The large-scale Structure and dynamics of the local universe

Abstract

This thesis investigates the dynamics of the local Universe with particular reference to discovering the source of the Local Group (LG) motion. A redshift survey of the Great Attractor (GA) region, thought responsible for a significant fraction of the LG motion, is presented. Over 3053 galaxies, located in both clusters and filaments, were targeted using the 2dF on the AAT. Velocity distributions and mass estimates for nine clusters are reported. Together with redshifts from the literature, this survey reveals the dominant feature in the core of the GA to be a large filament extending from Abell S0639 (l= 281º, b=+11º) towards a point at I ~ 5º b ~ -50º , encompassing the Cen-Crux, CIZA J1324.7-5736, Norma and Pavo II clusters. A new model of the local velocity field out to ՅՕՕh(^-1) Мрc is derived from the combined REFLEX, BCS and CIZA surveys: the RBC catalogue. This is the first all-sky, X-ray selected galaxy cluster sample. The reconstruction includes an intrinsic correction for the bias of clusters in tracing the total density field. The velocity fields from both this reconstruction and that of the PSCz survey are compared to the observed peculiar velocities of 98 local type la supernovae (SNIa). The best fits are respectively found for values of βRBC(= Ω(^0.6)m /(^b)RBC) = 0.39±0.20 and βι = 0.55±0.06. These results are found to be robust to culls of the SNIa sample by distance, host-galaxy extinction and the reference frame in which the comparison is carried out. As the PSCz preferentially samples late-type galaxies, the derived density field under- Samples the contributions from regions of greatest over density, precisely the regions traced by the RBC survey. When combined in the ratio 78% PSCz, 22% RBC these two complimentary reconstructions are a better fit to the ресuliar velocities of the same SNIa sample than either one alone. Compared to galaxy surveys, which only see contributions to the LG motion from structures within -60h(^-1) Мрc, previous cluster surveys have argued that sources at much greater distances (~150h(^-1) Mpc) influence local dynamics. However, the RBC reconstruction presented here shows similar contributions from the same depths as the PSCz, which is partly attributed to the intrinsic bias correction and inclusion of the Virgo cluster in the RBC. The extended GA region, defined as the volume enclosed by 250 < / <350º, 一45 < ь < 45º and 2000 <cz< 6000 km s (^-1) is found to be responsible for 65% of the LG motion, whilst the more distant (~ 145h(^-1) Mpc) SSC only accounts for 12%.