Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Two ground-based experiments have recently independently detected TeV γ-rays from the direction of the galactic centre. The observations made by the VERITAS and CANGAROO collaborations are unexpected, although not impossible to interpret in terms of astrophysical sources. Here we examine in detail whether the observed γ-rays may arise from the more exotic alternative of annihilations of dark matter particles clustered in the centre of the galaxy. ©2004 IOP Publishing Ltd.

Abstract:

The Oxford-Dartmouth Thirty Degree Survey (ODTS) is a deep, wide, multiband imaging survey designed to cover a total of 30 deg² in BV Ri′Z, with a subset of U- and K-band data, in four separate fields of 5-10 deg² centred at 00:18:24 +34:52, 09:09:45 +40:50, 13:40:00 +02:30 and 16:39:30 +45:24. Observations have been made using the Wide Field Camera on the 2.5-m Isaac Newton Telescope (INT) in La Palma to average limiting depths (5σ Vega, aperture magnitudes) of U = 24.8, B = 25.6, V = 25.0, R = 24.6 and i′ = 23.5, with observations taken in ideal conditions reaching the target depths of U = 25.3, B = 26.2, V = 25.7, R = 25.4 and i′ = 24.6. The INT Z-band data were found to be severely effected by fringing and, consequently, are now being obtained at the MDM observatory in Arizona. A complementary K-band survey has also been carried out at MDM, reaching an average depth of K5σ ≈ 18.5. At present, approximately 23 deg² of the ODTS have been observed, with 3.5 deg² of the K-band survey completed. This paper details the survey goals, field selection, observation strategy and data reduction procedure, focusing on the photometric calibration and catalogue construction. Preliminary photometric redshifts have been obtained for a subsample of the objects with R ≤ 23. These results are presented alongside a brief description of the photo-metric redshift determination technique used. The median redshift of the survey is estimated to be z ≈ 0.7 from a combination of the ODTS photometric redshifts and comparison with the redshift distributions of other surveys. Finally, galaxy number counts for the ODTS are presented which are found to be in excellent agreement with previous studies.