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Dust Extinction - Overview

This overview discusses the measurement and variation of dust extinction in local and high-redshift galaxies, focusing on methods such as local extinction curves, GRBs, lenses, SNe, galaxies, and QSOs.

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Dust Extinction - Overview

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  1. Dust Extinction - Overview Árdís Elíasdóttir Department of Astrophysical Sciences Princeton University (ardis@astro.princeton.edu) Current Problems in Extragalactic Dust NBI, Copenhagen Denmark 01.07.2009 www.astro.princeton.edu

  2. Outline • Local extinction curves • High-z extinction curves • GRBs • Lenses • SNe • Galaxies • QSOs www.astro.princeton.edu

  3. LOCAL EXTINCTION CURVES www.astro.princeton.edu

  4. Dusty Worlds • Dust between the stars in galaxies causes the dimming of light from background sources • Extinction curves measure this dimming as a function of wavelength • Traditionally measured by comparing two stars of the same spectral type • Important for • Galaxy formation studies • Dark energy surveys • Well determined for the Milky Way • Very little known about extragalactic dust extinction www.astro.princeton.edu

  5. Empirically determined Mean value is RV = 3.1 (blue) Extreme values: RV = 1.8 (green) and RV = 5.6-5.8 (red) (Cardelli et al. 1989, Fitzpatrick et al. 1999,Udalski 2003) Larger RV -> larger dust grains Bump at 2175 Å (4.6 m-1) Unknown origin Graphite? PAHs? The Galactic Extinction Curve “Reddening” (Cardelli et al. 1989) www.astro.princeton.edu

  6. Other nearby galaxies • LMC: Smaller bump and steeper rise into the UV (Nandy et al. 1981) • SMC: No bump, well fitted by A(λ)  1/ λ (Prevót et al. 1984) • M31: Average Galactic extinction law (Bianchi et al. 1996) Graph from Pei (1992) www.astro.princeton.edu

  7. Why measure higher redshift extinction curves? • From the four examples we know, we see that extinction curves can vary greatly • When analysing data where extinction needs to be accounted for the galactic extinction curve is frequently assumed • Examine if dust, and hence extinction, varies with z and galaxy type • So, how do we do it? www.astro.princeton.edu

  8. HIGH-z EXTINCTION CURVES www.astro.princeton.edu

  9. High-z Extinction - GRBs The intrinsic powerspectrum of the GRB is described by a powerlaw (or a broken powerlaw) Deviation from the slope is due to absorption along the line of sight www.astro.princeton.edu

  10. High-z Extinction - GRBs • Typically SMC extinction (e.g. Jakobsson et al. 2004, Kann et al. 2005) • A detection of the 2175 bump at z=2.45 • Can we locate tracers of the bump? • Metallicity? - No. • UV radiation field - CI lines (talk by Malesani)? • Dust to gas ratio? (Kann et al. 2005) (ÁE et al. 2009) www.astro.princeton.edu

  11. High-z Extinction - Lenses • Compare two images, where ideally one should suffer no extinction and the other go through the galaxy • For more than doubly imaged quasars have the possibility of getting more than one curve for the lensing galaxy • Optimized for redshifts z=0-1 - future surveys will reach z2-3 www.astro.princeton.edu

  12. High-z Extinction - Lenses • SBS 0909+532 • Double • zl = 0.83; zQ = 1.38 • Extinction: • E(B-V) = 0.21 ± 0.02 • RV = 2.1 ± 0.9 • A(V)  0.44 • Strong detection of the 2175 Å bump (Motta et al. 2002) www.astro.princeton.edu

  13. Extinction along both lines of sight • Method measures a differential extinction curve Galactic extinction: www.astro.princeton.edu

  14. Extinction along both lines of sight The deviation of the real RV to the deduced RVdiff is given by , where: (ÁE et al. 2006) Does NOT give a large systematic bias for mean RV values! www.astro.princeton.edu

  15. VLT Survey • 10 systems, (5 doubles and 5 quads) • Broad wavelength coverage (U,B,V,R,I,z’,J,H,Ks ) • 3 late type, 7 early type galaxies • Lens redshift zl=0.04-1.01 www.astro.princeton.edu

  16. High-z Extinction - Lenses • B1152+199 • Double • Late type galaxy • zl = 0.44; zQ = 1.02 • Extinction • RV = 2.1 ± 0.1 • A(V) = 2.43 ± 0.09 (ÁE et al. 2006) www.astro.princeton.edu

  17. High-z Extinction - Lenses • MG0414+0534 • Quad • Early type • zl = 0.96; zQ = 2.64 • Extinction (for both A2-B and A2-C): • A(V) = 0.9 ± 0.1 • RV = 2.7 ± 0.2 (ÁE et al. 2006) www.astro.princeton.edu

  18. High-z Extinction - Lenses • HE 0512-3329 • Double • Late type galaxy • zl = 0.93; zQ = 1.57 • Extinction • A(V) = 0.14 ± 0.04 (for MW extincton) • RV = 1.7 ± 0.4 (ÁE et al. 2006) www.astro.princeton.edu

  19. Dust to gas ratios (Dai+Kochanek 2009) (ÁE et al. 2009) www.astro.princeton.edu

  20. Redshift dependence? • See no strong correlation between extinction properties and redshift in our sample • Find (but beware small number statistics!): • RV=2.3 ± 0.5 (late type) • RV=3.2 ± 0.6 (early type) www.astro.princeton.edu

  21. Future Surveys • SNAP and LSST are proposed space/ground telescopes • Both missions will provide an extensive sample to study extinction and its evolution with redshift SNAP LSST Compared to 10 systems in the VLT survey! www.astro.princeton.edu

  22. Ideal LSST data z=2 z=1 z=0 www.astro.princeton.edu

  23. Goals • Measure typical reddening (E(B-V)) • Gives a lower limit • Measure the steepness of the slope (RV) • Independent measurement of dust extinction • Measure the frequency of the 2175 bump • Can we find tracers for the bump? • Is the bump created or destroyed? • Find trends with galaxy type and z • Follow-up? PAH emission? Dust to gas ratio? Column densities? www.astro.princeton.edu

  24. Find low RV: Not (yet) sensitive to the presence of the bump Affects estimates of w, systematic error 0.02-0.08 (Howell et al. 2009) High-z Extinction - Sne Ia • (Folatelli et al. submitted) • (Wang et al. 2008) www.astro.princeton.edu

  25. High-z Extinction - SNe Ia • Lower RV values - SNe Ia environments systematically different? (Branch & Tammann 1992, Krisciunas et al. 2000) • Extinction estimates might be affected by circumstellar dust (Wang 2005) • “Normal” RV values for not-heavily reddened SNe Ia (Folatelli et al. submitted) • (Folatelli et al. submitted) (Wang 2005) www.astro.princeton.edu

  26. High-z Extinction - Galaxies I • Starburst galaxies - “local” (Calzetti et al. 1994) • No 2175 bump • Grayer dust (larger RV) • Lyman-break galaxies at 2<z<4 (Vijh et al. 2003) • SMC type of extinction • Massive starforming galaxies (Noll et al. 2007, 2009) • 30% display significant 2175 bump (Noll et al. 2009) (Calzetti et al. 1994) www.astro.princeton.edu

  27. High-z Extinction - Galaxies II • Dust lanes in ellipticals: • RV values slightly lower than for the MW • 2.1<RV<3.3 (Goudfrooij 1994) • 2.03<RV<3.46, <RV>=3.02 (Patil et al. 2007) • 1.9<RV<4.1, <RV>=2.80.4 (Finkelman et al. 2008) (Patil et al. 2007) www.astro.princeton.edu

  28. High-z Extinction - QSO • Compare either individual or composite spectra with an unreddened mean spectra • Stacked spectra show no evidence of a 2175 bump (York et al 2006, Ménard et al. 2008) - although it could still be present in up to 30% of the lines of sight • The 2715 bump has been found in a few individual spectra (Wang et al. 2004, Srianand et al. 2008, Noterdaeme et al. 2009) • Can be confused with emission line features in the QSO itself (Noterdaeme et al. 2009) (York et al. 2006) (Srianand et al. 2008) www.astro.princeton.edu

  29. Discussion points? • Do we expect extinction properties to vary with z? How? • Will the uncertainty in extragalactic extinction estimates seriously hamper future cosmological surveys? Can we get a better handle on the possible bias? • The 2175 bump is present early on in the Universe - but what are its carriers and environment? • Is the dust around SNe different? www.astro.princeton.edu

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