Dust Extinction Karl D. Gordon Astronomer STScI, Baltimore, MD Milky Way Mapper Dust Telecon 27 Feb 2023 [email protected] @[email protected] karllark@github
Some Thoughts ● Detailed knowledge of extinction – Biased to low A(V) – Biased to withing 1 kpc of Sun + LMC/SMC ● 3D mapping of A(V) & R(V) – Probe specific physical environments – Hints from MW and LMC/SMC – R(V) dependent average relationship not the full story – Significant variations in UV and NIR/MIR
Wavelength axis variations Allow full FUV-MIR extinction to be seen Wavelength scale is proportional to energy Emphasizes UV wavelengths Versus λ Versus 1/λ UV Opt NIR MIR
Broad Optical Features (origin unknown) Long known Very Broad Structure Explained! Massa, Fitzpatrick, Gordon, et al. 2020, ApJ, 891, 67 Centers: 4370, 4870, & 6300 Å Widths: ~10% Two blue correlate w/ 2175 Å
3.0 μm ice feature measured in the diffuse average at A(ice)/A(V) = 0.0019 +/- 0.007 Not a significant detection, but intriguing at the level predicted by Potapov et al. (2021) if ice is present in shadowed pits in silicate grains
Basic measurement is the color “excess” versus wavelength (in magnitudes as we are astronomers) Normalize so measurements with different dust columns can be compared A(V) determined by extrapolating to infinite wavelength e.g.,