value in the central kiloparsec—a factor of ∼2 below the galaxy mean, on average. In some cases, the central α{sub CO} value can be factors of 5-10 below the standard Milky Way (MW) value of α{sub CO,{sub MW}} = 4.4 M{sub ☉} pc{sup –2} (K km s{sup –1}){sup –1}. While for α{sub CO} we find only weak correlations with metallicity, the DGR is well-correlated with metallicity, with an approximately linear slope. Finally, we present several recommendations for choosing an appropriate α{sub CO} for studies of nearby galaxies.« less
Authors:
;  [1] ;  [2] ; ;  [3] ; ;  [4] ; ;  [5] ;  [6] ;  [7] ; ;  [8] ;  [9] ;  [10] ;  [11] ;  [12] ;  [13] ;  [14] ;  [15] more »; « less
  1. Max Planck Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
  2. National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
  3. Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
  4. Department of Physics and Astronomy, Mail Drop 111, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States)
  5. Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001 (United States)
  6. Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada)
  7. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
  8. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
  9. Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794-3800 (United States)
  10. Observatorio Astronómico Nacional, Alfonso XII, 3, E-28014 Madrid (Spain)
  11. Institut für theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg (Germany)
  12. Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom)
  13. ASTRON, The Netherlands Institute for Radio Astronomy, Postbus 2, 7990-AA Dwingeloo (Netherlands)
  14. Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States)
  15. Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States)
Publication Date:
OSTI Identifier:
22270622
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; APPROXIMATIONS; ASTRONOMY; ASTROPHYSICS; CARBON MONOXIDE; CORRELATIONS; COSMIC DUST; HYDROGEN; HYDROGEN 1; MILKY WAY; MOLECULES; SPATIAL RESOLUTION; STARS; VARIATIONS