From: "Jennifer C"
Date: Sun, 16 May 2004 18:14:32 -0700

Q Could u please tell me the earliest redshift interval at which galaxies and quasars are currently known to exist? Many thanks!

A Numerous examples are known of quasars/galaxies at redshift ~6, when the universe was less than ~1/7 its present size. The farthest example I could find easily in the literature occurs at redshift ~6.6 or so (paper at
http://www2.keck.hawaii.edu/news/Z_7/Z_7_Paper.pdf, press release at http://www2.keck.hawaii.edu/news/Z_7/z_7.html). This galaxy was discovered in February using the Hubble Space Telescope and the Keck Telescope.

It's very difficult to detect objects with redshifts greater than 6 with our current technology. Not only do the galaxies appear very dim because of their great distance, but because of redshifting their light is primarily in
the infrared. We don't have many great telescopes in this wavelength band, but there's hope that the next-generation James Webb Space Telescope can find many more distant galaxies.

There was a claim recently by the ISAAC/VLT group of a galaxy at z~10 (a galaxy called IR1916, which lies behind the galaxy cluster Abell 1835), which is much farther out than any other such claim. This corresponds to a time when the universe was less than a tenth of its present size, and the galaxy is believed to be 13.2 billion light years away. The VLT team uses gravitational lensing to look for very distant galaxies - the gravitational
field of a nearby galaxy cluster can bend the light coming from a distant source, and if the angles are right the distant source can appear magnified and brighter than normal. This lensing can let you find objects that would
normally be too dim and far away for our telescopes to see. This group believes that the object they see is a "proto-galaxy", about 10 times smaller than our Milky Way. At least one other group of astronomers does
not agree with the way the ISAAC group has analyzed their data, however.

The original paper announcing the redshift 10 galaxy is at http://www.arxiv.org/PS_cache/astro-ph/pdf/0403/0403025.pdf. The group's website (with press releases and descriptions) is http://obswww.unige.ch/sfr/.

Hope that helps!

Jeff Filippini
UC Berkeley Cosmology Group