ALMAで見るz>6の銀河のダスト進化
Hiroyuki Hirashita (平下 博之)
Wei-Chen Wang
Kuan-Chou Hou(ASIAA, Taiwan)
Wang et al. 2017, MNRAS,465, 3475

Submm Observation

Tdust = 42 K
LIR = 1.4 × 1012 L!

ALMA bands are
suitable for high redshift.

Detection limits:
100 arcmin2 survey with 500 h(Y. Tamura)

850 µmCosmic Infrared Background
Dole et al.

Dust emission is as
important as stellar
optical emission instar formation
activities of galaxies.

Fujimoto et al. (2016)

CIB sources at 1.2 mm have been
almost resolved into sources.

Toward Galaxies in the
Epoch of Reionization(z > 6)

LBG at z = 7.5 Detected by ALMA
Watson et al. (2015)at z = 7.5 (lensed LBG)

Stellar mass ~ 2×109 M!
SFR ~ 10 M!/yr

LBGs at High z
Bouwens et al. (2016)

Mostly not detected even by
ALMASource of Dust at z > 6
Mancini et al. (2015)
Watson et al. (2015)

Dust growth byaccretion in the dense
ISM is important forthe z = 7.5 galaxy.

3. Dust Enrichment at High Redshift
Gas
Metal i“Chemical evolution model” of galaxies
Gas ⇒ Star ⇒ metal/dust injection
SFSupply from stars
ψ = Mgas/τSFDustζSN = τSN/τSFζacc = τacc(Zsun)/τSFfin

SF Destruction by Growth in clouds
SNe ~ 108 yr τacc ∝ D/(nZ)Analysis Using Dust Evolution Model
Wang, Hirashita & Hou (2016)(1) One-zone model including dust formation (stellarsources + accretion) and destruction (SNe).
(2) Dust emission is calculated consistently with the stellar
radiation field and dust mass.
ζSN = τSN/τSFζacc = τacc(Zsun)/τSFfin

Constraint from the z = 7.5 LBG
Wang, Hirashita, & Hou (2016)

Accretion time-scale

Additional constraint
Z < 0.1 Zsun

Destruction time-scale

Standard for nearby galaxies.

Constraint from the z = 7.5 LBG
Wang, Hirashita, & Hou (2016)

Accretion time-scale

By allowing for metal-rich solutions

Destruction time-scale

Standard for nearby galaxies.

ALMA Detection of LBGs at z > 6Requires…
Wang, Hirashita, & Hou (2016)(1) Very efficient grain growth by accretion (10–100 times
more efficient than nearby galaxies) if their metallicities
are <~ 0.1 Z! (Mancini et al. 2015);(2) They are solar-metallicity objects; or(3) Very high condensation efficiency in stellar ejecta.

Toward SKA (Era)(1) Deeper ALMA observations.
(2) Development of dust evolution models and radiationtransfer codes. → Escape fraction of ionizing photons.
(3) Relation with gas components ([C II], [O III], CO).
Theoretical modeling

Relation to H I.

Inoue et al. (2016)

Thank you.

SFR Traced by Dust Emission
TotalIRUV

Burgarella et al. (2013)
See also Takeuchi et al. (2005)

Star formation
rate traced by FIR
dust emission
becomes moreand moreimportant as wego to the epoch ofSFR peak.

A Lot of Dust at z > 5(109 yr after the Big Bang)
Quasars

age < 1 Gyr

Bertoldi et al. (2003)

Michałowski et al. (2010)

LBGs at z ~ 6
Willott et al. (2015)

Color: [C II] 158 µm, Contour: dust continuum
Cross: center of NIR

Poor Dust Content in Lyα Emitters
Ouchi et al. (2013)
Strong upper limit
put by ALMA
(Ouchi et al. 2013)“Himiko”
Giant Lyα Emitterat z = 6.6(age ~ 100–300Myr)

5.4 kpc

Inefficient FIR emission compared with nearby galaxies.

LBGs at z = 5–6
Indicator of total dust absorption

Capak et al. (2015): z = 5–6

Steeper extinction curve

4/9 typical (1–4L*)LBGs aredetected by ALMA
intrinsic SED slope
Indicator of reddening by dust