THE CO-TO-H{sub 2} CONVERSION FACTOR AND DUST-TO-GAS RATIO ON KILOPARSEC SCALES IN NEARBY GALAXIES
- Max Planck Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg (Germany)
- National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903 (United States)
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Department of Physics and Astronomy, Mail Drop 111, University of Toledo, 2801 West Bancroft Street, Toledo, OH 43606 (United States)
- Princeton University Observatory, Peyton Hall, Princeton, NJ 08544-1001 (United States)
- Department of Physics and Astronomy, McMaster University, Hamilton, Ontario L8S 4M1 (Canada)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA (United Kingdom)
- Department of Physics and Astronomy, SUNY Stony Brook, Stony Brook, NY 11794-3800 (United States)
- Observatorio Astronómico Nacional, Alfonso XII, 3, E-28014 Madrid (Spain)
- Institut für theoretische Astrophysik, Zentrum für Astronomie der Universität Heidelberg, Albert-Ueberle Str. 2, D-69120 Heidelberg (Germany)
- Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB (United Kingdom)
- Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States)
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} 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.
- OSTI ID:
- 22270622
- Journal Information:
- Astrophysical Journal, Vol. 777, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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