In this thesis we investigate the clustering and evolutionary properties of massive galaxies. We present new measurements of galaxy clustering over a range of redshifts using data from the 2SLAQ Survey and the AAOmega LRG Pilot Survey. The clustering properties of Luminous Red Galaxies (LRGs) are measured using nearly 9 000 2SLAQ LRGs at a mean redshift of z = 0.55. We find that the real-space 2-point correlation function is well described by a single power-law of the form ع(r) = (r/ro)(^- ٦), where ٦ = 1.72 ± 0.06 and the correlation length ro = 7.45 ± 0.35 h (^-1) Мрc. Then we study the redshift-space distortions that are present in the clustering signal. From these dynamical and geometric distortions, we derive a value of Ω(_m) = 0.30 ± 0.15 and ß{z = 0.55) = 0.45 ± 0.05, where Ω(_m) is the present day matter density parameter and β = Ω(_m) /b where b is the linear bias parameter. We find for 2SLAQ LRGs, b(z = 0.55) = 1.66 ± 0.35. If one then assumes a "high-peaks" bias model, this value of b is consistent with the measured clustering strengths for low-redshift, massive early-type galaxies, under the assumption that gravitational growth leaves the comoving space density of early-types independent of redshift. We then use the new AAOmega instrument to perform a study of redshift z ~ 0.7 LRGs selected using riz-band photometry. We find a redshift-space correlation length of So = 9.9 ± 0.5 h-l Мрc and show that using LRGs as tracers would be a very competitive strategy for baryon acoustic oscillation studies in future galaxy redshift surveys. We also confirm that this population again has a clustering strength consistent with the above "high-peaks" bias model. Finally, we use data from the Spitzer and Hubble Space Telescopes taken in the COSMOS field and find tentative evidence for dust emission possibly coming from obscured star formation. We also show that z ~ 0.7 LRGs are predominantly early-type galaxies.

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%.

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This thesis presents optical CCD imaging taken as part of the follow-up programme to the Massive Cluster Survey, a ROSAT All-Sky Survey based cluster survey aiming to discover X-ray luminous galaxy clusters at redshifts above 0.3. A data-reduction pipeline is developed to process the V, R and I band imaging of 111 clusters observed with the University of Hawaii 2.2 metre telescope and 57 with the ESQ NTT. The galaxian population is examined and all clusters but one contain enough galaxies to account for the X-ray flux. The cluster red-sequence is used to constrain the star-formation epoch to high {z > 1.7) redshift and as a basis for photometric redshifts. The symmetry properties of the clusters are examined to probe merger activity, the cluster selection exhibiting no bias towards, or against, merging clusters. The BCG population is examined. The degree to which the BCG dominates the cluster galaxy population displays no trend with either redshift or cluster X-ray luminosity, indicative of considerable previous as well as ongoing evolution. A quarter of the BCG population show bluer colours than would be expected for an elliptical galaxy at the appropriate redshift, some with known line emission, proving that BCGs are not purely passively evolving galaxies. Multi-object spectroscopy of two clusters is used to confirm these as being massive. Colour-magnitude diagrams of spectroscopically selected galaxies are used to determine that the major source of error in the photometry to is the flux limit of the imaging not the techniques applied. The Veron-Cetty Veron AGN catalogue is cross-correlated with the Abell catalogue to reveal a sample of AGN in clusters which are found to be distributed within clusters as ordinary galaxies, making contamination to the observed X-ray flux a possibility. A search for gravitationally lensed galaxies reveals such objects in 23% of the clusters imaged.

This thesis explores the role of active galactic nuclei (AGN) in the heating of the intracluster medium (ICM). In the centre of many clusters the radiative cooling tune of the ICM is much shorter than the Hubble time. Unless cooling is balanced by some form of heating, gas will flow into the cluster centre at rates up to ~ 1000 M© yr(^-1). Recent Chandra and XMM-Newton X-ray observations present almost no evidence that this is happening incluster cores. Moreover, they show that the ICM has a rather complex structure. Some of the features in the X-ray images can be explained as the interaction of the central AGN with the ICM. The most prominent feature are bubbles of hot and underdense gas inflated by jets coming from massive black holes residing in the centre of giant elliptical galaxies. These bubbles are thought to rise buoyantly through the ICM and heat the gas by depositing their energy. I start by introducing the cooling-flow problem and by summarising the current understanding of the ICM heating processes. I then introduce the adaptive mesh refinement (AMR) code FLASH that has been used for the simulations in this thesis and the development of new routines and modules. A model of AGN heating is then applied to model clusters to investigate three issues: (1) the quenching of the cooling-flow by injection of bubbles of energy; (2) the determination of the AGN duty cycle by using measurements of sound wave positions; (3) the presence of a mass threshold below which the heating process is no longer effective. I show that cooling can be effectively balanced by AGN heating in a cluster of mass 3 x lO(^14) Mo. Then, I argue that by using measurements of sound wave positions it is possible to determine the duty cycle of the AGN with good accuracy. Finally, I show that there is a threshold mass for which the heating process is ineffective. In the light of this, I discuss the importance of the process in shaping the luminosity function of galaxies. I also apply the heating model to a cluster that has formed in a cosmological environment and discuss how to improve the code performance.

In this thesis we are interested in the properties of low redshift galaxies. In the first part, we look at the large-scale structure of the Sloan Digital Sky Survey galaxies using photometric redshifts. In the second part, we bring new insight into physical properties of galaxies, in particular into their dust content, and show how they are related to their near-infrared colours.

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The magnetic fields that thread extragalactic radio jets play an important role in the emission properties and evolution of these objects; knowledge of the structure and evolution of these magnetic fields is therefore important in forming a better understanding of jets by imposing constraints on theoretical models and simulations. This thesis presents a method to infer the geometry of the magnetic fields that thread jets by comparing the transverse (across the jet) emission properties of jets with predictions from models. Such comparisons are possible thanks to the high resolution radio images of jets produced using the technique of VLBI polarimetry, which allows forjets to be sufficiently resolved across their length. The radio images presented in this work reveal several features in the transverse structure of jets: i) the total and polarized intensity can be asymmetrically distributed across the jet, ii) the total and polarized intensity maxima can be significantly displaced with respect to each other, iii) total and polarized intensity may be edge brightened and iv) the apparent magnetic field may flip by an angle of 90° across the jet. All four features can be successfully explained by assuming that jets are threaded by magnetic fields of helical geometry. Models already proposed in the literature (examined by Laing 1981) are tested against observations and enhanced accordingly in order to account for any discrepancies with observations. These enhancements include the addition of a tangled magnetic field component and radial compression at the outer sheath of a jet. Comparisons with observations reveal that a helical magnetic field geometry of constant pitch angle combined with a tangled magnetic field component (to adjust the fractional polarization) can successfully predict the structure of the inner jet but fail at the edges where the predicted fractional polarization is lower than that observed; the radial compression is introduced in order to account for this discrepancy but despite this having the desired effect, predicted fractional polarization still falls short of the observed values. Comparisons with other geometries discussed by Laing (Chan-Henricksen, hollow jet) produced unsatisfactory results. One of the predictions of the helical magnetic field model is that the projected magnetic field can have one of four different behaviours, two of which are commonly observed (magnetic field across the jet being either parallel or perpendicular to the jet ridge line) and two less commonly (magnetic field across the jet abruptly changing from parallel to perpendicular and magnetic field being parallel at the edges and perpendicular at the middle). The two common behaviours have been associated with quasars (parallel field) and BL Lac objects (perpendicular field) (Cawthorne et al. 1993a, 1993b). A simple statistical model that predicts the likelihood of observation of these behaviours has been developed and is presented in this thesis. The results from the model show that the all parallel magnetic field behaviour (quasar type) is the most common while perpendicular magnetic fields can account for a small fraction (- 10 percent) of the observations. The model also suggests that the two uncommon behaviours should be more likely to be observed in high flux sources.