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Journal Articles The Astrophysical Journal Year : 2022

Low-J CO Line Ratios from Single-dish CO Mapping Surveys and PHANGS-ALMA

Adam K. Leroy
  • Function : Author
Erik Rosolowsky
Antonio Usero
Karin Sandstrom
Eva Schinnerer
Andreas Schruba
  • Function : Author
Alberto D. Bolatto
  • Function : Author
Jiayi Sun
Ashley. T. Barnes
  • Function : Author
Francesco Belfiore
Frank Bigiel
Jakob S. den Brok
  • Function : Author
Yixian Cao
I. -Da Chiang
  • Function : Author
Mélanie Chevance
Daniel A. Dale
  • Function : Author
Cosima Eibensteiner
Christopher M. Faesi
  • Function : Author
Simon C. O. Glover
  • Function : Author
María J. Jiménez Donaire
  • Function : Author
Ralf S. Klessen
  • Function : Author
Eric W. Koch
  • Function : Author
J. M. Diederik Kruijssen
  • Function : Author
Daizhong Liu
Sharon E. Meidt
  • Function : Author
Hsi-An Pan
Jérôme Pety
Johannes Puschnig
Miguel Querejeta
Toshiki Saito
Amy Sardone
Elizabeth J. Watkins
  • Function : Author
Axel Weiss
Thomas G. Williams
  • Function : Author


We measure the low-J CO line ratios R 21 ≡ CO (2-1)/CO (1-0), R 32 ≡ CO (3-2)/CO (2-1), and R 31 ≡CO (3-2)/CO (1-0) using whole-disk CO maps of nearby galaxies. We draw CO (2-1) from PHANGS-ALMA, HERACLES, and follow-up IRAM surveys; CO (1-0) from COMING and the Nobeyama CO Atlas of Nearby Spiral Galaxies; and CO (3-2) from the James Clerk Maxwell Telescope Nearby Galaxy Legacy Survey and Atacama Pathfinder Experiment Large APEX Sub-Millimetre Array mapping. All together, this yields 76, 47, and 29 maps of R 21, R 32, and R 31 at 20″ ~ 1.3 kpc resolution, covering 43, 34, and 20 galaxies. Disk galaxies with high stellar mass, $\mathrm{log}({M}_{\star }/{M}_{\odot })=10.25\mbox{--}11$ , and star formation rate (SFR) = 1-5 M yr-1, dominate the sample. We find galaxy-integrated mean values and a 16%-84% range of R 21 = 0.65 (0.50-0.83), R 32 = 0.50 (0.23-0.59), and R 31 = 0.31 (0.20-0.42). We identify weak trends relating galaxy-integrated line ratios to properties expected to correlate with excitation, including SFR/M and SFR/L CO. Within galaxies, we measure central enhancements with respect to the galaxy-averaged value of ~ ${0.18}_{-0.14}^{+0.09}$ dex for R 21, ${0.27}_{-0.15}^{+0.13}$ dex for R 31, and ${0.08}_{-0.09}^{+0.11}$ dex for R 32. All three line ratios anticorrelate with galactocentric radius and positively correlate with the local SFR surface density and specific SFR, and we provide approximate fits to these relations. The observed ratios can be reasonably reproduced by models with low temperature, moderate opacity, and moderate densities, in good agreement with expectations for the cold interstellar medium. Because the line ratios are expected to anticorrelate with the CO (1-0)-to-H2 conversion factor, ${\alpha }_{\mathrm{CO}}^{1-0}$ , these results have general implications for the interpretation of CO emission from galaxies.
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Dates and versions

insu-03667457 , version 1 (14-05-2022)





Adam K. Leroy, Erik Rosolowsky, Antonio Usero, Karin Sandstrom, Eva Schinnerer, et al.. Low-J CO Line Ratios from Single-dish CO Mapping Surveys and PHANGS-ALMA. The Astrophysical Journal, 2022, 927, ⟨10.3847/1538-4357/ac3490⟩. ⟨insu-03667457⟩
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