In the Dark

Once again I’ve spent all day engaged in the enjoyable but exhausting task of interview for new faculty positions, which means that I haven’t really got time for a proper blog today. What I can do, however, is shamelessly rip off a nice press release produced by the good folks here at the University of Sussex about a discovery that has been attracting a lot of press coverage since it was published last week in Nature; the paper is also available on the arXiv. If you’ve followed this blog for a while you will know than when I was at Cardiff I got interested in a large project called the Herschel Atlas survey, which is a large area galaxy survey carried out using the Herschel Space Observatory. This result is not from Herschel ATLAS but from a complementary deeper survey called Hermes, also performed using the Herschel Space Observatory and it is of a very distant and very bright starburst galaxy (a type of galaxy which, as its name suggests, in which stars are forming at a much higher rate than a “normal” galaxy).

Incidentally, although Herschel is now extremely short of the Helium it needs to keep itself cool, it is still making observations running on empty, as it were.

Anyway, that’s all I’ve got time to write. The rest is just copied from the press release I mentioned…

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University of Sussex astronomers using the Herschel Space Observatory are part of an international team that has discovered a distant star-forming galaxy that challenges the current theories of galaxy evolution.

Seen when the Universe was less than a billion years old (880 million years) the galaxy, known only as “HFLS3”, is forming stars at a much faster rate than should be possible according to existing predictions. In the infant Universe, galaxies should have been forming stars at a much slower rate than is observed in HFLS3.

HFLS3 is so distant that the light we see from it has taken 13 billion years to get to Earth.

The Herschel observatory1 has been surveying the distant cosmos and finding hundreds of thousands of distant galaxies. Images produced by Herschel show how fast these distant galaxies are forming stars.

By determining the ages of the galaxies, astronomers have been building up a cosmic timeline of star formation, searching for when the first massive galaxies started churning out stars.

University of Sussex PhD student Peter Hurley, Dr Isaac Roseboom, Dr Anthony Smith, Dr Lingyu Wang and Professor Seb Oliver, who leads the HerMES2 survey that found the galaxy, analysed data from Herschel and built the HFLS3 galaxy as a computer model to discover what conditions are like in the galaxy.

Peter says: “The stars being born in HFLS3 heat up the surrounding material within the galaxy. This material contains gas molecules such as carbon monoxide and water, which emit their own unique signatures when heated. By comparing the telescope observations with models, we can gain a better understanding of the conditions within this extreme galaxy.”

The galaxy “HFLS3” was first seen as a small red dot in the Herschel images, and its colour is what first intrigued the team because red galaxies might be very distant.

The galaxy HFLS3 as revealed by Herschel and further ground-based telescope observations. Images: ESA/Herschel/HerMES/IRAM/GTC/W.M. Keck Observatory

Further investigations using optical and near-infrared telescopes the Gran Telescopio Canarias in the Canary Islands and the Keck Telescope in Hawaii helped to rule out any other effects that might cause the HFLS3 galaxy to look so bright.

It was observations with radio and millimetre-wave telescopes, such as the Plateau de Bure Interferometer in the French Alps, which determined that this tiny galaxy, only around one twentieth the size of our Milky Way, is seen at such an immense distance. These additional observations also showed that HFLS3 is incredibly rich in carbon, nitrogen and oxygen, forming compounds such as carbon monoxide, water and ammonia. These compounds reveal the physical processes at work in this distant galaxy.

Combined with the Herschel observations, these measurements allow the astronomers to deduce that this tiny star factory is producing stars around two thousand times faster than our own Milky Way, making it a type of galaxy known as a “starburst”. Environments like this do not exist on galaxy-wide scales in the Universe today.

Professor Oliver says: “We’ve shown that Herschel data can find these extreme examples. “The next step is to sift through the Herschel data more carefully, and try to deduce just how common such galaxies were in the early Universe. I am also very pleased that a Sussex PhD student has been able to make an important contribution to this work.”

Jamie Bock (Caltech, USA), who co-leads the HerMES survey with Professor Oliver, says: “This galaxy is just one spectacular example, but it’s telling us that early star formation like this is possible,” explains Jamie Bock, Caltech, and one of the leaders.

Dominik Riechers (Cornell University, USA), who led the HFLS3 study, says: “Looking for the first examples of these massive star factories is like searching for a needle in a haystack. We were hoping to find a galaxy at such vast distances, but we could not expect that they even existed that early on in the Universe.”

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