Mirrors Finished For James Webb Space Telescope

The deepest images of the universe include the Hubble Ultra-Deep Field (UDF) in the optical (Beckwith et al., 2003), which reaches AB = 29.0 mag in the I band, HST near-IR images of the UDF, which reach AB = 28.5 in the J and H bands (Bouwens et al., 2005a), and the Spitzer Great Observatories Origins Deep Survey (Dickinson, 2004), which reaches AB = 26.6 mag at 3.6 m. Galaxies are detected in these observations at 6

Or how about this:

Hierarchical Assembly: The dark matter mass function of bound objects at very high redshifts can be uniquely measured in two ways with JWST. First, the dynamics of groups of galaxies or sub-galactic fragments can be used to determine the typical masses of halos (Zaritsky and White, 1994).
These measurements require observations of emission lines in the rest-frame optical, such as [OII] 3727, [OIII] 5007, and H. These are very difficult to measure from the ground when redshifted into the near-IR.
Second, JWST will measure halo masses through the gravitational bending of light. Using this weak-lensing method, ground-based programs have measured the mass within 200?500 kpc of galaxies at redshifts of z 0.1 (McKay et al., 2002) and z 1 (Wilson et al., 2001). Using the superior resolution of HST, these measure- ments are likely to be extended into 30?50 kpc for galaxies at z 1 (e.g., Rhodes et al., 2004; Rhodes, 2004). While there are some hints of variable halo struc- tures for galaxies of different luminosity and total halo mass, the radial penetration of these surveys, and the ability to compare galaxies of different morphologies are
518 J. P. GARDNER ET AL.
limited by statistics. We expect that HST will establish the statistical mass functions for spiral and elliptical galaxies at z 1, but not much beyond that, because of its limited sensitivity and sampling at > 1.6 m.
JWST will extend the equivalent measurements of galaxies to z 2.5 and thus determine the development of the dark matter halos during the peak growth of galaxies and star formation. JWST will require near-IR imaging with high spatial resolution and sensitivity to achieve this greater depth. Background galaxies with a size comparable to the resolution of JWST will be measured at 20 .
The same near-IR sensitivity and resolution will also make JWST superior to those of ground-based facilities and HST for the study of dark matter structures on larger scales, e.g., 1?10 arcmin or 2?20 Mpc (co-moving) at z 3. These volumes measure the clustering of dark matter on cluster or even supercluster scales, and would extend the study of the mass function into the linear regime. The goal of these observations would be to verify the growth of structure between z 1000 (the CMB large-scale structure) and z 2.5, i.e., during the period that dark matter dominated the cosmological expansion of the universe prior to the beginning of dark energy dominance at z 1.

It's not all about the redshift, the paper also describes potentially useful observations in the IR-- planet formation, star formation, etc. And,of course, optical telescopes have a hard time resolving what's behind dust clouds-- ir telescopes can see beyond them

Source: http://rss.slashdot.org/~r/Slashdot/slashdotScience/~3/UU231zn_rn0/mirrors-finished-for-james-webb-space-telescope

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