Herschel-ATLAS New Data Release

The Herschel-ATLAS Data Release 1 (DR1) is one of the largest public release of data from the Herschel Observatory so far and will be a powerful data-set for studies of galaxy evolution. It covers the three equatorial fields surveyed by the GAMA spectroscopic survey. The three fields are 161 sq deg combined, and are located around 09h, 12h and 14h in RA.

The catalogue, described in Valiante et al. 2016, covers all three regions and includes 120230 sources in 5 photometric bands - 100, 160, 250, 350, 500 micron. It also provides a robust optical identification from the SDSS DR7/8 catalogue and spectroscopic redshifts from GAMA and SDSS for 44819 sources (Bourne et al. 2016).

The data release includes several maps and additional files described in Valiante et al. 2016.

The size of the survey means that the survey contains both large numbers of nearby galaxies like our own, which can be detected with conventional optical telescopes, and very distant galaxies whose light has taken billions of years to reach us. The most distant galaxies in the survey are being seen as they were 12 billion years ago, only shortly after the Big Bang. They are so dusty that they are virtually impossible to detect with standard telescopes and are often gravitationally magnified by intervening galaxies. These early systems are the distant ancestors of galaxies like our own.

Dr Elisabetta Valiante of Cardiff University, lead author of one of the papers describing the catalogues, says: “The exciting thing about our survey is that it encompasses almost all of cosmic history, from the violent star-forming systems full of dust and gas in the early universe that are essentially galaxies in the process of formation, to the much more subdued systems we see around us today.”

The huge size of the survey has meant that, for the first time, it has also been possible to study the changes that have occurred in galaxies comparatively recently in cosmic history. The team has shown that even only one billion years in the past, a small fraction of the age of the universe, galaxies were forming stars faster and contained more dust than galaxies today.
 
According to Dr Nathan Bourne of the University of Edinburgh, and the lead author of the other paper describing the catalogues: “We were surprised to find that we didn’t need to look far in the past to see signs of galaxy evolution. Our results show that the reason for this evolution is that galaxies used to contain more dust and gas in the past, and the universe is gradually becoming cleaner as the dust is used up.”

The catalogues and maps of the hidden universe are a triumph for the Herschel team. They will be vital tools for astronomers trying to explore the history of galaxies and the wider cosmos.

Dr Loretta Dunne, another Cardiff University scientist, and co-leader of the project adds: “Before Herschel we only knew of a few hundred such dusty sources in the distant universe and we could only effectively 'see' them in black and white. Herschel, with its five filters, has given us the equivalent of technicolour, and the colours of the galaxies tell us about their distances and temperatures. So now we have half a million galaxies we can use to map out the hidden star formation in the universe.”

As emphasized by Göran Pilbratt, the Herschel Project Scientist, ‘Although Herschel made its last observation in 2013, current and future generations of astronomers will find the H-ATLAS maps and catalogues essential for finding their way around the hidden universe.’