Milky Way dust extinction in the NIR

I gave this talk at the virtual conference "The Rise of Metals and Dust in Galaxies through Cosmic Time" in October 2020 (https://metals-dust.sciencesconf.org). It is about my ongoing project studying NIR dust extinction curves in the Milky Way, based on SpeX spectra.

Transcript

1. Milky Way Dust Extinction in the Near-Infrared Marjorie Decleir The Rise of Metals and Dust in Galaxies through Cosmic Time October 26, 2020
2. absorption 2 extinction attenuation geometry effects! scattering
3. absorption extinction wavelength (µm) 2175Å bump 3 scattering carbonaceous grains
4. 4 Pendleton & Allamandola (2002) 3.4 µm: HAC 3.05 µm: ice (hydrogenated amorphous carbon) Gordon+2000 1.5 µm: FeSi2 Gibb+2000 wavelength (µm) extinction wavelength (µm) extinction wavelength (µm) emission
5. pair method / = 5 reddened star comparison star of same spectral type dust extinction
6. § Medium-resolution spectrograph (R~2000) § NASA Infrared Telescope Facility (Mauna Kea) § 0.8 ‒ 5.5 µm IUE flux 2M ASS JHK SpeX LXD STIS IRS wavelength (µm) SpeX SXD 6
7. 7 wavelength (µm) wavelength (µm) flux
8. 8 wavelength (µm) flux
9. 9 − = reddening = differential extinction compared to V-band Need to be normalized to total dust extinction to compare with each other e.g. total extinction in V-band = A(V) What is A(V)? E(λ-V) wavelength (µm) E − = −
10. 10 E − = − = !" − Fitting a powerlaw model to the NIR extinction curve gives us a direct measurement for A(V)! ∞ − = − = − ( − ) = differential extinction (to V-band) () = total extinction at λ () = total extinction in V-band b = amplitude ⍺ = powerlaw index c = offset (e.g. Martin&Whittet 1990) = () ⟶ ∞ () ⟶ 0
11. 11 () () = ( − ) () + 1 wavelength (µm) wavelength (µm) E(λ-V) () A(λ)/A(V) + offset
12. 12 HAC? ice ?? wavelength (µm) A(λ)/A(V) HD283809 = 5.6 Whittet et al. (1988): ice if > 3.3 How low can we go? residual
13. 13 = () ( − ) = total-to-selective extinction grain size distribution smaller R(V) à more small grains larger R(V) à more large grains MW average: = 3.1 average ice? A(λ)/A(V) residual Cardelli+1989 = 3.16 wavelength (µm)
14. 14 ice? A(λ)/A(V) residual Cardelli+1989 = 3.16 Fit the features Better fit for continuum: How good is powerlaw? How does NIR extinction relate to UV/optical/MIR extinction? wavelength (µm)
15. 15 SpeX spectra bridge the gap Reddened / comparison = extinction NIR extinction = powerlaw ice Ice in A(V)=5.6 sightline Average R(V)=3.16 Questions? Contact me on Slack or mdecleir@stsci.edu wavelength (µm) wavelength (µm) wavelength (µm) wavelength (µm) wavelength (µm) wavelength (µm) A(λ)/A(V) residual A(λ)/A(V) residual E(λ-V) flux flux flux = 3.16