銀河進化とダスト 平下 博之 (H. Hirashita) （筑波大学）

1.Importance of Dust in Galaxies 2.Evolution of Dust Amount 3.Importance of Size Distribution 4.Toward Complete Dust Model 5.Summary and Plan 内容

1. Importance of Dust in Galaxies M33: Hinz et al. (2004) Optical (B-band): stars FIR (70  m): dust

Radiative Processes (0.1 – 3  m) UV, opt, NIR (10 – 1000  m) MIR, FIR, sub-mm Dust grain a < 1  m T ~ 10 – 1000 K Si 化合物、 C などから なると考えられている。 extinction reemission

Spectral Energy Distribution of Nearby (z ~ 0) Galaxies FIR : 50 – 300  m Schmidt et al. (1997)

What to Quantify for Grains (1) Amount of grains: M dust (2) Properties of grains a.Species (Silicate, Graphite, …) b.Size (a ~ 10 Å – 1  m)  ~ (  dust /  a 3 ) a 2 Q

2. Evolution of Dust Amount (1) Dust is supplied by Type II SNe (m * > 8 M sun ). (2) Dust per SN = 0.4 M sun (Todini & Ferrara 2001). (3) Dust destruction is considered (not efficient). SFR (t) ⇒ SN II rate (t) ⇒ M dust (t) (Salpeter IMF) Given next Hirashita & Ferrara (2002) We concentrate on young (t < 1 Gyr) galaxies.

Star Formation Law: SFR(t) Star formation is deeply related to the abundance of molecular gas (the main coolant) SFR = (molecular gas mass)/(dynamical mass) = f H 2 M gas /  dyn chemical reaction network dust H 2 formation on dust included Determined for (M vir, z form | cosmology) Self-consistent treatment of dust, H 2, and SF!

Dust-Induced Transition!? Transition molecular clouds Dust supply Primeval ISM Evolved ISM Dust-polluted galaxies H 2 formation on dust: H + H + grain → H 2 + grain Primeval (dust-clean) galaxies H 2 formation in gas phase: H + e - → H - H - + H → H 2 + e –

Star Formation History z form = 10 M vir = 10 9 M sun 4  dyn dust H 2 formation on dust

FIR luminosity becomes comparable to the UV luminosity. FIR/UV luminosities UV luminosity FIR luminosity z form = 10 M vir = 10 9 M sun 4  dyn

Test of Our Model for z > 5 Sub-mm (ALMA) near infrared (JWST) A high-z galaxy

Number Counts (z > 5) 5  limit for 8 h 3  limit for 10 5 s ALMAJWST

3. Importance of Size Distribution A(/A(B)A(/A(B) Pei (1992) Extinction Curve （吸収の波長依存性） ダストの光学特性 サイズ分布

Cross Section of Grains Different size = Different optical properties Mie Theory: 複素屈折率 m a x ≡ 2  a / dN(a) / da ∝ a –3.5 for Milky Way (Mathis et al. 1977)

Dust Size Distribution of SNe Nozawa et al. (2003)

Hirashita et al. (2005) Extinction Curves of SNe II Maiolino et al. (2004) for a QSO at z = 6.2

IR Dust Emission Takeuchi et al. (2005)

Interstellar Medium Metals Dust Growth in Clouds Inclusion into Stars Destruction by Shocks Extinction Far-Infrared Radiation 4. Toward Complete Dust Model

Processes of Dust Destruction (1) Sputtering a.Thermal b.Nonthermal B (2) Shattering ダストのサイズ分布は (2) により大きく変わる (Jones et al. 1996) 。

Basic Ingredients for Modeling (1)Crater formation and disruption ( , P cr ) (2)Size distribution of fragments ( ∝ a –3.3 ) Jones et al. (1996) Acceleration by compression drags

Effects of Shattering Initial n(a) ∝ a –3.5 n = 0.25 cm –3 T = 10 4 K B = 3  G 1 SN passage

(1) Dust determines how galaxies look like (e.g., SED). ← Extinction and infrared emission. (2) Based on evolution of dust amount, we have predicted sub-mm and NIR number counts in future survey: ALMA, JWST, Herschel, SPICA, … (3) But grain size distribution is also very important! a. Extinction curve (consistent with SN production) b. Infrared SED (4) We are now developing dust destruction scheme. Shattering can be treated at this stage: a. Inclusion into my previous one-zone model b. Inclusion into hydrodynamical simulation 5. Summary and Plan