Astronomical instrumentation

Abstract:

(Abridged) We have used the Rayner & Best (1989) smooth tests of goodness-of-fit to study the Gaussianity of the Very Small Array (VSA) data. Out of the 41 published VSA individual pointings dedicated to cosmological observations, 37 are found to be consistent with Gaussianity, whereas four pointings show deviations from Gaussianity. In two of them, these deviations can be explained as residual systematic effects of a few visibility points which, when corrected, have a negligible impact on the angular power spectrum. The non-Gaussianity found in the other two (adjacent) pointings seems to be associated to a local deviation of the power spectrum of these fields with respect to the common power spectrum of the complete data set, at angular scales of the third acoustic peak (l = 700-900). No evidence of residual systematics is found in this case, and unsubstracted point sources are not a plausible explanation either. If those visibilities are removed, a cosmological analysis based on this new VSA power spectrum alone shows no differences in the parameter constraints with respect to our published results, except for the physical baryon density, which decreases by 10 percent. Finally, the method has been also used to analyse the VSA observations in the Corona Borealis supercluster region (Genova-Santos et al. 2005), which show a strong decrement which cannot be explained as primordial CMB. Our method finds a clear deviation (99.82%) with respect to Gaussianity in the second-order moment of the distribution, and which can not be explained as systematic effects. A detailed study shows that the non-Gaussianity is produced in scales of l~500, and that this deviation is intrinsic to the data (in the sense that can not be explained in terms of a Gaussian field with a different power spectrum).

Abstract:

We present a deep photometric (B- and R-band) catalog and an associated spectroscopic redshift survey conducted in the vicinity of the Hubble Deep Field-South. The spectroscopy yields 53 extragalactic redshifts in the range 0 < z < 1.4, substantially increasing the body of spectroscopic work in this field to over 200 objects. The targets are selected from deep Anglo-Australian Telescope prime-focus images complete to R < 24, and the spectroscopy is 5 0% complete at R = 23. There is now strong evidence for a rich cluster at z ≃ 0.5 8 flanking the Wide Field Planetary Camera 2 field, which is consistent with a known absorber of the bright QSO in this field. We find that photometric redshifts of z < 1 galaxies in this field based on Hubble Space Telescope data are accurate to σ z/(1 + z) = 0.03 (albeit with small number statistics). The observations were carried out as a community service for Hubble Deep Field science in order to demonstrate the first use of the nod-and-shuffle technique with a classical multiobject spectrograph and to test the use of microslits for ultrahigh multiplex observations along with a new volume phase holographic grism and deep-depletion CCD. The reduction of this new type of data is also described. © 2006. The American Astronomical Society. All rights reserved.