How to Choose a Model

The dust_extinction package provides a suite of dust extinction models. Which model to use can depend on the wavelength range of interest, the expected type of extinction, or some other property.

Average Models

Simple Average Curves

These are straightforward averages of observed extinction curves. They are the simplest models and include models for the MW (RL85_MWGC, I05_MWAvg, CT06_MWLoc, CT06_MWGC, GCC09_MWAvg, F11_MWGC; Note the different valid wavelength ranges), the LMC (G03_LMCAvg, G03_LMC2) and the SMC (G03_SMCBar).

One often used alternative to these straight average models is to use one of the parameter dependent models with the average R(V) value. For the Milky Way, the usual average used is R(V) = 3.1.

Model x range [1/micron] wavelength range [micron] galaxy
GCC09_MWAvg 0.3 - 10.96 0.0912 - 3.3 MW
I05_MWAvg 0.13 - 0.8 1.24 - 7.76 MW
CT06_MWLoc 0.037 - 0.8 1.24 - 27.0 MW (Local)
RL85_MWGC 0.08 - 0.8 1.25 - 13.0 MW (GCenter)
CT06_MWGC 0.037 - 0.8 1.24 - 27.0 MW (GCenter)
F11_MWGC 0.05 - 0.8 1.28 - 19.1 MW (GCenter)
G03_LMCAvg 0.3 - 10.0 0.1 - 3.3 LMC
G03_LMC2 0.3 - 10.0 0.1 - 3.3 LMC (30 Dor)
G03_SMCBar 0.3 - 10.0 0.1 - 3.3 SMC

Parameter Dependent Average Curves

The models that are dependent on parameters provide average curves that account for overall changes in the extinction curve shapes. For example, the average behavior of Milky Way extinction curves has been shown to be dependent on R(V) = A(V)/E(B-V). R(V) roughly tracks with the average dust grain size.

The most general model is G16 as this model encompasses the average measured behavior of extinction curves in the MW, LMC, and SMC. The G16 model reduces to the F99 model with fA= 1.0. If only MW type extinction is expected, then the F19 model should be considered as it is based on spectroscopic extinction curves in the optical and ultraviolet and significantly more extinction curves than the CCM89 or O94 models.

Model Parameters x range [1/micron] wavelength range [micron] galaxy
CCM89 R(V) 0.3 - 10.0 0.1 - 3.3 MW
O94 R(V) 0.3 - 10.0 0.1 - 3.3 MW
F99, F04 R(V) 0.3 - 10.0 0.1 - 3.3 MW
VCG04 R(V) 3.3 - 8.0 0.125 - 0.31 MW
GCC09 R(V) 3.3 - 11.0 0.091 - 0.31 MW
M14 R_5495 0.3 - 3.3 0.31 - 3.3 MW, LMC
G16 R(V)_A, f_A 0.3 - 10.0 0.1 - 3.3 MW, LMC, SMC
F19 R(V) 0.3 - 8.7 0.115 - 3.3 MW

Notes

The GCC09 model is the only model that applies all the way to 912 A, but has the limitation that it only applies to the UV spectral region (not derived in the NIR/Optical).

The M14 models focus on refining models in the optical, and use the CCM89 models for the NIR and the UV. The M14 models use R_5495 = A(5485)/E(4405-5495), the spectroscopic equivalent to band-integrated R(V); see the paper for discussion. Because of a spurious feature in the near UV caused by smoothly tying their optical to the CCM89 UV, only the NIR and optical portions of the M14 models are provided here.

Shape Models

The models that focus on describing the full extinction curve shape are usually used to fit measured extinction curves. These models allow features in the extinction curve to be measured (e.g., 2175 A bump or 10 micron silicate feature). The P92 is the most general as it covers the a very broad wavelength range. The FM90 model has been extensively used, but only covers the UV wavelength range.

Model x range [1/micron] wavelength range [micron] # of parameters
FM90 3.13 - 11.0 0.0912 - 0.32 6
P92 0.001 - 1000 0.001 - 1000 19 (24 possible)