An international team of astronomers released a gazetteer of the hidden universe that reveals all unseen sources of energy that have been found over the last 12 billion years of cosmic history. Professor Haley Gomez from Cardiff University presented a complete catalogue of the Universe’s hidden energy sources which were made with the ESA Herschel Space Observatory at the National Astronomy Meeting in Nottingham.

Around half of the light emitted by stars and galaxies is absorbed by interstellar grains which are tiny particles that are located everywhere in the space between stars. The missing 50 percent has been a huge obstacle for astronomers who are trying to understand the births and lives of such galaxies.

When the European Space Agency (or ESA) Hershel Space Observatory launched in 2009 it became possible for the first time for hidden energy to be traced. The missing light is re-emitted by the dust grains into far-infrared radiation, detected by the Herschel telescope. For the past 7 years, an international team of more than 100 astronomers has been analyzing the images from the largest Herschel survey. This has been their first release of the first catalogues of the hidden universe.

A small peek of one region, only a tenth of the full area of the Herschel ATLAS images. Everything in this picture, aside from the picture of the Moon, which has just been fixed to show the area of sky covered by the survey and the small square that shows the area covered by the Hubble Deep Field, subsists of far-infrared emission from cosmic dust. The faint wisps are far-infrared emission from dust grains in the Milky Way, everything else in the image is a dusty galaxy. There are roughly 6000 dusty galaxies detected in this image, while the entire survey contains roughly half a million dusty galaxies, from galaxies similar to our own, to violently star-forming and very dusty galaxies that are being seen as they were over 10 billion years ago. This image also shows how the field of hidden astronomy has evolved. The Hubble Deep Field was the first area surveyed by a dust sensitive camera called SCUBA almost 20 years ago. Five galaxies were found and the observations took 50 hrs, meaning it took 10 hours observing time to detect a galaxy. The Herschel-ATLAS maps released today cover an area 100,000 times larger and it took Herschel only 5 seconds on average to detect a galaxy in these images. Image Credit: The Herschel ATLAS team and the European Space Agency

The Herschel ATLAS uncovered around a half a million far-infrared sources. The survey size means that the survey contains both large numbers of nearby galaxies like our own and extremely 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 around 12 billion years ago, just after the Big Bang. They are so dusty that they are just about impossible to detect with standard telescopes and are many times gravitationally magnified by intervening galaxies. These early systems are the distant ancestors of galaxies very similar to our own.

Dr. Elisabetta Valiante from Cardiff University, lead author of one of the papers 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 very large 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 been able to show that even only one billion years ago, a small fraction of the age of the universe, galaxies were forming stars faster and contained more dust than galaxies of today.

Lead author of one of the papers, Dr. Nathan from the University of Edinburgh says 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 created by the Herschel team will be a vital tool for astronomers who are looking to further explore the history of galaxies and the wider cosmos. Dr. Loretta Dunne, a co-leader of the project form Cardiff University says that before Herschel we only knew 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 Technicolor and the colors of the galaxies tell us about their distances and temperatures. Now we have a half a million galaxies we can use to map out the hidden star formation in the universe.

Professor Seb Oliver who helps to lead the Herschel Extragalactic Project (HELP) says it is fantastic to see these high quality data products emerge from H-ATLAS. He has no doubt that astronomers will be using these for decades to come, if not longer. Goran Pilbratt, a Herschel Project scientist adds that although Herschel made its last observation in 2013, current and future generations of astronomers will find that H-ATLAS maps and catalogues essential for finding their way around the hidden universe.