2015/06/05

Ia型超新星の特異な減光則から探る
系外銀河のダスト特性
野沢 貴也 （Takaya Nozawa）
National Astronomical Observatory of Japan

1-1. MW extinction curve and CCM relation
small size

Rv = 2.2~5.5
RV,ave ~ 3.1〇 CCM relation(Cardelli, Clayton, Mathis 1989)

RV : ratio of total-toselective extinction
RV = Av / E(B - V)
= AV / (AB – AV)large size

Data: Fitzpatrick & Massa (2007)

Aλ/AV = a(x) + b(x) / Rv
where x = 1 / λ‐steeper extinction curve (lower Rv) ➜ smaller grains‐flatter extinction curve (higher Rv) ➜ larger grains

1-2. Extinction law towards Type Ia SNe○ Type Ia supernovae (SNe)‐ thermonuclear explosion of WD- single-degenerate scenario (WD + MS)- double-degenerate scenario (WD +WD)
‐ main sources of cosmic Fe- MFe ~ 0.7 Msun (cf. MFe ~ 0.07 Msun in CCSNe)‐ discovered in all types of galaxies- star-forming, elliptical, irregular, etc …

Phillips+1993
Riess+1996‐ cosmic standard candles

MB = mB - 5 log10(DL) - AB - 5➜ Rv = 1.0 ~ 2.5to minimize the dispersion of Hubble diagram(e.g., Tripp+1998; Conley+2007; Phillips+2013)

Astier+2006

1-3. Other examples of extinction in galaxies○ Extinction of individual SNe‐ from the observed colors of SNe Ia
Rv ~ 3.2, similar to the Galactic value- a few outliers (SN 2005A, SN 2006X)
with Rv ~ 1.7 (Folatelli+2010)
Dong+2014○ Extinction of nearby galaxies‐ M 31 (Andromeda Galaxy)- disk region: Rv ~ 3.1 (Bianchi+1996)- dusty complex: Rv ~ 2.1 (Melchior+2000)- central parts: Rv ~ 2.4-2.5 (Dong+2014)‐ elliptical galaxies (Patil+2007)
Rv = 2.0-3.5 (with the average of Rv = 3.0)

➜ Rv is moderately low or normal
Patil+2007

1-4. Peculiar extinction towards SN 2014J○ Type Ia SN 2014J‐ discovered in M 82 (D ~ 3.5±0.3 Mpc)
- closest SN Ia in the last thirty years- highly reddened (Av ~ 2.0 mag)‐ reddening law is reproduced by CCM
relation with Rv ~ 1.4 (Ammanullah+2014)○ Origin of peculiar extinction‐ odd properties of interstellar dust
(Kawabata+2014; Foley+2014)‐ circumstellar dust (multiple scattering)(Wang 2005; Goobar+2008)➜ this scenario is unlikely(Maeda+2015; Johansson+2015)

Amanullah+2014

1-5. Aims of this talk1. もし本当にRv~1.5であったならば、銀河のSEDはどう影響されるか？

2. Rv~1.5を再現するような星間ダストモデルはあるのか？

2-1. Effects of low Rv on the SEDs
= 3000 K‐if Rv = 1.5, the SED for high TBB(TBB > 10000 K) is highly affected- (A2500A / Av) for Rv = 1.5~ 3 (A2500A / Av) for Rv = 3.1- (A1600A / Av) for Rv = 1.5~ 3.5 (A1600A / Av) for Rv = 3.1

2-2. Dependence of absorbed luminosity on Rv‐ for TBB > 6000 K, Rv = 1.5 absorb
stellar lights than Rv = 3.1‐ for TBB < 6000 K, Rv = 3.1 absorb
stellar lights than Rv = 1.5➜ Rv=1.5 curve is steeper than
Rv=3.1 curve at 0.5-1.0 µm

3-1. Dust model for Rv = 1.5 CCM curve〇 MRN dust model (Mathis, Rumpl, & Nordsieck 1977)- dust composition : silicate (MgFeSiO4) & graphite (C)- size distribution : power-law distributionn(a) ∝ a^{-q} with q=3.5, amax = 0.25 μm, amin = 0.005 μm

Rv = 1.5 curve ➜ amax = 0.085 µm, amin = 0.005 µm

3-2. Dust models for Rv = 1.0 and 2.0 curve

Rv = 1.0 curve ➜ amax = 0.055 µm, amin = 0.005 µm
Rv = 2.0 curve ➜ amax = 0.12 µm, amin = 0.005 µm
But, the values of Rv based on the MRN dust model are higher
than Rv used for the CCM relation
RV,CCM = 1.0 curve ➜ RV, dust = 1.5
RV,CCM = 2.0 curve ➜ RV, dust = 2.1

3-3. Range of amax from variation of MW ECs

1σ: Rv = 2.65-3.60
2σ: Rv = 2.51-4.62

Nozawa & Fukugita (2013)

Ranges of q and amax that meet the1σ range of FM07 data are confined
to be narrow ranges of
3.2 < q < 3.7

0.19 µm < amax < 0.34 µm

3-4. Dependence of extinction on grain size

- Low values of Rv = 1.5-2.0 can be reproduced by the MRN dust
model with amax = 0.055-0.12 µm- Rv < 1.4 is unlikely to be realized with the MRN dust model- Rv, as well as the shape of extinction curve, does not dependon amin as long as amin < 0.01 µm

4-1. Implication from dust evolution in galaxies
dust amount

grain size distribution
MRNAsano+2013, 2014; Nozawa+2015

Dust evolution model
predicts that there may
be a phase of a steep
extinction curve(but, the calculated Rv
is not necessarily low)extinction curve5. Summary of this talkWe explore the interstellar dust model to reproduce
extinction curve with low Rv as suggested for SNe Ia1) Some studies (mainly SNe Ia cosmology) suggest thatthe Rv value towards SNe Ia is generally low (Rv < 2.5)

2) The CCM curves with Rv = 1-2 can be fitted by the MRN
dust model (graphite & silicate) with amax = 0.05-0.15 µm(instead of amax = 0.25 for Rv = 3.1)
3) Within the framework of the MRN dust model, the low
values of Rv < 1.5 are not likely to be achieved