Dust and Molecules in primordial galaxies

F.-Xavier Désert, Lab. Astrophysique, Grenoble

Erik Elfgren, Dept. of physics, Lulea, Sweden

Early dust in the galaxy structure formation opens up the possibility that “Normal” but intense star formation occurred in the first large galaxies.Normal: molecular H

2 formation on dust.

Here, we focus on z = 20 to 5 “dark age” period, preceding the IR bright, star formation peak at z = 3-1

WMAPOne year

Temperature - PolarizationCorrelation: = 0.170.04

Bennett, et al., 2003, ApJSS

Early reionisation suggested by WMAP

● TE correlation at low l suggests Reionisation redshift of z

i= 15

● Pop III stars are likely the source of the UV ionizing radiation field

● Could also produce some dust that will disseminate in the intergalactic medium (SNe and stellar winds can expel matter from low mass galactic halos).

● UV and dust altogether make an infrared background, which is computed here, that can be constrained by FIRAS Cosmic Infrared Background.

● Elaboration on early works by e.g. Bond,Carr,Hogan '91

Dust Production and Destruction

• Assumes a fraction (~0.1) of the baryons consumed in stars re-emerges as dust. The UV background implies a baryon consumption rate (36 eV/ 7 MeV baryons for one UV photon)

• Empirical lifetime is introduced based on (limited) knowledge of the Milky Way (0.1 Gyr)

Comoving dust density evolution

Direct consequence from UV backgroundCen 2002, ApJ

Dust Opacity @1mm

In the (sub)mm mostly in ²

Dust temperature

Radiation field is much smaller than the CMBTdust >~Tcmb

is just above the CMB temperature

Submillimetre Background: Generic spectrum

353545857 217 143

Planck HFI bandpass

Planck (August 2007)should help find small scale structure of this submillimetre background.Component separation on HFI maps could yield an unambiguous trace of early dust in the reionization period.

Jenkins et al, 1998 ApJ, 499, 20

Need for N-body simulations including the dust component(in progress with B. Guiderdoni and E. Hivon)

Consequences

• This early dust can provide the seeds for the formation of molecules

• These molecules will then make the star formation efficient at z = 1-3, the major star producing event in the Universe.

• Planck will put strong constraints on this scenario (submillimetre capabilities of HFI).

• In theory, there is no difference between theory and practice. In practice, there is. (Chuck Reid)

Star formation history

Gispert et al. 2000, AA

Pierre Encrenaz

• Dark baryonic matter• Dark matter• Dark energy• Dark Pierre : his influence on French Astronomy

• String theory• Acoustic peaks in the CMB: the cosmic drum• Thanks for the practice of 16 strings and the 7 last

words (Haydn).