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J/ApJ/835/217    Density distributions for mm-wave line ratios    (Leroy+, 2017)

Millimeter-wave line ratios and sub-beam volume density distributions. Leroy A.K., Usero A., Schruba A., Bigiel F., Kruijssen J.M.D., Kepley A., Blanc G.A., Bolatto A.D., Cormier D., Gallagher M., Hughes A., Jimenez-Donaire M.J., Rosolowsky E., Schinnerer E. <Astrophys. J., 835, 217-217 (2017)> =2017ApJ...835..217L (SIMBAD/NED BibCode)
ADC_Keywords: Millimetric/submm sources ; Interstellar medium ; Models ; Radio lines Keywords: galaxies: ISM; galaxies: star formation; ISM: clouds; ISM: molecules; ISM: structure; radio lines: ISM Abstract: We explore the use of mm-wave emission line ratios to trace molecular gas density when observations integrate over a wide range of volume densities within a single telescope beam. For observations targeting external galaxies, this case is unavoidable. Using a framework similar to that of Krumholz & Thompson (2007ApJ...669..289K), we model emission for a set of common extragalactic lines from lognormal and power law density distributions. We consider the median density of gas that produces emission and the ability to predict density variations from observed line ratios. We emphasize line ratio variations because these do not require us to know the absolute abundance of our tracers. Patterns of line ratio variations have the potential to illuminate the high-end shape of the density distribution, and to capture changes in the dense gas fraction and median volume density. Our results with and without a high-density power law tail differ appreciably; we highlight better knowledge of the probability density function (PDF) shape as an important area. We also show the implications of sub-beam density distributions for isotopologue studies targeting dense gas tracers. Differential excitation often implies a significant correction to the naive case. We provide tabulated versions of many of our results, which can be used to interpret changes in mm-wave line ratios in terms of adjustments to the underlying density distributions. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table2.dat 22 1512 Density for maximum emissivity in one zone models table3.dat 70 105840 Beam averaged emissivity and density distributions
See also: J/A+A/432/369 : Leiden Atomic and Molecular Database (LAMDA) (Schoeier+, 2005) J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008) J/ApJS/175/509 : Ammonia spectral atlas in Perseus (Rosolowsky+, 2008) J/ApJ/723/1019 : Galactic SFR and gas surface densities (Heiderman+, 2010) J/A+A/581/A74 : Molecular clouds as viewed by ATLASGAL (Abreu-Vicente+, 2015) Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 6 A6 --- Line Emission line (G1) 8- 11 F4.1 K Tkin [10/50] Kinetic temperature 13- 17 F5.2 [-] logtau [-1/1] Optical depth, log 19- 22 F4.2 [cm-3] lognH2 [1.4/6] Log effective collider density for 95% peak emissivity
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 6 A6 --- Line Emission line (G1) 8- 21 A14 --- Shape Distribution shape ("LOGNORMAL" or "LOGNORMAL+TAIL") 23- 26 F4.2 [cm-3] logn0 [2/4] Mean Density 28- 30 F3.1 [-] sigma [0.6/1.2] Distribution width (1) 32- 36 F5.2 [-] logXmol [-8/-4] Adopted abundance relative to H2 38- 41 F4.2 [cm-3] logn-M [2/6] Median density by mass 43- 47 F5.2 --- logfden [-4/-0] Dense gas mass fraction (2) 49- 52 F4.1 K Tkin [15/35] Kinetic temperature 54- 58 F5.2 [-] logtau [-1/1] Adopted optical depth, log 60- 65 F6.2 logEmH2 [-23/-18] Beam averaged emissivity (( 67- 70 F4.2 [cm-3] lognem [2/6] Median density for emission
Note (1): Root mean square dispersion in lognormal part of density distribution. Note (2): Dense gas mass fraction, defined as gas above nH2=104.5cm-3
Global note: Note (G1): Lines are 12CO10, 12CO21, 12CO32, 13CO10, CS21, HCN10, HCOP10 or HNC10.
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Aug-2017
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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