Dust Extinction and SDSSV Milky Way Mapper

Discussion slides for SDSSV Milky Way Mapper telecon.

Transcript

1. Dust Extinction
   Karl D. Gordon
   Astronomer
   STScI, Baltimore, MD
   Milky Way Mapper Dust Telecon
   27 Feb 2023
   kgordon@stsci.edu
   @karllark@astrodon.social
   karllark@github
   

   View Slide

2. 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
   

   View Slide

3. 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
   

   View Slide

4. Witt, Bohlin, & Stecher 1984, 279, 698
   

   View Slide

5. 2175 A Bump
   width → strong variation
   center → almost no variation
   Fitzpatrick & Massa (1986, ApJ, 307, 286)
   

   View Slide

6. Fitzpatrick & Massa 1988, ApJ, 328, 734
   

   View Slide

7. Ultraviolet decomposed
   

   View Slide

8. Cardelli, Clayton, & Mathis 1988, ApJ, 329L, 33; 1989, ApJ, 345, 245
   

   View Slide

9. Valencic, Clayton, & Gordon 2004, ApJ, 616, 912
   

   View Slide

10. View Slide

11. 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
    

    View Slide

12. Marjorie Decleir
    

    View Slide

13. 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
    

    View Slide

14. View Slide

15. View Slide

16. Variations and 1st Direct Comparison of UV and MIR
    Strong variation
    Not correlated
    with grain size
    Silicates not correlated
    with 2175 A bump
    

    View Slide

17. Measuring A(V)
    w/ E(B-V) get R(V) = A(V)/E(B-V)
    Scatter ~ 7% Scatter ~ 3%
    I3 = 5.6 μm
    

    View Slide

18. In preparation
    Based on spectroscopy
    at all wavelengths
    

    View Slide

19. Average
    Variation with
    R(V)/grain size
    

    View Slide

20. Intriguing deviations
    

    View Slide

21. Coagulation?
    

    View Slide

22. Processing?
    

    View Slide

23. Thanks
    

    View Slide

24. Pair Method
    Github: karllark/measure_extinction
    OB stars ideal targets
    Luminous at all wavelengths
    Fairly simple atmospheres
    

    View Slide

25. 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.,
    

    View Slide

26. Slide from Dries Van De Puttte
    

    View Slide

27. MRN Bare Grains Model
    Mathis, Rumpl, & Nordsieck (1977, ApJ, 217, 425)
    

    View Slide

28. Updated Bare Grain Model
    Weingartner & Draine (2003)
    

    View Slide

29. Coated Grains
    Model
    Jones et al. (2013)
    

    View Slide

30. View Slide