Spectroscopic Extinction from FUV to MIR in Milky Way – Overall quite smooth – Few broad features including some new ones – Intriguing correlation, comforting non-correlations – One R(V) extinction relationship for all wavelengths • Beyond Milky Way – Mostly like the the Milky Way, but not all • Future w/ HST and JWST – More galaxies, more environments, larger samples
and shape • Clues in the continuum and features • Straightforward measurement • Focus on spectroscopic measurements • Biased by my views, not comprehensive
• Dust emission • Atomic composition of dust (e.g., depletions) • Dust Polarization • Dust grain models • All important, but not the focus of this talk
of line-of-sight – Specific to a point source dust – Proportional to dust grain properties • Attenuation – scattering into the line-of-sight – Varying extinction to stars – Applies to galaxies, circumstellar dust, etc.
as we are astronomers) Normalize so measurements with different dust columns can be compared A(V) determined by extrapolating to infinite wavelength e.g.,
extinction studies – Generally A(V) values less than a few – No 3.0 μm H2 0 ice feature • Dense sightlines – Generally studied in the NIR/MIR only – Have 3.0 μm H2 0 ice feature Decleir et al. (2022, ApJ, 930, 15) H20 Ice
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
FUV smooth & consistent with feature peaking ~800 Å – H2 correlates with FUV rise → co-spatial! – New optical features → unknown origin – NIR powerlaw & may contain H2 0 ice – MIR versus UV features → 2175 Å not due to silicates – R(V) dependent extinction relationship → on relationship for all wavelengths
curves are found in the star forming bar of the SMC! Ha image of the SMC Gordon & Clayton (1998, ApJ, 500, 816) Gordon et al. (2003, ApJ, 594, 279) STIS
MW • Radial, metallicity variations • 1st measurements in M33 Petia Yanchulov Merica-Jones Clayton, G et al., in prep Yanchulov M-J, P. et al., in prep
– Most of LMC similar to MW – Differences in LMC2 Supershell (near 30 Dor) • Small Magellanic Cloud (1/5 solar) – Most very different from MW (very steep, no bump) – Small fraction, closer to MW (flatter w/ bump) • M31 (~solar) and M33 (½ solar) – Similar to MW (preliminary)
Spectroscopic Extinction from FUV to MIR in Milky Way – Overall quite smooth, few broad features, DIBs (dust?) only narrow features – New broad features found in the optical – Intriguing correlations (or not) between features and gas tracers (esp. H2 ) – One R(V) extinction relationship for all wavelengths • Beyond Milky Way – Most of LMC, small fraction of SMC, M31, & M33 → similar to Milky Way – SMC & LMC2 Supershell region → weaker/non-existent bumps, stronger UV slope • Future w/ HST and JWST – More galaxies, more environments, larger samples