Slide 1

Slide 1 text

Dust Extinction in the Diffuse Interstellar Medium Karl D. Gordon, Astronomer STScI, Baltimore, MD, USA Cardiff University School of Physics & Astronomy 19 Apr 2023 [email protected] @astrodon.social karllark@github “Have Dust – Will Study” Slides on speakerdeck

Slide 2

Slide 2 text

Summary ● Extinction measurements are fundamental to understanding dust ● Spectroscopic Extinction from FUV to MIR in Milky Way – Overall quite smooth – Few broad features including some new ones – One intriguing correlation, comforting non-correlations – One R(V) extinction relationship for all wavelengths ● Beyond Milky Way (if there is time) – Mostly like the the Milky Way, but not all ● Future w/ HST and JWST – More galaxies, more environments, larger samples

Slide 3

Slide 3 text

Extinction ● Critical clues to dust grain abundance, size, composition, and shape ● Clues in the continuum and features ● Straightforward measurement ● Focus on spectroscopic measurements ● Biased by my views, not comprehensive

Slide 4

Slide 4 text

Not Covered ● Dust scattering (e.g., albedo, scattering phase function) ● Dust emission ● Atomic composition of dust (e.g., depletions) ● Dust Polarization ● Dust grain models ● All important, but not the focus of this talk

Slide 5

Slide 5 text

Extinction (not Attenuation) ● Extinction – Absorption and scattering out 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.

Slide 6

Slide 6 text

Extinction vs Attenuation Github: karllark/dust_attenuation Github: karllark/dust_extinction

Slide 7

Slide 7 text

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

Slide 8

Slide 8 text

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.,

Slide 9

Slide 9 text

Slide from Dries Van De Puttte

Slide 10

Slide 10 text

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

Slide 11

Slide 11 text

Diffuse vs Dense Dust ● Diffuse sightlines – Most detailed 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

Slide 12

Slide 12 text

Our Galaxy

Slide 13

Slide 13 text

Stecher 1969, ApJ, 157, 125

Slide 14

Slide 14 text

International Ultraviolet Explorer 18 years! 100,000 UV spectra!

Slide 15

Slide 15 text

No content

Slide 16

Slide 16 text

Witt, Bohlin, & Stecher 1984, 279, 698

Slide 17

Slide 17 text

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

Slide 18

Slide 18 text

Fitzpatrick & Massa 1988, ApJ, 328, 734

Slide 19

Slide 19 text

No content

Slide 20

Slide 20 text

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

Slide 21

Slide 21 text

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

Slide 22

Slide 22 text

Far Ultraviolet Spectroscopic Explorer 905 to 1195 Å

Slide 23

Slide 23 text

Pre-FUSE ORFEUS: Sasseen et al. 2002, ApJ, 566, 267 Voyager: Snow et al. 1990, ApJ, 399, L23 See also: Buss et al. 1994, France et al. 2004; Lewis et al. 2005

Slide 24

Slide 24 text

Gordon, Cartledge, & Clayton 2009, ApJ, 705, 1320 See also: Sofia et al. 2005

Slide 25

Slide 25 text

FUV (& all UV) extinction smooth Residuals due to stellar or ISM HI FUV rise consistent with feature peaking at ~800 Å

Slide 26

Slide 26 text

ApJ, 944, 33 Dries Van De Putte

Slide 27

Slide 27 text

FUV rise extinction component & H2 column Very strong correlation & goes through zero!!! Grain responsible for FUV rise and H2 co-spatial Not the case for the 2175 Å bump

Slide 28

Slide 28 text

Hubble Space Telescope 912 Å to 2.5 μm

Slide 29

Slide 29 text

Pre-Hubble ● Continuum measured mainly via photometry (until 2019) ● Except for Orion dust – Cadelli & Clayton (1988, AJ, 95, 516) ● Very Broad Structure with low resolution spectra – Next slide

Slide 30

Slide 30 text

Very Broad Structure = Deviations from linear w/ 1/lambda Whiteoak 1966, ApJ, 144, 305 Hayes 1973, IAUS, 53, 83

Slide 31

Slide 31 text

No content

Slide 32

Slide 32 text

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

Slide 33

Slide 33 text

NIR/MIR Extinction ● Continuum measured via photometry (until 2021) ● Features measured spectroscopically – Narrow wavelength ranges or towards “complicated” stars – 3.0 μm ice – 3.4 μm hydrocarbon – 10/20 μm silicate features

Slide 34

Slide 34 text

● Many ice features ● 3.0 μm H2 0 the strongest ● Requires A(V) > 3 Boogert, Gerakines, & Whittet

Slide 35

Slide 35 text

3.4 μm Hydrocarbon grains Pendelton & Allamandola (2002, ApJS, 138, 75)

Slide 36

Slide 36 text

10 & 20 μm Silicate Features Chiar & Tielens (2006, ApJ, 637, 774)

Slide 37

Slide 37 text

Crystalline Silicate Fraction ~0.2% (or zero) Kemper, Viernd, & Tielens (2004, ApJ, 609, 826) Amorphous Crystalline

Slide 38

Slide 38 text

NASA’s Infrared Telescope Facility 0.8 to 20 μm

Slide 39

Slide 39 text

Marjorie Decleir

Slide 40

Slide 40 text

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

Slide 41

Slide 41 text

Spitzer Space Telescope 3 to 160 μm

Slide 42

Slide 42 text

No content

Slide 43

Slide 43 text

No content

Slide 44

Slide 44 text

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

Slide 45

Slide 45 text

Putting all the Wavelengths Together

Slide 46

Slide 46 text

ApJ, in press Based on spectroscopy at all wavelengths

Slide 47

Slide 47 text

Fitting a Line New penultimate technique* ● Fully accounts for correlated x & y uncertainties ● Allows for different correlations for different points ● Line integral for each point *The authors await knowledge of what paper to cite where this was first shown (likely from decades ago)

Slide 48

Slide 48 text

Average Variation with R(V)/grain size

Slide 49

Slide 49 text

Significant Deviations from Literature Curves at Select R(V)

Slide 50

Slide 50 text

MW Extinction Summary ● Spectroscopic from FUV to MIR – 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 → one relationship for all wavelengths

Slide 51

Slide 51 text

Beyond Milky Way

Slide 52

Slide 52 text

Clayton & Martin 1985, ApJ, 288, 558 Add figure showing 30 Dor/LMC2

Slide 53

Slide 53 text

Misselt et al. (1999, ApJ, 515, 128)

Slide 54

Slide 54 text

Spatial Distribution Misselt et al. (1999, ApJ, 515, 128)

Slide 55

Slide 55 text

Prevot et al. 1984, A&A, 132, 389

Slide 56

Slide 56 text

SMC Extinction Curves Milky Way-like! (2175 Å bump) 4 similar 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

Slide 57

Slide 57 text

SMC AzV 456 SMC Bar LMC2 LMC General MW Quiescent Processed Continuum of Properties Gordon et al. (2003, ApJ, 594, 279) Gordon et al. (2016, ApJ, 826, 104)

Slide 58

Slide 58 text

No content

Slide 59

Slide 59 text

Using MW HI 21cm

Slide 60

Slide 60 text

Spatial Distribution 2175 A bump Yes / No Image: MIPS 24um

Slide 61

Slide 61 text

Clayton et al. 2015, ApJ, 815, 14

Slide 62

Slide 62 text

M31/M33 Extinction ● All w/ HST photometry ● Similar to 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

Slide 63

Slide 63 text

Beyond the MW Summary ● Large Magellanic Cloud (½ solar) – 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)

Slide 64

Slide 64 text

Future

Slide 65

Slide 65 text

HST ● More galaxies – Investigate low metallicity galaxies ● SMC unique? – Expand samples in large galaxies ● Milky Way R(V) dependent extinction relationship works? ● High/low R(V) – Probe extremes of dust size, curvature in R(V) relationship?

Slide 66

Slide 66 text

JWST ● Two cycle 1 programs (PIs: Decleir & Zeegers) – 21 Milky Way sightlines from 2.4-28 μm – Continuum and 3.4, 10, & 20 μm features ● Map features photometrically ● LMC/SMC continuum & silicate measurements ● Other galaxies (sensitivity?)

Slide 67

Slide 67 text

Photometric Feature Measurements 10 μm silicate 3 μm ice 3.4 μm hydrocarbon Burcu Günay

Slide 68

Slide 68 text

Summary ● Extinction measurements are fundamental to understanding dust ● 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

Slide 69

Slide 69 text

Thanks