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Milky Way dust extinction in the NIR

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.

Marjorie Decleir

October 26, 2020
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  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. 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
  3. pair method / = 5 reddened star comparison star of

    same spectral type dust extinction
  4. § 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
  5. 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 − = −
  6. 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
  7. 11 () () = ( − ) () + 1

    wavelength (µm) wavelength (µm) E(λ-V) () A(λ)/A(V) + offset
  8. 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
  9. 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)
  10. 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)
  11. 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 [email protected] 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