Prof Gavin Dalton

Abstract:

In this paper we describe two coating and fabrication techniques we have developed applicable to astronomical instrumentation with particular emphasis on the FMOS instrument for the Subaru telescope.

Abstract:

The VISTA IR Camera has now completed its detailed design phase and is on schedule for delivery to ESO's Cerro Paranal Observatory in 2006. The camera consists of 16 Raytheon VIRGO 2048×2048 HgCdTe arrays in a sparse focal plane sampling a 1.65 degree field of view. A 1.4m diameter filter wheel provides slots for 7 distinct science filters, each comprising 16 individual filter panes. The camera also provides autoguiding and curvature sensing information for the VISTA telescope, and relies on tight tolerancing to meet the demanding requirements of the f/1 telescope design. The VISTA IR camera is unusual in that it contains no cold pupil-stop, but rather relies on a series of nested cold baffles to constrain the light reaching the focal plane to the science beam. In this paper we present a complete overview of the status of the final IR Camera design, its interaction with the VISTA telescope, and a summary of the predicted performance of the system.

Abstract:

FMOS is a near-IR OH-suppressed multi-fibre fed spectrograph for the Subaru telescope. The spectrograph will accept 200 optical fibres from the ECHIDNA positioner system at the 30arcmin Prime focus of the telescope. We will describe the recent activities here in the UK in progressing the instrument from its conceptual phase through detailed design and into manufacture. A variety of technical areas will be described including: the opto-mechanical system design and construction, development of the HAWAH-II detector control system, the thermal system design & control and OH suppression techniques.

Abstract:

The Two-degree Field Galaxy Redshift Survey (2dFGRS) Percolation-Inferred Galaxy Group (2PIGG) catalogue of ∼29 000 objects is used to study the luminous content of galaxy systems of various sizes. Mock galaxy catalogues constructed from cosmological simulations are used to gauge the accuracy with which intrinsic group properties can be recovered. It is found that a Schechter function is a reasonable fit to the galaxy luminosity functions in groups of different mass in the real data, and that the characteristic luminosity L * is slightly larger for more massive groups. However, the mock data show that the shape of the recovered luminosity function is expected to differ from the true shape, and this must be allowed for when interpreting the data. Luminosity function results are presented in both the bJ and rF wavebands. The variation of the halo mass-to-light ratio, T, with group size is studied in both of these wavebands. A robust trend of increasing T with increasing group luminosity is found in the 2PIGG data. Going from groups with b] luminosities equal to 10¹⁰ h^-2 L ⊙ to those 100 times more luminous, the typical b J-band mass-to-light ratio increases by a factor of 5, whereas the rF-band mass-to-light ratio grows by a factor of 3.5. These trends agree well with the predictions of the simulations which also predict a minimum in the mass-to-light ratio on a scale roughly corresponding to the Local Group. The data indicate that if such a minimum exists, then it must occur at L ≲ 10¹⁰ h^-2 L⊙, below the range accurately probed by the 2PIGG catalogue. According to the mock data, the bJ mass-to-light ratios of the largest groups are expected to be approximately 1.1 times the global value. Assuming that this correction applies to the real data, the mean bJ luminosity density of the Universe yields an estimate of Ωm = 0.26 ± 0.03 (statistical error only). Various possible sources of systematic error are considered, with the conclusion that these could affect the estimate of Ωm by a few tens of per cent.