Dust Emission Spectra from Draine & Li (2007)
This directory contains results of theoretical modeling of infrared
emission from dust grains heated by starlight, as described in Draine
& Li (2007) -- please consult that paper for details.
In brief, the dust consists of a mixture of amorphous silicate grains
and carbonaceous grains. The carbonaceous grains have the properties
of PAH molecules and ions when the effective radius a < 5.0nm, the
properties of graphite spheres when a >> 10 nm, and optical properties
intermediate between the properties of PAH particles and graphite
particles for 5 < a < 10 nm, as described by Draine & Li (2007).
The ionization fraction x_ion(a) of the PAH particles is assumed to be
the average for the diffuse ISM [see Figure 8 of Draine & Li (2007)].
Temperature distribution functions are calculated for all particles
small enough for quantized heating to be important; large grains are
treated as having steady-state temperatures determined by starlight
heating = radiative cooling.
Spectra are given for dust heated by starlight with the spectrum of
Mathis, Mezger, & Panagia (1983), scaled by a factor U. U=1
corresponds to the starlight intensity estimate for the local ISM.
Band-averaged emissivities are also given for photometric bands used
by IRAS, COBE-DIRBE, Spitzer Space Telescope, Akari, and Herschel.
Spectra are given for 11 dust models:
jm name q_PAH
-- -------- ------
1 MW3.1_00 0.47 %
2 MW3.1_10 1.12 %
3 MW3.1_20 1.77 %
4 MW3.1_30 2.50 %
5 MW3.1_40 3.19 %
6 MW3.1_50 3.90 %
7 MW3.1_60 4.58 %
8 LMC2_00 0.75 %
9 LMC2_05 1.49 %
10 LMC2_10 2.37 %
11 smc 0.10 %
q_PAH is the fraction of the total dust mass that is contributed by
PAH particles containing < 1000 C atoms. All dust models use the dust
size distributions from Weingartner & Draine (2001), except for
adjustment of the parameters (a_01,a_02,sigma_1,sigma_2)
characterizing the PAH size distribution (see Draine & Li 2007, Table
2).
For each emission model, the dust is assumed to be exposed to a range
of radiation intensities, with the mass dM of dust exposed to
starlight intensities in [U,U+dU] being given by a power-law
distribution
dM = const * U^{-2} * dU for umin < U < umax
Results are available here for the following values of umin:
umin= 0.10, 0.15, 0.20, 0.30, 0.40, 0.50, 0.70, 0.80, 1.00, 1.20,
1.50, 2.00, 2.50, 3.00, 4.00, 5.00, 7.00, 8.00, 10.0, 12.0, 15.0,
20.0, 25.0
and for the following values of umax:
umax= 1e3, 1e4, 1e5, 1e6, 1e7
The model spectra are given in files
Uumin/Uumin_umax_modl.txt [e.g., U1.00/U1.00_1e6_MW3.1_60.txt ]
We also consider dust exposed to a single radiation intensity. This
is simply the case where umax = umin. These spectra are given in files
Uumin/Uumin_umin_modl.txt [e.g., U1.00/U1.00_1.00_MW3.1_60.txt ]
The files are ascii, and should be self-explanatory.
Draine & Li (2007) propose fitting emission from galaxies, or large
regions within a galaxy, by a linear sum of emission from dust heated
by a single radiation intensity U=umin plus emission from dust heated
by a distribution of starlight intensities ranging from umin to umax,
with umax=1e6 appearing to often work well for star-forming galaxies.
The emission spectrum, expressed as emission per H nucleon, is then
simply
j_nu = (1-gamma)*j_nu[umin,umin] + gamma*j_nu[umin,umax]
where gamma is the fraction of the total dust mass that is heated by
the distribution of starlight intensities [the remaining fraction
(1-gamma) is heated by starlight with U=umin], and j_nu[umin,umax] is
the emissivity from the file U$umin_umax_dustmod where dustmod is one
of {MW3.1_00, MW3.1_10, MW3.1_20, MW3.1_30, MW3.1_40, MW3.1_50,
MW3.1_60, LMC2_00, LMC2_05, LMC2_10, smc}.
Portions of the file U1.00/U1.00_1.00_MW3.1_60.txt are appended below.
References:
Draine, B.T., & Li, A. (2001), "Infrared Emission from Intersellar
Dust, I. Stochastic Heating of Small Grains", ApJ, 551, 807-824
Draine, B.T., & Li, A. (2007), "Infrared Emission from Interstellar
Dust, IV. The Silicate-Graphite-PAH Model in the Post-Spitzer Era",
ApJ, 657, 810-837
Li, A, & Draine, B.T. (2001), "Infrared Emission from Intersellar
Dust, II. The Diffuse Interstellar Medium", ApJ, 554, 778-802
Weingartner, J.C., & Draine, B.T. (2001), "Dust Grain Size
Distributions and Extinction in the Milky Way, LMC, and SMC", ApJ,
548, 296-309
Appendix: The File U1.00/U1.00_1.00_MW3.1_60.txt
=================================================
The first part of the file gives some model properties, including the
spectrum convolved with 23 photometric bands used by COBE-DIRBE, IRAS,
Spitzer Space Telescope, Akari, and Herschel
%%%%%%%%%%%%%%%%%%%%% first 53 lines follow %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Dust emission from Draine & Li (2007), ApJ 657, 810-837
==========================================================
7 = grain model
4.000E-08 4.000E-01 4.500E-05 = a_01 (cm) , sigma_1 , b_C1/0.92
2.000E-07 5.500E-01 1.500E-05 = a_02 (cm) , sigma_2 , b_C2/0.92
1.000E+00 1.000E+00 1.000E+00 = Umin , Umax, beta (dN/dU propto U^{-beta})
1.000E+00 = <U>
mmp83 = radfield
4.558E-24 = power/H (erg s-1)
band nu*P_nu(band) j_nu(band)
(um) (erg s-1 H-1)(Jy cm2 sr-1 H-1)
1.270E+00 1.841E-26 6.202E-19 COBE-DIRBE
2.220E+00 2.349E-26 1.383E-18 COBE-DIRBE
3.530E+00 1.526E-25 1.429E-17 COBE-DIRBE
4.880E+00 6.843E-26 8.858E-18 COBE-DIRBE
1.229E+01 5.872E-25 1.914E-16 COBE-DIRBE
2.079E+01 3.442E-25 1.898E-16 COBE-DIRBE
5.599E+01 7.648E-25 1.136E-15 COBE-DIRBE
9.770E+01 2.311E-24 5.988E-15 COBE-DIRBE
1.479E+02 2.610E-24 1.024E-14 COBE-DIRBE
2.479E+02 1.127E-24 7.407E-15 COBE-DIRBE
1.200E+01 6.488E-25 2.065E-16 IRAS
2.500E+01 3.008E-25 1.995E-16 IRAS
6.000E+01 9.037E-25 1.438E-15 IRAS
1.000E+02 2.380E-24 6.312E-15 IRAS
3.550E+00 1.775E-25 1.671E-17 SST-IRAC
4.493E+00 4.980E-26 5.935E-18 SST-IRAC
5.731E+00 3.961E-25 6.021E-17 SST-IRAC
7.872E+00 9.580E-25 2.000E-16 SST-IRAC
2.368E+01 2.646E-25 1.662E-16 SST-MIPS
7.142E+01 1.243E-24 2.355E-15 SST-MIPS
1.559E+02 2.443E-24 1.010E-14 SST-MIPS
1.600E+01 4.360E-25 1.850E-16 SST-IRSPU
2.200E+01 2.913E-25 1.700E-16 SST-IRSPU
7.500E+01 1.045E-24 2.078E-15 Herschel-PACS
1.100E+02 1.757E-24 5.127E-15 Herschel-PACS
1.700E+02 1.866E-24 8.416E-15 Herschel-PACS
2.500E+02 9.866E-25 6.542E-15 Herschel-SPIRE
3.600E+02 3.264E-25 3.116E-15 Herschel-SPIRE
5.200E+02 8.803E-26 1.214E-15 Herschel-SPIRE
2.400E+00 2.633E-26 1.676E-18 Akari IRC NIR N2
3.200E+00 1.174E-25 9.966E-18 Akari IRC NIR N3
4.100E+00 5.402E-26 5.875E-18 Akari IRC NIR N4
7.000E+00 1.088E-24 2.020E-16 Akari IRC MIR-S S7
9.000E+00 7.666E-25 1.830E-16 Akari IRC MIR-S S9W
1.100E+01 5.932E-25 1.731E-16 Akari IRC MIR-S S11
1.500E+01 4.522E-25 1.799E-16 Akari IRC MIR-L L15
1.800E+01 3.594E-25 1.716E-16 Akari IRC MIR-L L18W
2.400E+01 2.800E-25 1.782E-16 Akari IRC MIR-L L24
6.500E+01 1.127E-24 1.942E-15 Akari FIS N60
8.000E+01 1.945E-24 4.127E-15 Akari FIS WIDE-S
1.400E+02 2.632E-24 9.775E-15 Akari FIS WIDE-L
1.600E+02 2.431E-24 1.032E-14 Akari FIS N160
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
Below this are some blank lines, followed by the emission spectrum
between 1 cm and 1 micron (lines 62 - 1062, in frequency steps of
10**0.004). The quantities tabulated are nu* dP/d\nu (where \nu is
frequency, and P = power radiated per H nucleon) and j_\nu = power
radiated per H nucleon per unit frequency per steradian. Obviously,
j_\nu = (1/4*\pi)*(dP/d\nu)
%%%%%%%%%%%%%%%%%%%%%%%%%%% lines 60 - 70 follow %%%%%%%%%%%%%%%%%%%%%%
lambda nu*dP/dnu j_nu
(um) (erg s-1 H-1)(Jy cm2 sr-1 H-1)
1.000E+04 5.303E-31 1.407E-19
9.908E+03 5.497E-31 1.445E-19
9.817E+03 5.697E-31 1.484E-19
9.727E+03 5.905E-31 1.524E-19
9.638E+03 6.120E-31 1.565E-19
9.550E+03 6.344E-31 1.607E-19
9.462E+03 6.575E-31 1.650E-19
9.376E+03 6.815E-31 1.695E-19
9.290E+03 7.063E-31 1.741E-19
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%