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 Department of Astrophysical Science, Princeton University www.astro.princeton.edu

Outline Local extinction curves High-z extinction curves GRBs Lenses SNe Galaxies QSOs Department of Astrophysical Sciences www.astro.princeton.edu

LOCAL EXTINCTION CURVES Department of Astrophysical Sciences www.astro.princeton.edu

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 Department of Astrophysical Sciences www.astro.princeton.edu

The Galactic Extinction Curve “Reddening” (Cardelli et al. 1989) 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? Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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? Department of Astrophysical Sciences www.astro.princeton.edu

HIGH-z EXTINCTION CURVES Department of Astrophysical Sciences www.astro.princeton.edu

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 Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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 Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

Extinction along both lines of sight Method measures a differential extinction curve Galactic extinction: Department of Astrophysical Sciences www.astro.princeton.edu

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! Department of Astrophysical Sciences www.astro.princeton.edu

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 Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

Dust to gas ratios (Dai+Kochanek 2009) (ÁE et al. 2009) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

Future Surveys Quasar 4000 Supernova 500 SNAP LSST Galaxy Quasar 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 (Marshall et al. 2005) Galaxy Quasar Deep (SNIa) 5.000 ~10 Wide (WL) 50.000 100-1000 Quasar 4000 Supernova 500 Compared to 10 systems in the VLT survey! Department of Astrophysical Sciences www.astro.princeton.edu

Ideal LSST data z=0 z=1 z=2 Department of Astrophysical Sciences www.astro.princeton.edu

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? Department of Astrophysical Sciences www.astro.princeton.edu

High-z Extinction - Sne Ia 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) (Folatelli et al. submitted) (Wang et al. 2008) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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) Department of Astrophysical Sciences www.astro.princeton.edu

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? Department of Astrophysical Sciences www.astro.princeton.edu