A small glimpse of one region, a tenth of the full area of the Herschel ATLAS images. Everything in this image, apart from the picture of the Moon, which has just been placed there to show the area of sky covered by the survey and the small square that shows the area covered by the Hubble Deep Field, consists of far-infrared emission from cosmic dust. The faint wisps are far-infrared emission from dust grains in the Milky Way but everything else in the image is a dusty galaxy. There are approximately 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 ten 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. Credit: The Herschel ATLAS team and the European Space Agency
Astronomers have released a catalog of the hidden universe, which reveals the unseen sources of energy found over the last 12 billion years of cosmic history. Professor Gomez of Cardiff University presented this catalogue of the Universe’s hidden energy sources, made with the ESA Herschel Space Observatory, at the National Astronomy Meeting in Nottingham.
About half of the light emitted by stars and galaxies is absorbed by interstellar grains, tiny solid particles that are found everywhere in the space between the stars. The missing 50% has been a huge obstacle for astronomers trying to understand the births and lives of galaxies. When Herschel Space Observatory launched in 2009 it meant that, for the first time, it was possible to track down this hidden energy. The missing light is re-emitted by the dust grains into far-infrared radiation, detected by the Herschel telescope. For the last 7 years, an international team of over 100 astronomers has been analysing the images from the largest Herschel survey, named the Herschel Astrophysical Terahertz Large Area Survey (the Herschel ATLAS). Today sees the release of their first catalogues of the hidden universe.
The Herschel ATLAS discovered about half a million far-infrared sources. 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 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 for the first time, it has also been possible to study the changes that have occurred in galaxies comparatively recently. The team has shown that even only 1 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 describing the catalogues: “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 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.” https://www.ras.org.uk/news-and-press/2878-space-team-discovers-universe-is-self-cleaning
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