arXiv subjects
Publications and source records attributed to Will Sutherland.
We have extended the PSCz to cover 93% of the sky, the practical limit for any catalogue based on the Point Source Catalog. The galaxy identifications are complete, and the core of the Great Attractor is quantitatively mapped for the first time. We discuss the likely effect of the increased sky coverage on the IRAS dipole.
We present the results for the predicted density and peculiar velocity fields and the dipole from the PSCz survey of 15,000 IRAS galaxies over 84% of the sky. We find a significant component to the dipole arising between 6000 and 15,000 km/s, but no significant component from greater distances. The misalignment with the CMB is 20 degrees. The most remarkable feature of the PSCz model velocity field is a coherent large-scale flow along the baseline connecting Perseus-Pisces, the Local Supercluster, Great Attractor and the Shapley Concentration. We have measured the parameter beta using the amplitude of the dipole, bulk flow and point by point comparisons between the individual velocities of galaxies in the MarkIII and SFI datasets, and the large-scale clustering distortion in redshift space.All our results are consistent with beta = 0.6 +- 0.1.
We present the catalogue and redshift data for the PSCz survey of 15,000 IRAS galaxies over 84% of the sky. The uniformity, completeness and data quality are assessed, and guidelines and caveats for its use are given.
We perform a detailed comparison of the IRAS PSCz and 1.2-Jy spherical harmonic coefficients of the density and velocity fields in redshift space. The monopole terms predicted from the two surveys show some differences. The mismatch between the velocity monopoles arises from faint sources and disappears when extracting a PSCz subsample of galaxies with fluxes larger than 1.2 Jy. The analysis of PSCz dipole moments confirms the same inconsistencies found by Davis, Nusser and Willick (1996) between the IRAS 1.2-Jy gravity field and MARK III peculiar velocities. We conclude that shot-noise, which is greatly reduced in our PSCz gravity field, cannot be responsible for the observed mismatch.
There is abundant evidence that the mass of the Universe is dominated by dark matter of unknown form. The MACHO project is one of several teams searching for the dark matter around our Galaxy in the form of Massive Compact Halo Objects (MACHOs). If a compact object passes very close to the line of sight to a background star, the gravitational deflection of light causes an apparent brightening of the star, i.e. a gravitational `microlensing' event. Such events will be very rare, so millions of stars must be monitored for many years. We describe our search for microlensing using a very large CCD camera on the dedicated 1.27m telescope at Mt. Stromlo, Australia: currently some 14 events have been discovered towards the Large Magellanic Cloud. The lack of short-timescale events excludes planetary mass MACHOs as a major contributor to the dark matter, but the observed long events (durations 1--6 months) suggest that a major fraction may be in fairly massive objects $\sim 0.5 \Msun$. It is currently difficult but not impossible to explain these events by other lens populations; we discuss some prospects for clarifying the nature of the lenses.
We describe the construction of catalogues of galaxy clusters from the APM Galaxy survey using an automated algorithm based on Abell-like selection criteria. We investigate the effects of varying several parameters in our selection algorithm, including the magnitude range, and radius from the cluster centre used to estimate the cluster richnesses. We quantify the accuracy of the photometric distance estimates by comparing with measured redshifts, and we investigate the stability and completeness of the resulting catalogues. We find that the angular correlation functions for different cluster catalogues are in good agreement with one another, and are also consistent with the observed amplitude of the spatial correlation function of rich clusters.
We analyse the spatial clustering properties of a new catalogue of very rich galaxy clusters selected from the APM Galaxy Survey. These clusters are of comparable richness and space density to Abell Richness Class $\geq 1$ clusters, but selected using an objective algorithm from a catalogue demonstrably free of artificial inhomogeneities. Evaluation of the two-point correlation function $ξ_{cc}(r)$ for the full sample and for richer subsamples reveals that the correlation amplitude is consistent with that measured for lower richness APM clusters and X-ray selected clusters. We apply a maxmimum likelihood estimator to find the best fitting slope and amplitude of a power law fit to $ξ_{cc}(r)$, and to estimate the correlation length $r_{0}$ (the value of $r$ at which $ξ_{cc}(r)$ is equal to unity). For clusters with a mean space density of $1.6\times 10^{-6}\hmpccc$ (equivalent to the space density of Abell Richness $\geq 2$ clusters), we find $r_{0}=21.3^{+11.1}_{-9.3} \hmpc$ (95% confidence limits). This is consistent with the weak richness dependence of $ξ_{cc}(r)$ expected in Gaussian models of structure formation. In particular, the amplitude of $ξ_{cc}(r)$ at all richnesses matches that of $ξ_{cc}(r)$ for clusters selected in N-Body simulations of a low density Cold Dark Matter model.