Cosmology with SCUBA-2

The UK National Astronomy Meeting (this year being held in conjunction with the German Astronomical Society) is underway this week in Manchester, UK.  The conference included a specialist session on SCUBA-2 results and it was especially pleasing to see SCUBA-2 data being presented in other sessions also,including one tied to a press release issued by the SCUBA-2 Cosmology Legacy Survey and the Royal Astronomical Society.

You can read the press release, as well as a report by the BBC – don’t forget to listen to the interview on that BBC page with Prof. James Dunlop from the University of Edinburgh, one of the leaders of the SCUBA-2 Cosmology Legacy Survey.

abell 1835, a lensing cluster

The subject of this post is Abell 1835, a galaxy cluster at a redshift of z=0.25 that is so massive that it acts as a gravitational lens to amplify the emission from objects at higher (i.e. more distant) redshifts along the line of sight. As well as amplifying the emission from faint and distant galaxies, another advantage of gravitational lenses is that they amplify light achromatically, that is, the amplification is equal at all wavelengths. Gravitational lensing allows us to study the properties of distant galaxies in far greater detail than would otherwise be possible; these rare lensing systems have thus allowed astronomers to push the boundaries of our exploration of the galaxy populations of the early Universe. This was used to good effect at the start of the century with SCUBA and led to the discovery a previously hidden population of submm galaxies by surveying for bright submillimetre radiation associated with known gravitational lenses.

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Revisiting SHADES

In mid-April, we obtained some data towards the Lockman Hole, a region of the sky located in the constellation Ursa Major whose line-of-sight is devoid of interstellar hydrogen. Consequently, this provides a clear window to the rest of the Universe beyond our Milky Way and the Lockman Hole has become a popular field to observe by cosmologists.

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Early extragalactic result – M51

M51 at 850 µm seen as the contour lines overlaid onto a 3-colour composite image of HST data.

The image above shows one of our first attempts at observing an object from outside our Galaxy and Solar System with SCUBA-2. It is a short 30 minute integration at 850 µm, which has been reduced by James Geach (Univ. McGill) for us. The underlying colour image is a HST composite and the contours are the SCUBA-2 data.

It is still too early to use these data to evaluate how we are doing with observing extragalactic sources. The observing mode was not optimum and the weather was average at best (CSO tau was ~ 0.1 for those interested!). Nevertheless, it is pleasing to see how we have easily detected the  nuclei of the two interacting galaxies, the fainter 850 µm emission that traces the dust lanes seen as dark in the inner regions of the spiral arms in the optical image (a larger version of the image is available; zoom in for a closer look), and that we are also sensitive to regions of hot star formation seen in the outer arms of the spiral galaxy.