Redshift Seven

June 29, 2011

I am very happy today to report a triumph for UKIDSS, for Dan Mortlock and Steve Warren, and for UKIRT  : the first quasar to break the redshift seven barrier. You can read the Mortlock et al Nature paper, the STFC story, the Gemini version, or the ESO version. And Telescoper has already splashed it too ! The science is best in the Gemini version, but the ESO has wonderfully gaudy animations….

When we were designing UKIDSS back in 1998-2001, SDSS was doing its thing and the redshift record climbed from 5ish to 6.3. The secret was finding i-band dropouts, as the famous forest cuts out nearly all light shortward of Lyman alpha. However this can’t work past z=6.4 as you get no visible light at all. Bring on the massive IR survey please… This was Steve Warren’s big push, along with the importance of the new Y-band, so we could tell the difference between high-z quasars and T-dwarfs. Finding these swines though is the classic needle in a haystack problem, with millions of fake candidates to weed out. Dan Mortlock has worked long hard and patiently, along with Steve Warren, Bram Venemans, Richard McMahon and others. Team UKIDSS were starting to get worried, as we were succesfully finding more 6ish quasars, but nothing past the magic 6.4… then suddenly bang – redshift 7.085.

Apart from breaking records, the new quasar is important in two ways. First, the Ly-alpha line is eaten away even redward of the peak, implying a small “near-zone” size, and so the best evidence so far for a significant neutral fraction near the quasar. Second, it has an estimated mass of two billion solar masses at just 770 million years after the Big Bang. It is generally thought that the very first stars, and so the first seed black holes, won’t be there until about z=25; then any such seed should not be able to grow by accretion to two billion solar masses until at least 900 million years…

Quasar near-zone

Artists impression of ionised bubble formed around quasar ULASJ1120+0641

Anyhoo. Although ESO and Gemini are getting lots of excellent PR, I think this is a triumph for UKIRT . Not dead yet, squire. In fact, how do we get more of these beasties, and push on to redshift 8 ? Survey the rest of the Northern Hemisphere, thats how. Another four years will do. (OK, VISTA helps too…).

Other thoughts. The Infra-red is cool. Big public surveys work. And for such massive surveys, properly processed and archived data is crucial. The whole thing would have been impossible without the selfless work of the teams at CASU and WFAU. Thank you guys.

Get your own data at the WSA ! DR9 coming your way soon.