Cosmic Dust Enrichment and Dust Properties Investigated by ALMA Hiroyuki Hirashita ( 平下 博之 ) (ASIAA, Taiwan)

1.What Is “Known” about Galaxy Dust? 2.Dust Enrichment (Especially at High-z) 3.More Detailed Look (Low-z) 4.Summary Topics To stimulate your idea!

1. What Is “Known” about Galaxy Dust?

Dust Extinction in the Milky Way Lund Observatory Optical ( ~ 0.5  m) Scattering + Absorption (= Extinction) of stellar light by dust grains

Grain size distribution N dust (a) ∝ a  with  m < a < 0.25  m Mathis et al. (1977) Extinction Curve Extinction (absorption+scattering) as a function of i: grain species (silicate, graphite)  a 2 Q (a): grain cross section (1) Only applicable for very nearby galaxies. (2) Evidently ALMA bands cannot do this. opticalUV

Milky Way in Far Infrared COBE 140  m Thermal emission from dust

Désert et al. (1990) Large grains (LGs) in radiative equilibrium with the interstellar radiation field Excess by very small grains (VSGs) Wavelength (  m) Intensity 140  m Properties of Far-Infrared (FIR) Spectral Energy Distribution (SED) FIR sub-mm

Merits/Demerits of FIR  Submm (1)SED is simple: I = C  B (T dust ) (+) a few wavelengths are enough to observe ( - ) very limited information on dust material (  ) (2) Depends on T dust (+) good tracer of the interstellar radiation field (star formation activity) ( - ) a single wavelength observation is not enough ( ⇒ collaboration with AKARI, Spitzer, Herschel) (3) grain size << in FIR-submm ⇒ mass absorption coefficient is independent of grain size ( - ) no information for the grain size (+) good tracer of grain amount

Dust in Cosmological Context NASA Metals (→ solid = dust) H, He, Li C, N, O, …, Fe Nucleosythesis in the Universe Beginning of Metal (dust) Production Grasp of “primeval galaxies” in the Universe ＝ Understanding of the initial metal/dust enrichment Dust already existed at z ~ 6 (Bertoldi et al. 2003). t

Sub-mm for High-z Dust ALMA bands are suitable for high redshift. Detection limits: 100 arcmin 2 survey with 500 h (Y. Tamura) 850  m T dust = 42 K L IR = 1.4 × L 

2. Dust Enrichment (Especially at High- z ) The dust enrichment in the local Universe is already complicated (formation from supernovae, AGBs,..., growth in interstellar clouds, destruction by shocks, etc.) High-redshift (z > 5) is simpler (formation/destruction by supernovae is dominated)!

Ly  Emitter One of the young populations found at the highest z. Observational indication of dust E(B  V) =  0.32 (Finkelstein et al. 2009)  0.3 (Pirzkal et al. 2007) Iye et al. (2006) Kashikawa et al. (2006)

Possible to Detect Early Dust Enrichment in the Universe? (1) Modeling of dust enrichment in LAEs. (2) Estimate of the FIR/sub-mm flux from a LAE. (3) Detectability by ALMA. Detectability of the first dust enrichment in the Universe

Theoretical Framework Dayal, Hirashita, & Ferrara (2009) GADGET homepage (Springel 2005) Cosmological SPH simulation (75 h - 1 Mpc) 3 ⇔ 2000 arcmin 2 Dust enrichment and destruction by supernovae to obtain M dust for each galaxy.

L IR Estimation for Each Galaxy Optical depth of dust for stellar UV light:  UV = 3  dust /(4as)  dust = M dust /(  R 2 ) Escape fraction of UV continuum f c = [1  exp( -  UV )]/  UV FIR luminosity L FIR = (1  f c )L UV 0 Dust temperature and SED L = 4  M dust  B (T dust ) FIR (sub-mm) flux f = (1 + z)L (1 + z) /(4  d L 2 ) Dust size a = 0.05  m Material density s = 2.3 g/cm 3

ALMA Observation Strategy 850  m is the most suitable. Blue: 850  m Green: 1.4 mm Red: 3 mm Dayal, Hirashita, & Ferrara (2010) lines: detection limits with 1 hour integration (full ALMA) Early dust formation by stars (supernovae) can be quantified.

3. More Detailed Look (Low- z )

Combination with FIR Hirashita & Ichikawa (2009) 140  m / 100  m flux ratio I = C  B (T dust ) FIR data by AKARI, Spitzer, and Herschel help to estimate T dust. 60  m / 100  m flux ratio high dust temperature Large range of dust temperature traced in FIR.

“Embedded” Cold Dust Shielded from Stellar Radiation Hirashita & Ichikawa (2009) (1)  UV ↑ (shield) ⇒ cold dust↑ (2) radiation field↑ ⇒ T dust ↓ Sub-mm can distinguish the difference. increase of cold dust

4. Summary I: Early Cosmic Dust Enrichment (1) Early production of dust by stars a.How much dust forms in stars? b.Prediction by nucleation theory (e.g., Nozawa et al. 2003) is correct? (2) How fast? ( ⇒ Evolution of dust optical depth ⇒ reionization) (3) Connection with the planet formation? What should theory do? Predict as many (global) quantities which dust concerns. ex. reionization, molecular hydrogen abundance, luminosity function from UV to FIR

II: Detailed Look of Nearby Galaxies (1) Shielded (embedded) dust a.Physical condition of dust grains in star-forming galaxies (especially the optical depth) b.Geometry of dust distribution (2)  (silicate/graphite ~ 2; some amorphous ~ 1  1.5) (3) Combination with AKARI, Spitzer, and Herschel is crucial.