A new most distant galaxy

When I wrote Measuring the Universe, the most distant galaxy that astronomers had ever observed lay at a redshift of z = 5.64. In the intervening years, the record for “most distant galaxy” has never been held by one object for long; astronomers keep peering further back in time and further out in space. The latest object to hold the record is MACS0647-JD, a tiny galaxy that lies at a redshift of 11 (give or take).

The galaxy’s discovery is described in a recent preprint (15 November 2012) entitled CLASH: Three Strongly Lensed Images of a Candidate z ~ 11 Galaxy. CLASH stands for Cluster Lensing And Supernova Survey with Hubble (yes, it’s yet another acronym): it’s an international group led by Marc Postman of STSI that uses the gravitational lensing effect of massive galaxy clusters to magnify distant galaxies that lie behind them. In the case of MACS0647-JD, light from this ancient galaxy set off on its way to us about 13.3 billion years ago. About 8 billion years after it set off on its journey, the light encountered a galaxy cluster called MACS J0647+7015. This cluster is so massive that it distorts the spacetime around it, causing light from MACS0647-JD to take multiple paths. The CLASH team were able to observe three different, magnified images of the galaxy; without the gravitational lens provided by nature it would have been extremely difficult to observe such a faint, distant object with current telescopes.

MACS0647-JD is so far away, in fact, that it might be a long time before for a telescope confirms the redshift based on spectroscopy. But the CLASH analysis looks robust: this tiny object, just 600 light years in diameter, is the current galactic distance record holder.

The current most distant galaxy

A composite image of MACS0647-JD taken by instruments on the Hubble Space Telescope. The inset shows a close-up of the galaxy.
(Credit: NASA, ESA, M. Postman & D. Coe (STScI), & CLASH Team.)