2012/11/30

減光曲線から探る星間ダストの多様性(Variation of interstellar dust
probed by extinction curves)
野沢 貴也 (Takaya Nozawa)& 福来 正孝 (Masataka Fukugita)(Kavli IPMU, University of Tokyo)

1. Extinction curve
I0

I0 exp[-τλ]I0(1-exp[-τλ])Extinction curve: wavelength-dependence of extinction
caused by interstellar dust grains
・ essential for knowing theintrinsic SEDs of galaxies

Whittet 2003

・ depends on physical andoptical properties of dust

2. Interstellar dust models in MW〇 MRN dust model (Mathis, Rumpl & Nordsieck 1977)・ dust composition : graphite & silicate (Mg1.1Fe0.9SiO4)・ size distribution : power-law distributionn(a)da ∝ a^{-q}da with q = 3.5, 0.005 μm ≤ a ≤ 0.25 μm〇 WD01 model(Weingartner & Draine2001)

・ dust composition :silicate + graphite +PAHs

Optical constants:
Draine & Lee (1987)

・ size distribution :power-law withexponential decay +lognormal
0.3 nm ≤ a ≤ 1 μm

2. Interstellar dust models in MW〇 MRN dust model (Mathis, Rumpl & Nordsieck 1977)
・ dust composition : graphite & silicate (Mg1.1Fe0.9SiO4)・ size distribution : power-law distributionn(a)da ∝ a^{-q}da with q = 3.5, 0.005 μm ≤ a ≤ 0.25 μm〇 WD01 model(Weingartner & Draine2001)

・ dust composition :silicate + graphite +PAHs

Optical constants:
Draine & Lee (1987)

・ size distribution :power-law withexponential decay +lognormal
0.3 nm ≤ a ≤ 1 μm

3. CCM relationship and RV・ essential for knowing the
intrinsic SEDs of galaxies

VB・ depends on physical andoptical properties of dust

Fitzpatrick & Massa (2007)〇 CCM relation (Cardelli, Clayton, & Mathis 1989)
・ Aλ/AV = a(x) + b(x) / RV, where x = 1 / λ・ RV : ratio of total-to-selective extinction
RV = AV / (AB – AV) = 1 / (AB/AV – 1) cf. RV,ave = 3.05–3.10

4. Variety of interstellar extinction curves
・ There are a large variety of interstellar extinction curves
・ How much can the properties of dust grains be changed?
gray curves:
328 extinction curves
derived by Fitzpatrick& Massa (2007, FM07)
red bars:
1σ ranges including
224 dataOur goal is to find the dustblue
properties
bars:
that satisfy these extinction2σranges
ranges including
312 data

5. Comparison between FM07 and CCM89
UV-through-IR extinction curves

Close-up of IR extinction curves

black: 1σ range of the FM07 data
red: CCM curve with Rv = 2.75
blue: CCM curve with Rv = 3.60
green: extinction curve for thecase of Rv=3.1 by WD01
fully consistent in UV region

Results from CCM formula withRv = 2.75-3.60 are 0.02-0.06 maghigher than the 1σ range in JHK
WD01 model is based on resultby Fitzpatrick (1999), which issimilar to CCM curve w/ Rv=3.1

6. Dust model(spherical grain)

・ power-law size distribution (amin < a < amax)

amin = 0.005 um (fixed)
q and amax : parameters (same for all grain species)fi,j ➔ a fraction of an element i locked up in a grain j
Solar abundance: Grevesse & Sauval (1998)
all of Fe (and Mg and Si) are locked in dust grains

・ grain species considered in this paper－graphite, glassy carbon, amorphous carbon, SiC－astronomical silicate (MgFeSiO4), Mg2SiO4－Fe, Fe3O4, FeS

7. Illustration of contour plots
1σ range of FM07 data

UVUBJHK

The 1σ ranges from FM07 data
are classified into three groups
UV: UV bump (0.22 μm), FUV dip(0.16 μm), FUV rise (0.125 μm)
UB: U band and B band
JHK: J band, H band, K band

7-1. Contour plots for fgra/fsil = 1.0
Case of 1σ data, fgra/fsil = 1.0

Case of 1σ data, fgra/fsil = 1.0

contour plots of amax and q that
fulfill the 1σ range of FM07 datafor fgra/fsil = 1.0 (Mgra/Msil = 0.78)
blue: constraint from UV/FUV
green: constraint from UB band
red: constraint from JHK band

contour plots of amax and q that
fulfill the 1σ range of CCM result
for fgra/fsil = 1.0 (Mgra/Msil = 0.78)
blue: constraint from UV/FUV
green: constraint from UB band
red: constraint from JHK band

7-2. Contour plots for fgra/fsil = 0.5
Case of 1σ data, fgra/fsil = 0.5

Case of 1σ data, fgra/fsil = 0.5

contour plots of amax and q that
fulfill the 1σ range of FM07 data
for fgra/fsil = 0.5 (Mgra/Msil = 0.39)
blue: constraint from UV/FUV
green: constraint from UB band
red: constraint from JHK band

contour plots of amax and q that
fulfill the 1σ range of CCM result
for fgra/fsil = 0.5 (Mgra/Msil = 0.39)
blue: constraint from UV/FUV
green: constraint from UB band
red: constraint from JHK band

7-3. Contour plots for fgra/fsil = 0.2
Case of 1σ data, fgra/fsil = 0.2

Case of 1σ data, fgra/fsil = 0.2

fC,gra > 0.25

contour plots of amax and q that
fulfill the 1σ range of FM07 datafor fgra/fsil = 0.2 (Mgra/Msil = 0.16)
blue: constraint from UV/FUV
green: constraint from UB band
red: constraint from JHK band

contour plots of amax and q that
fulfill the 1σ range of CCM result
for fgra/fsil = 0.2 (Mgra/Msil = 0.16)
blue: constraint from UV/FUV
green: constraint from UB band
red: constraint from JHK band

8-1. Piled-up contour for graphite-astro.sil
In this study,NH/E(B-V) =(5.7±1.7)x1021 cm3/mag(Gudennavar et al. 2012)

fC,gra > 0.56

Values of q and amax that meetthe 1σ range of FM07 data are
confined to be narrow ranges

3.2 < q < 3.7
0.19 um < amax < 0.34 um

In previous studies,NH/E(B-V) = NH/(AB-AV)= 5.8x1021 cm3/mag(Bohlin et al. 1978)

8-2. Piled-up contour for carbon-astro.sil

amorphous C ➔ up to ~60 %glassy C ➔ up to ~50 %SiC ➔ up to ~15 %more than 40 % carbon areneeded to be locked in graphite

Dashed line (fC, grain = 0.7)
・ gra-asil (fC, gra /fC, grain = 1.0)
・ gra-aC-asil (fC, aC /fC, grain = 0.3)
・ gra-gC-asil (fC, gC /fC, grain = 0.3)
・ gra-SiC-asil (fC, SiC /fC, grain = 0.1)

8-3. Piled-up contour for carbon-astro.sil

Fe ➔ up to 100 %Fe3O4 ➔ up to ~80 %FeS ➔ up to 100 %many Fe atoms are not always
needed to be locked in silicate

Dashed line (fC, gra = 0.7)
・ gra-Fe-fore (fFe, Fe /fFe, grain = 1.0)
・ gra-Fe3O4-sil(fFe, Fe3O4 /fFe, grain = 0.8)
・ gra-FeS-sil (fS, FeS = 1.0)

9-1. Dust properties in SMC

Values of q and amax that meetthe extinction ranges in SMC areconfined to be narrow ranges

3.2 < q < 3.8
0.19 um < amax < 0.35 um

9-2. Dust properties in SMC
For SMC, NH/E(B-V) =(2.3±2.2)x1022 cm3/mag(Welty et al. 2012)
For MW, NH/E(B-V) =(5.7±1.7)x1021 cm3/mag

0.04 < fC,gra < 0.41

Values of q and amax that meetthe extinction ranges in SMC areconfined to be narrow ranges

3.2 < q < 3.8
0.19 um < amax < 0.35 um

SMC extinction curve can be
explained by the MRN model
without graphite (Pei 1992)

10. Summary
・ The observed ranges of NIR extinction from FM07
do not match with the results from the CCM formula➔ There is no combination of q and amax that satisfy
the observed ranges when CCM results are adopted
・ For graphite-silicate model, the values of q and amaxthat satisfy the 1σ extinction ranges are, respectively,－ 3.2 < q < 3.7 and 0.19 um < amax < 0.34 um
0.56 < fC,gra < 1.0 for MW－ 3.2 < q < 3.8 and 0.19 um < amax < 0.35 um
0.04 < fC,gra < 0.41 for SMC

・ ~30 % of graphite can be replaced with amorphous
carbon and glassy carbon
・ Most of Fe atoms can be locked in Fe, Fe3O4, and FeS