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 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 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:
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FileName Lrecl Records Explanations
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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
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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
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Bytes Format Units Label Explanations
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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
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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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 K.km/s/cm-2 logEmH2 [-23/-18] Beam averaged emissivity
((K.km.s-1)/cm-2)
67- 70 F4.2 [cm-3] lognem [2/6] Median density for emission
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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
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Global note:
Note (G1): Lines are 12CO10, 12CO21, 12CO32, 13CO10, CS21, HCN10, HCOP10 or
HNC10.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Aug-2017