The Very Small Array

5.8 The Very Small Array

Although the CAT has already provided maps of CMB anisotropy on scales $∼$ 0.25° these are relatively poor as images due to the limited number of baseline lengths and pixels available. In fact, the CAT is a prototype for a considerably more advanced instrument, the Very Small Array (VSA). The objectives of the VSA are to obtain detailed maps of the CMB with a sensitivity approaching $5 μK$ and covering a range of angular scales from 10’ to 2°. An artists impression of the VSA is shown in Figure 16

Figure 16: Artist’s impression of the completed VSA array.

Using two interchangeable $T$ -shaped configurations of 10–15 horn elements, simulations have shown that it is possible to obtain maps of suitable sensitivity over the desired range of angular scales. The planned instrument would be sited at the Teide Observatory, Tenerife, at an altitude of 2400 m and would make observations between 28 and 38 GHz, to enable the Galactic component to be estimated and removed. The good accuracy available over a scale range that is well-matched to the positions of the first and secondary Doppler peaks in the power spectrum, should enable measurements of $Ω$ and $H0$ to be made to an accuracy of better than 10% after 12 months of observations. We believe that this will be refined somewhat by better array configuration design and the use of proper models and secondary peak information (all work in progress). In addition, simulations have shown that the proposed observing strategy will be quite sensitive to the non-Gaussian features expected on these angular scales if (e.g.) textures or monopoles are the seed perturbations for galaxy formation (Maisinger, Hobson, Lasenby & Turok [55 ]). The instrument is currently under construction at Cambridge and Jodrell Bank in the U.K., and is hoped it will be operational by the year 2000.