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Title: OPACITY BROADENING OF {sup 13}CO LINEWIDTHS AND ITS EFFECT ON THE VARIANCE-SONIC MACH NUMBER RELATION

We study how the estimation of the sonic Mach number (M{sub s} ) from {sup 13}CO linewidths relates to the actual three-dimensional sonic Mach number. For this purpose we analyze MHD simulations that include post-processing to take radiative transfer effects into account. As expected, we find very good agreement between the linewidth estimated sonic Mach number and the actual sonic Mach number of the simulations for optically thin tracers. However, we find that opacity broadening causes M{sub s} to be overestimated by a factor of ≈1.16-1.3 when calculated from optically thick {sup 13}CO lines. We also find that there is a dependence on the magnetic field: super-Alfvénic turbulence shows increased line broadening compared with sub-Alfvénic turbulence for all values of optical depth for supersonic turbulence. Our results have implications for the observationally derived sonic Mach number-density standard deviation (σ{sub ρ/(ρ)}) relationship, σ{sub ρ/〈ρ〉}{sup 2}=b{sup 2}M{sub s}{sup 2}, and the related column density standard deviation (σ {sub N/(N)}) sonic Mach number relationship. In particular, we find that the parameter b, as an indicator of solenoidal versus compressive driving, will be underestimated as a result of opacity broadening. We compare the σ {sub N/(N)}-M{sub s} relation derived from synthetic dust extinction mapsmore » and {sup 13}CO linewidths with recent observational studies and find that solenoidally driven MHD turbulence simulations have values of σ {sub N/(N)}which are lower than real molecular clouds. This may be due to the influence of self-gravity which should be included in simulations of molecular cloud dynamics.« less
Authors:
;  [1] ; ;  [2] ; ;  [3] ;  [4] ;  [5]
  1. Departamento de Física Teórica e Experimental, Universidade Federal do Rio Grande do Norte, 59072-970 (Brazil)
  2. Astronomy Department, University of Wisconsin, Madison, 475 North Charter Street, WI 53711 (United States)
  3. Physikalisches Institut der Universität zu Köln, Zülpicher Strasse 77, D-50937 Köln (Germany)
  4. Max-Planck-Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg (Germany)
  5. Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, 05508-090 (Brazil)
Publication Date:
OSTI Identifier:
22365926
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 785; 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; ALFVEN WAVES; CARBON 13; CARBON MONOXIDE; COMPARATIVE EVALUATIONS; COMPUTERIZED SIMULATION; COSMIC DUST; DENSITY; GRAVITATION; LINE BROADENING; LINE WIDTHS; MACH NUMBER; MAGNETIC FIELDS; MAGNETOHYDRODYNAMICS; OPACITY; RADIANT HEAT TRANSFER; THREE-DIMENSIONAL CALCULATIONS; TURBULENCE