December 13, 2012
Hubble Census Finds New Galaxies Near Cosmic Dawn
Lee Rannals for redOrbit.com - Your Universe Online
Astronomers have discovered seven primitive galaxies that formed more than 13 billion years ago, during the Universe's infancy.The find includes a candidate galaxy that could hold the record for the most distant galaxy ever found.
Scientists made the new discoveries using the Hubble Space Telescope's Hubble Ultra Deep Field project, which aims to improve our understanding of the early Universe.
Astronomers are looking back at these galaxies when they appeared 600 million years after the Big Bang.
The new data allowed the team to uncover six previously-unknown galaxies, and rule out tentative identifications of distant galaxies made by other scientists.
The observations are the first statistically robust census of galaxies at such an early time in cosmic history, showing that the number of galaxies steadily increased with time.
The team confirmed one previously-claimed candidate for extreme redshift galaxy, UDFj-39546284. Astronomers claimed this to be the most distant galaxy known. However, the improved and extended dataset allowed astronomers to find that the object lies at an even greater distance than previously thought.
“Our study has taken the subject forward in two ways,” said Richard Ellis, from Caltech and co-leader of the survey. “First, we have used Hubble to make longer exposures than previously. The added depth is essential to reliably probe the early period of cosmic history. Second, we have used Hubble´s available color filters very effectively to measure galaxy distances more precisely.”
When studying galaxies in the Universe's infancy, scientists have to work with the Hubble's limits. They must grapple with sometimes ambiguous data.
The team had to take additional data through filters that have already been used to take deep images of the Hubble Ultra Deep Field. The team also added new imaging through previously unexploited filters.
“We added an additional filter, and undertook much deeper exposures in some filters than in earlier work in order to convincingly reject the possibility that some of our galaxies might be foreground objects,” said team member James Dunlop from the University of Edinburgh.
The observations were made over a period of six weeks during August and September 2012, and the first results are now appearing in a series of scientific papers.
The goal of the Hubble project was to determine how rapidly the number of galaxies increased over time in the early Universe.
“This discovery of a significant population of galaxies at redshifts greater than 8, coupled with our new analysis of the number and properties of galaxies at redshift 7 and 8, support the idea that galaxies assembled progressively over time,” said project co-leader Ross McLure, also from the University of Edinburgh.