Dark Cosmology Centre · 2006. 10. 25. · Dark Cosmology Centre Dark Cosmology Centre Summary...
Transcript of Dark Cosmology Centre · 2006. 10. 25. · Dark Cosmology Centre Dark Cosmology Centre Summary...
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen www.dark-cosmology.dk
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Extinction Curves of Lensing Galaxies
Árdís ElíasdóttirDark Cosmology Centre
Niels Bohr Institute, Univ. of Copenhagen([email protected])
Jens Hjorth (DARK)Sune Toft (Yale, ESO)
Ingunn Burud (Norwegian Meteorological Institute)Danuta Paraficz (DARK, NOT)
UC Berkely Cosmology Seminar - 24st of October 2006
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Contents
• Introduction• Extinction curves for higher redshift
galaxies• Extinction curves from lensed QSOs
– Method– Previous results
• VLT survey and results• Future prospects
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INTRODUCTION
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Lensing• The bending of light
due to the presence ofmatter along the line ofsight
• The lens equation:
!
s =Ds
Dl
r "Dls
ˆ #
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Extinction curves
• Measure the differencein emitted and observedlight
• Caused by interstellardust
• Traditionally measuredby comparing two starsof the same spectraltype
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The Galactic Extinction Curve
• Bump at 2175 Å (4.6 µm-1)
• RV : Ratio of total to selectiveextinction in the V band
• Mean value is RV = 3.1 (blue)
• Low value: RV = 1.8 (green) (Udalski2003)
• High value: RV = 5.6-5.8 (red)(Cardelli et al. 1989, Fitzpatrick et al.1999)
Galactic Extinction - empirically determined:– <A(λ)/A(V)> = a(λ-1) + b(λ-1)/RV (Cardelli et al. 1999)
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Other nearby galaxies
• LMC: Smaller bump andsteeper rise into the UV(Nandy et al. 1981)
• SMC: No bump, wellfitted by A(λ) ∝ 1/ λ(Prevót et al. 1984)
• M31: Average Galacticextinction law (Bianchi etal. 1996)
Graph from Pei (1992)
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HIGHER REDSHIFT EXTINCTION CURVES
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Why measure higher redshiftextinction curves?
• From the four examples we know, we seethat extinction curves can vary greatly
• When analysing data where extinction needsto be accounted for the galactic extinctioncurve is frequently assumed
• Dust behaviour, and hence extinction,expected to vary with z
• So, how do we do it?
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(York et al. 2006)
Extinction curves from QSOs
• Compare the composite spectraof quasars (DLAs, absorbers,galaxies) to a standard spectra
• Varying results– DLAs
• Extinction (Pei et al. 1992)• No extinction (Murphy & Liske
2004, Ellison et al. 2005)
– Mg II absorbers• Galactic extinction (Malhotra 1997)• SMC extinction (York et al. 2006)
– Foreground galaxies• Galactic type extinction (Östman et
al. 2005)
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Extinction curves from GRBs
• Found bystudying thespectral energydistribution
• Seem to favourSMC typeextinction(Jakobsson etal. 2004, Kannet al. 2005)
(Kann et al. 2005)
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Extinction curves from SNe Ia
• Consistent with Galacticextinction (Riess et al.1996)
• Lower RV values - SNe Iaenvironmentssystematically different?(Branch & Tammann1992, Krisciunas et al.2000)
• Extinction estimatesmight be affected bycircumstellar dust (Wang2005)
(Wang 2005)
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EXTINCTION CURVES FROM LENSED QSOs
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The Method
• Compare two images, where ideally one should sufferno extinction and the other go through the galaxy
• For more than doubly imaged quasars have thepossibility of getting more than one curve for thelensing galaxy
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Extinction along both lines of sight
!
Adiff(") = A
B(") # AA
(")
= EB# E
A( ) RVdiff a("#1) + b("#1)[ ]
!
RVdiff
RVB
= 1+E
A/E
B
1" EA/E
B1"
RVA
RVB
#
$ %
&
' (
) 1+*
!
E " E(B #V ) = A(B) # A(V )( )
Galactic extinction:
The deviation of thereal RV to thededuced RV
diff isgiven by η, where:
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Extinction alongboth lines of sight
RV=2.0 (lower E(B-V))
RV=4.0 (higher E(B-V))
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Microlensing
• The lensing by stars or other objects in the lensgalaxy
• Affects the continuum part of the emission• Effects can look like ‘extinction’• If the data are taken on a timescale smaller than
that of the microlensing signal, then any achromaticmicrolensing signal should, to first order, only affectthe estimate of the intrinsic magnitude ratio
• For chromatic microlensing, it is necessary to studythe spectra of the quasars to separate it from theextinction signal
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Time delays
• Travel path for different images differs ⇒intrinsic variations show up at different times
• Ideally one should take data with a timedifference corresponding to the time delay
• Alternatively, if data are taken simultaneously,then the intrinsic variations should only affectthe estimated intrinsic brightness ratio of theimages
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PREVIOUS STUDIES
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Falco et al. 1999• Studied the extinction of
23 lensing galaxies with0<z<1 by assuming amean Galactic extinctionlaw
• They did further analysison a few systems wherethey allowed RV to vary
• Note: Their data iscombined from epochsspanning several years
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Motta et al. (2002)
• SBS 0909+532• zl = 0.83• Strong detection of
the 2175 Å bump• RV = 2.1 ± 0.9• E(B-V) = 0.21 ±
0.02
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Muñoz et al. (2004)
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VLT SURVEY
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• 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
• Effort made to minimize time delay between observations
VLT Survey
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Correcting for microlensing
• Calculate the proportion of the continuum part tothe the full emission for each band
• Introduce a correction due to microlensing which isproportional to this ratio
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Extinction laws considered• Galactic extinction law
• Linear SMC type extinction
• Power law
!
A(") = A(V )"
5500Å
#
$ %
&
' (
)1
!
A(") = A(V )"
5500Å
#
$ %
&
' (
)*
!
A(") = A(V ) a("#1) + RVb("#1)[ ]
!
E(B "V ) = A(B) " A(V )
!
RV"
A(V )
E(B #V )
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RESULTS - INDIVIDUAL SYSTEMS
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B1152+199• Lens system
– Double– Late type galaxy– zl = 0.44– zQ = 1.02
• Best fit from a Galactic extinctionlaw with– RV = 2.1 ± 0.1– A(V) = 2.43 ± 0.09
• When the intrinsic ratio is fixed,the best fit gives– RV = 2.0 ± 0.1– A(V) = 2.41 ± 0.09– s = 0.32 ± 0.07
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HE0512-3329• Lens system
– Double– Late type galaxy– zl = 0.93– zQ = 1.57
• Linear extinction– Best fit– A(V) = 0.35 ± 0.02
• Galactic fit– A(V) = 0.14 ± 0.04– RV = 1.7 ± 0.4
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MG0414+0534• Lens properties
– Quad
– Early type galaxy
– zl = 0.96; zQ = 2.64
• Similar goodness of fits
• Galactic extinction - A2-B:
– A(V) = 0.87 ± 0.05
– RV = 2.7 ± 0.2
• Galactic extinction - A2-C:
– A(V) = 0.91 ± 0.04
– RV = 2.6 ± 0.1
• The similar properties derived fromcomparing to B and C suggest that theirextinction does not affect the result
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RESULTS - FULL SAMPLE
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Parameters of the fits
• Mean RV is:– RV = 2.8 ± 0.3 (full sample)– RV = 2.8 ±0.4 (‘golden’ sample)
• Mean A(V) = 0.54 (Galacticextinction)
• See no correlation betweenA(V) and RV
• Strong anti-correlationbetween RV and α
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Preferred extinction
• The sample as awhole does notshow a preferencefor a certainextinction law
• Individual systemscan show a strongpreferenceGalactic: blue cross
Power law: green starLinear law: red diamond
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Extinction vs. redshift and type
• See no strongcorrelation betweenextinction properties andredshift in our sample
• Find (but beware smallnumber statistics!):– RV=2.3 ± 0.5 (late type)
– RV=3.2 ± 0.6 (early type)
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FUTURE PROSPECTS
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Future prospects
• Method is ideal for studying dust extinctionof high redshift galaxies
• Can complement various cosmologicalprobes, where dust correction is crucial (e.g.SN Ia studies)
• Ideal for studying evolution of dustproperties in the redshift range of 0 < z < 1
• Need a larger sample to make statisticallyrobust claims
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What’s required?
• To increase sample size, need higher resolution ->space based observations
• Effects of extinction along both lines of sight reducedfor a large sample
• Use galaxy-galaxy lenses?
• Want multiband observations in the optical and theinfrared
• A simultaneous radio survey, to constrain the intrinsicratio, would be very useful
• Can SNAP be of use?
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SNAP prospects
• SNAP has 9 filters, 6optical and 3 IR, fromλ≈450-1500 nm
• Will provide anextensive sample tostudy extinction and itsevolution with redshift
100-100050.000Wide (WL)
~105.000Deep (SNIa)
QuasarGalaxy(Marshall etal. 2005)
(Krisciunas et al. 2006)
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Summary• Multiply imaged quasars can be used to study the
extinction curves of lensing galaxies• Extinction along both lines of sight can affect single
systems, but partially cancels out in a large sample• Our mean RV = 2.8 ± 0.3 is slightly lower than, but
consistent with, that of the Galaxy (RV = 3.1)• We see no strong correlation between extinction
properties and redshift• A larger sample size is needed to make statistically
robust claims -> space based survey of greatinterest -> a SNAP ‘piggy-back’ survey?