Deep 850um (top-left) and 450um (bottom-left) maps of the rich cluster A370 (z=0.37) taken with the SCUBA bolometer array on the 15-m JCMT, Hawaii. These are the first deep sub-millimeter maps of the distant Universe ever taken and they show a number of sub-mm sources detected at 850um. These objects are seen in the sub-mm because the dust within them is reprocessing UV and optical star-light and emitting large quantities of radiation in the sub-mm. Only one of these 850um sources (the brightest) is seen at 450um and the constraints this provides on the redshifts of the sources indicates that the majority of these objects are likely to lie at z>>1. If this is the case then these represent very luminous and strongly star-forming galaxies (`proto-galaxies'?). Optical surveys of the distant Universe have failed to uncover this population, probably due to the high optical obscuration caused by the dust. The high surface density of the sub-mm sources indicates that the population being missed by the optical surveys could account for over half the star-formation in the distant Universe. These data were acquired in collaboration with Rob Ivison and Andrew Blain.

The images on the right are 850um and 450um maps of the compact cluster lens Cl2244-02 (z=0.33). We detect two faint sources at 850um in this field, again they are weak or undetected at 450um indicating that they probably lie at high redshift. All the maps are roughly 180 arcsec in diameter and the major tick marks show 10 arcsec.

  • New images for the press release. These show the 850um SCUBA map of A370 (right) and a true-color image of the same field (left) constructed from BRI images. Links to the images in different formats are given here: Optical JPEG, Optical TIFF, SCUBA JPEG, SCUBA TIFF.

    CAPTION:These two images show different views of the same region of sky containing the gravitational cluster-lens Abell 370. On the left we have a true colour `optical' image made up of blue, red and near-infrared images taken with the 3.6-m Canada France Hawaii Telescope by Dr Jean-Paul Kneib of Toulouse Observatory. The optical image shows a giant gravitational arc seen through the centre of the cluster of galaxies, this is a image of a background galaxy distorted and magnified by the foreground cluster lens. A number of other distorted images of visible across the frame - as well as many of the galaxies actually within the cluster which appear yellow. There are obviously are a large number of very faint galaxies visible in this image, but it is impossible to tell which are the distant, young galaxies which are crucial for studying galaxy formation and evolution. However, on the right is the submillimetre SCUBA map of the same field, although this detects only a few objects these are all likely to be the dusty, young galaxies which are need to test models of galaxy formation. Thus SCUBA's submillimetre observations are critical for understanding the evolution of galaxies.

    The SCUBA 850um map of the cluster A1835 overlayed on a composite UBI ground-based image to show the optical counterparts to two of the bright SCUBA sources (the z=2.56 starburst galaxy on the left of the image and the bright central cluster galaxy at z=0.25 in the middle of the field). The brightest SCUBA source in this field (on the right) has no bright optical counterpart and is likely to be a highly obscured galaxy at high redshifts.


    Two objects selected from a CCD imaging survey of 0.25 sq. degrees of sky in UBI. These two objects have stellar profiles and relatively blue (B-I) colors, what sets them apart from other objects in the fields is their extremely red (U-B) colors considering their (B-I). The two objects have: I=18.4, (B-I)=2.5 and (U-B)>4.7; I=19.8, (B-I)=2.1 and (U-B)>3.3. Where the (U-B) values are 1 sigma upper limits given no detection (U>25-25.5). The typical errors on the B/I photometry are 0.05 mag. The image below shows the IBU images (from left to right) for each object. Their total absence from the U image indicates that the Lyman break in these objects lies redward of this passband. Combined with their relatively blue (B-I) colors this argues for them lying at z>3, and given their luminosities and compact nature these are likely to be QSOs. The two images at the bottom show `true' color representations of the UBI exposures of A2261 and A1758, coded as U=blue, B=green and I=red. The yellow star-like object in the center of each frame is the QSO. Update: Spectroscopy with the WHT by Alastair Edge and Richard Ellis shows these two objects to be at z=3.85 and z=3.72, the z=3.85 having two damped Lyman-alpha features and a Lyman limit systems.


    Last Modified: April 25th, 1997. [Netscape 2.0]