Seven surveys to serve up surprises
BY KULVINDER SINGH CHADHA
ASTRONOMY NOW

Posted: October 14, 2008

The Legacy Survey, an international study being undertaken with the James Clerk Maxwell Telescope (JCMT) in Hawaii, is an ambitious project composed of seven separate surveys that aim to understand the entire Universe, right down to the smallest planetary system.

The Legacy Survey is showing great promise and is already throwing up some surprises. Professor Derek Ward-Thompson of Cardiff University says, “Images from the HARP instrument [Heterodyne Array Receiver Programme] allow us to see a three-dimensional picture of star birth in molecular clouds. It shows just what a violent process star birth is. In fact it’s almost as violent as a star's death.” And adding to that, doctoral student Robert Simpson says, “The images produced by HARP have smashed my old notions of the beautiful and serene nebula. Images such as these reveal the violence and energy flowing inside.” The instrument is producing entire maps in hours — something that previously would have taken weeks to do.

The ambitious James Clerk Maxwell Telescope Legacy Survey is set to revolutionise astronomy. Image: Joint Astronomy Centre/James Clerk Maxwell Telescope.

The teams working on the surveys come from the UK, Canada and the Netherlands. Key to the success of this project are two brand-new instruments. One is the HARPS, which is a superconductive detector. In effect, it turns JCMT into a three-dimensional imaging device. The other instrument is the SCUBA-2 (Submillimetre Common-User Bolometer Array), which is a highly sensitive device that sees radiation from the coldest dust in space. Both of these instruments work in submillimetre wavelengths (between far-infrared and microwaves), which is the most unexplored electromagnetic region in astronomy.

The main components of the Legacy Survey are: the SCUBA-2 All Sky Survey (SASSy); the SCUBA-2 Cosmology Legacy Survey (CLS); the Nearby Galaxy Legacy Survey (NGS); the JCMT Galactic Plane Survey (JPS); the Gould Belt Survey (GBS); the Spectral Legacy Survey (SLS); and the Debris Disk Survey (DDS). Of these seven projects, NGS, GBS and SLS are up and running already. The other surveys will follow soon.

NGS, led by Professor Christine Wilson of McMaster University, Canada, Dr Frank Israel of Leiden University, Netherlands, and Dr Stephen Serjeant of the Open University (UK) aims to produce the first detailed submillimetre-wavelength map of galaxies within 82 million light years of the Milky Way. In fact NGS has hit the ground running, as Wilson says, “It has been very exciting over the last year to go from verifying the performance of HARP on the JCMT to completing over 80 percent of our survey. We have been kept very busy processing the flood of data that is being produced, but the reward has been seeing all these beautiful images of nearby galaxies appearing one by one.”

Wilson points out that this would not have been possible without HARP and the accompanying data processing in the form of ACSIS (Auto-Correlation Spectrometer and Imaging System). “We are using this new data from the NGS to map out how the dense gas, which is the fuel for forming new stars, is distributed in galaxies with different masses and environments. One of our exciting results is to be able to map for the first time how efficiently gas is being turned into stars, from one region of a galaxy to another.”

The three panels from the Spectral Legacy Survey show the colour scale and contours of the emission from three different molecules (sulphur monoxide, formaldehyde and a hydrocarbon chain (C2H)) towards the Orion Arm of the Milky Way. Asterisks mark the same sky position in each image. Image: Joint Astronomy Centre/James Clerk Maxwell Telescope.

And the surprises continue. GBS, a survey to plot star formation within 1,630 light years of our Solar System (led by Dr Jennifer Hatchell of the University of Exeter — amongst others) is giving the astronomers the highest-quality maps of proto-stellar gas clouds ever produced (the Gould Belt is a partial ring of stars 3,000 light years across, of which our Sun is a member). “Now we can see just how much the gas clouds are being moved about by the newly-forming stars inside them,” Hatchell says. Dr Michiel Hogerheijde of the Leiden Observatory in the Netherlands adds: “We knew about the outflows that are shooting off from the newly-formed stars and we can see them much better now. But they only contain a small fraction of the gas. What is really exciting is that with these rare types of molecules we can now also see the subtle effects that the outflows may have on the motion of the bulk of the gas, and on its ability to form more stars in the future.”

The third survey that is currently running, SLS, will fill in the gaps in the GBS data. SLS will obtain a ‘chemical inventory’ from various star-forming regions selected for their diversity. This will be especially important when looking at the behaviour of rare molecules.

To sum up the excitement over the prospects, shared by all the partners, JCMT Director Professor Gary Davis says, “This is the culmination of a process in which astronomers in the UK, Canada and the Netherlands came together to define a unified and comprehensive survey of the submillimetre sky. This has never been done before because the revolutionary instruments required to do it have not, until now, been available. The survey programme is of the highest scientific calibre and will have far-reaching effects on all areas of astrophysics. The spectacular results so far are just a tantalising hint of what is yet to come."

For more information about the JCMT and the Legacy Survey, go to: www.jach.hawaii.edu/JCMT/surveys/