In this thesis I investigate galaxy evolution at high redshifts and in a dense galaxy-cluster.

I cross-correlate the WMAP third year data with the АСО, АРМ and 2MASS galaxy and cluster catalogues, confirming the presence of the SZ effect in the WMAP 3rd year data around АСО, АРМ and 2MASS clusters, showing an increase in detection significance compared to previous analyses of the 1-year WMAP data release. I compare the cross-correlation results for a number of clusters to their SZ β-model profiles estimated from ROSAT and Chandra X-ray data. I conclude that the SZ profiles estimated from the β -model over-predict the observed SZ effect in the cluster samples. Additionally, I develop colour cuts using the SDSS optical bands to photometrically select emission line galaxies at redshifts of z < 0.35, 0.35 < z < 0.55 and z > 0.55. The selections have been calibrated using a combination of photometric redshifts from the COMBO-17 survey and spectroscopic observations. I estimate correlation lengths of rо = 2.64 (^+2.64_-0.08) h (^-1) Mpc, ro = 3.62 > ± 0.06h (^-1) and rо = 5.88 ± 0.12h (^-1)Mpc for the low, mid and high redshift samples respectively. Using these photometric samples I search for the Integrated Sachs- Wolfe signal in the WMAP 5yr data, but find no significant detection. I also present a survey of star-forming galaxies at z ≈ 3. Using Lyman Break and U-dropout photometric elections, we identify a total of ≈ 21,000 candidate z > 2 galaxies and perform spectroscopic observations of a selection of these candidates with integration times of 10,000s with the VLT VIMOS. In total this survey has so far produced a total of 1149 LBGs at redshifts of 2 < z < 3.5 over a total area of l.18deg(^2), with a mean redshift of ž = 2.87 ± 0.34. Using both the photometric and spectroscopic LBG catalogues, I investigate the clustering properties of the z > 2 galaxy sample using the angular correlation function, measuring a clustering amplitude of rо = 4.32(^+0.13_-0.12)h (^-1) Mpc with a slope of ϒ2 = 1.90 (^+0.09_-0.14) at separations of r > 0.4h(+-1) Mpc. We then measure the redshift space clustering based on the spectroscopically observed sample and estimate the infall parameter, β, of the sample by fitting a redshift space distortion model to the ع (σ, π). To conclude this work, I analyze the correlation of LBGs with the Lya forest transmissivity of a number of z ~ 3 QSOs, with the aim of looking for the imprint of high velocity winds on the IGM. The data show a fall in the transmissivity in the Lya forest at scales of 5h(^-1)Mpc < r < 10h(^-1)Mpc away from LBGs, indicating an increase in gas densities at these scales. However we find no significant change from the mean transmissivity at scales of <3h(^-1)Mpc, potentially signifying the presence of low density ionised regions close to LBGs.

The co-evolution of galaxies and the intergalactic medium as a function of environment is studied using hydrodynamic simulations of the ACDM cosmogony. It is demonstrated with non-radiative calculations that, in the absence of non-gravitational mechanisms, dark matter haloes accrete a near-universal fraction (~ 0.9Ω(_b)/ Ω (_m))of baryons. The absence of a mass or redshift dependence of this fraction augurs well for parameter tests that use X-ray clusters as cosmological probes. Moreover, this result indicates that non- gravitational processes must efficiently regulate the formation of stars in dark matter haloes if the halo mass function is to be reconciled with the observed galaxy luminosity function. Simulations featuring stellar evolution and non-gravitational feedback mechanisms (photo-heating by the ultraviolet background, and thermal and kinetic supemovae feedback) are used to follow the evolution of star formation, and the thermo- and chemo- dynamical evolution of baryons. The observed star formation history of the Universe is reproduced, except at low redshift where it is overestimated by a factor of a few, possibly indicating the need for feedback from active galactic nuclei to quench cooling flows around massive galaxies. The simulations more accurately reproduce the observed abundance of galaxies with late-type morphologies than has been reported elsewhere. The unique initial conditions of these simulations, based on the Millennium Simulation, allow an unprecedented study of the role of large-scale environment to be conducted. The cosmic star formation rate density is found to vary by an order of magnitude across the extremes of environment expected in the local Universe. The mass fraction of baryons in the observationally elusive warm-hot intergalactic medium (WHIM), and the volume filling factor that this gas occupies, is also shown to vary by a factor of a few across such environments. This variation is attributed to differences in the halo mass functions of the environments. Finally, we compare the X-ray properties of haloes from the simulations with the predictions of the White and Frenk (1991) analytic galaxy formation model, and demonstrate that deviations from the analytic prediction arise from the assumptions i) that haloes retain their cosmic share of baryons, and ii) their gas follows an isothermal density profile. The simulations indicate that a significant fraction of gas is ejected from low mass haloes by galactic superwinds, leading to a significant increase in their cooling time profiles and an associated drop in their soft X-ray luminosities, relative to the analytic model. Simulated X-ray luminosities remain greater than present observational upper limits, but it is argued that the observations provide only weak constraints and may suffer from a systematic bias, such that the mass of the halo hosting a given galaxy is overestimated. This bias also follows from the assumption that haloes exhibit isothermal density profiles.

In this thesis, we study the evolution of radio luminosity functions (RLF) for AGN and star forming galaxies (SFG), the colour-magnitude distributions of radio and X-ray sources at redshift z ~1, the star formation rate density in dwarf galaxies at z ~1 and investigate downsizing. In chapter 1 we give the background to our studies. We describe the Big Bang model before going on to examine different types of galaxies and looking at their star formation rates and the variation of their properties with their envirorunents. We summarise the elements of modern astronomy methodology used throughout this thesis in chapter 2. In this chapter we describe the methods of measuring star formation rates, galaxy environments and luminosity functions. In chapter 3 we match the AEGIS20 radio survey to the DEEP2 optical spectroscopic survey in the extended Groth Strip (EGS) to create a sample of radio-emitting galaxies that we separate into AGN and SFGs. We derive the RLFs of each of these at two redshift intervals and measure their evolution out to z ~1. We also compare the colour-magnitude distribution of the radio sources to that of the general galaxy population at this redshift and compare these to their local Universe equivalents. We found the evolution of the RLFs to be consistent with pure luminosity evolution with the form L x (1 + z)(^a) where a = 1.0 ± 0.9 for the AGN and a = 3.7 ± 0.3 for the SFGs. We analyse the variations of these radio sources' properties with their environments in chapter 4. Using the projected n(^th) nearest neighbour method to estimate the density of the environments, we find a strong trend of SFG numbers dropping with density. The final science chapter is chapter 5 in which we describe the Redshift One LDSS3 Emission-line Survey (ROLES). This survey targets the [OII] emission line in dwarf galaxies with log (M(_*)/M(_ʘ) )<9.5. We convert the [OII] luminosity to a star formation rate (SFR) and then proceed to analyse the mass-dependence of the global star formation rate at redshift z ~ 1 We find that SFR turns over with stellar mass at this redshift. By also comparing to similar studies in the local Universe, we investigate the empirical "downsizing" picture of galaxy evolution. Finally, we present our conclusions and suggestions for future work in chapter 6.

We have investigated the 2D 2-point correlation function, ƐAG, between low column density Lya absorbers and galaxies at a redshift z ~ 1 for the first time. 141 Lya absorbers between redshifts z = 0.68 → 1.51 over a total redshift path length of ∆z = 1.09 were collected from HST STIS E230M absorption spectra towards the quasars HE 1122-1648 (z = 2.4) and PKS 1127-145 (z = 1.187). The column density of the correlated Lya absorbers ranged from 13.18 ≤ log(_10) (N(_HI) (cm(^-2))) ≤ 17.42, with a median column density of log(_10) (N(_HI) (cm(^-2))) 13.99 ± 0.21. A total of 200 galaxy redshifts within the surrounding 6.8' x 5.7' field of view of both quasars were identified in a R magnitude limited survey (21.5 ≤ R(_vega) ≤ 24.5) using the FORS2 spectrograph at the VLT. An upper-limit of Ɛ(_AG) = 18.3 was found when 194 Lya absorber-galaxy pairs were binned in redshift space, in a bin of size ∆σ = 1.0, ∆π= 2.0 h(^-1_70) Mpc along the projected separation and line of sight distances respectively. The upper-limit in the cross-correlation was found to be 3.2σ lower than the central peak in the galaxy auto-correlation, Ɛ’(_GG), which was equal to 3.89 ± 0.65, and » 5σ lower than the galaxy auto-correlation that was measured by the 2dFGRS and VVDS investigations. Thus we measured clustering amongst galaxies to be significantly stronger than the clustering between low column density Lya absorbers and galaxies. We then used GIMIC, a high-resolution hydrodynamical simulation, to re-create the cross-correlation. When binned with ∆σ= 1.0, ∆π = 2.0 h(^-1_73)Mpc in redshift space the simulations were consistent with the observations. No significant correlation exists between galaxies and Lya absorbers with log(_10) (N(_HI) (cm(^-2)))= 13 - 17, and ƐAG had a peak of 2.65 ± 0.78 at a redshift z = 1.0. The simulated Ɛag was observed to only marginally increase when measured with absorbers of an increasing column density between log(_10) (N(_HI) (cm(^-2)))- 13 - 17. Likewise Ɛag increased by < lσ to 3.96 ± 1.21 when the cross-correlation was measured at z = 0.5. Hence in the models there is no significant evolution in Ɛag with redshift. Ɛ GG from the GIMIC simulation was 27.05 ± 4.06 at z = 1.0, so when plotted in redshift space Ɛgg was again significantly greater than the cross-correlation. Thus we reached a conclusion that the galaxies that inhabit the nodes and filaments of the dark matter cosmic web are embedded within, but not necessarily correlated with the low column density Lya absorbers (log(_10) (N(_HI) (cm(^-2)))< 17) that loosely trace this filamentary structure. Hence the Lya absorption fines in quasar spectra are predominantly caused by photons passing through this diffuse medium, and not because the sightline passes through a galaxy halo. In a small side study, 47 C IV and 18 O VI absorption lines located in the UVES spectra of quasars HE 1122-1648 and PKS 1127-145 were used to calculate the oxygen and carbon metallicity of the Lya absorbers. We found no evolution with redshift for either species. The mean carbon solar metallicity between 1.0 < z < 2.35 was [C/H]= (-0.05±0.34)z-1.24±0.58. There was a large scatter that varied from solar abundances to [C/H]-3.41(^+0.12_-0.09). The mean oxygen solar metallicity between 2.0 < z < 2.4 was [0/H]= (1.01 ± 1.54)z - 3.94 ± 3.35, again with a similar large scatter in the oxygen abundance. These results are similar to previous findings by Schaye et al. (2003) and Aguirre et al. (2008), who studying C IV and O VI lines from 19 quasars at similar redshifts also found no significant evolution in the metallicity. All of these results indicate that many of these metals must have been expelled into the IGM at higher redshifts

In this thesis the spectroscopic and photometric results of the Galactic and extragalactic globular clusters are presented. And their implications on galaxy formation have been investigated. Integrated spectroscopy with a high resolution of 24 Galactic globular clusters were obtained using the Isacc Newton Telescope, from which 21 line indices were carefully measured and calibrated. By comparing with recent simple stellar population models (Thomas et al. 2003 and Lee &amp; Worthey 2005), it is confirmed that Galactic globular clusters are old (~10- 12 Gyr). There is a discrepancy between the two models in low metallicity and the line indices measured have a better fit to Lee & Worthey (2005) model. These is a significant effect of blue horizontal branch stars on the Balmer absorption lines in integrated spectra, which could cause globular clusters to be underestimated their age. Shell in elliptical galaxies are probably signature of recent galaxy merger/interaction. Properties of globular cluster systems (GCSs) in six shell galaxies have been examined and whether this signature can be seen in GCSs have been investigated. The GCSs in shell galaxies are found not to differ noticeably from those in normal elliptical galaxies in the sense and blue subpopulations are consistent with previous studies. This result is contradictory to results by Sikkema et al. (2006), who have found possible young globular clusters in the two galaxies. Using the Advanced Camera for Survey on the Hubble Space telescope, 10 low density early-type galaxies were observed and properties of their GCSs have been investigated to constrain galaxy formation history depending on environments. By comparing results from the Virgo Cluster Survey as a high-density counterpart, both similarities and differences between the two density groups were found. General behaviour of colour distributions of GCSs found in cluster environment are also seen in those in field galaxies; mean colour gets redder as increasing with galaxy luminosity, less bimodal colour distributions are detected in lower galaxy luminosity, and there is a correlation between red colour peak and host galaxy luminosity. However, mean colours of GCS in low-density appear to be slightly bluer than those in high-density at a given galaxy luminosity, which implies that GCS in field environments is either less metal-rich or younger than those in cluster environments. More diverse shape of colour distributions are found in dense region than in low-density region, which would reflects more complicated galaxy formation history in dense region. In spite of finding environmental this effect on galaxy formation, this effect is so subtle that galaxy (final) mass is still a dominant factor to determine galaxy formation and stellar populations in there.

X-ray astronomers currently have access to two major X-ray observatories, XMM-Newton and Chandra. While targeted observations are likely to continue for the next few years, this will not be the case forever. Archival data will thus become an increasingly important resource. X-ray observations produce large samples of active galaxies with fewer biases than at other wavelengths. In this thesis, techniques for archival survey work are developed and applied to small 'pilot' samples of AGN from the XMM-Newton archive. A photometric redshift method for use with X-ray selected AGN is developed and tested with both faint and bright samples (from the Lockman Hole region and 2XMM serendipitous catalogue respectively). A level of accuracy surpassing other X-ray photometric redshift methods is found. A deep look at the 3C 273 field from multiple XMM-Newton observations is used to investigate continuum X-ray variability in serendipitous AGN in the field. The photometric redshift method developed is used to determine X-ray luminosities for the serendipitous sources and the commonly found anti-correlation between excess variance and X-ray luminosity is reproduced. The connection between continuum variability in the X-ray and optical/UV bands is investigated using a sample of Seyfert 1 galaxies from the XMM-Newton Science Archive. Cross correlation analysis of the light curves on timescales of ≈1000s finds no significant evidence for correlation between the bands. A larger sample of sources is taken from the serendipitous source catalogue 2XMMp to investigate cosmic variance and bias of X-ray selected sources. For full band (0.2 - 12 keV) sources above a flux limit of l x 10-14 erg cm-2 S-1, AGN bias, which characterises how AGN mass traces the underlying mass, is found to be in agreement (within the error bounds) with the bias factor determined from much larger optical surveys.

This thesis presents an X-ray and optical analysis of the Subaru XMM-Newton Deep Survey (SXDS), focusing on the analysis of the combined XMM-Newton and INT-WFC data. The SXDS has an unprecedented combination of depth and area coverage, covering 1.3 square degrees, making this survey the largest ultra-deep survey to date. The vast majority of the &ap; 1000 X-ray sources within the survey are found to be active galactic nuclei (AGN), making this an excellent resources for investigating the distribution of unobscured and obscured sources.;Concentrating on the AGN population, cross-correlation of X-ray, optical and spectroscopic data have enabled investigation into optical and X-ray colours, optical morphologies, redshift distribution and X-ray and optical obscuration. This thesis, utilizing underlying X-ray and optical properties of AGN such as central nucleus luminosity and obscuration also introduces a simple toy model with the aim of understanding the SXDS AGN X-ray-to-optical flux ratio distribution.;XMM-Newton's large field of view and SXDS field depth has also enabled investigations into the X-ray spectral properties of the brightest 130 sources (> 300 total EPIC counts) within the SXDS. These sources are shown to mainly comprise of unobscured and obscured AGN with a range of intrinsic absorptions and best filling photon indices of ? &ap; 1.8 -- 2.0, consistent with other X-ray surveys.;To illustrate the capabilities of XMM-Newton the X-ray source properties of two powerful, high redshift (z = 2.48) narrow line radio-loud type-2 quasars B3 0731+438 and 3C 257, observed separately from the SXDS are also presented.;The combined optical and X-ray analysis presented in this thesis reveals the SXDS AGN population comprise of a large population of unobscured and obscured AGN. These sources have a range of absorption columns, redshifts and luminosities, encompassing low luminosity AGN through to luminous quasars and demonstrate a strong relationship between optical and X-ray obscuration.

This thesis is concerned with multi-wavelength observations of the prominent southern hemisphere high energy BL Lac object, (HBL), PKS 2155-304. After a general introduction covering the particulars of Active Galactic Nuclei, the pysical processes and models that are believed to play an important role in the observations and ground based γ-ray astronomy, the results and interpretation of four individual multi-wavelength campaigns on PKS 2155-304 are presented. Lead by observations of the High Energy Stereoscopic System (H.E.S.S.), these campaigns include observations with RXTE, NTT at ESO, ROTSE, Spitzer, JCMT and the NRT. During all these campaigns, the source appeared to be in a quiescent state, allowing us to probe the jet paramaters and emission models for a quiescent HBL for the first time. The models for VHE emission from HBLs have evolved over the last 14 years since Mkn 421 was detected as a VHE emitter. However, the sensitivity of the past generations of VHE telescopes has only been sufficient to observe VHE emission from HBLs during apparent active states. These evolved models are therefore essentially high active state emission models. Since the sensitivity of H.E.S.S. now allows us to detect these objects in a quiescent state , the obvious question is, do the 'active state' models still accurately predict the SED and in particular the VHE emission?

It has become increasingly apparent that active galactic nuclei (AGN) have played a key role in the galaxy formation process, leading to the galaxy population we see to day. In order to understand better this inter-relationship, we must first measure the characteristics and evolution of the AGN population over cosmic timescales. Models of the AGN population which reproduce the spectrum and intensity of the extra-galactic X-ray background require a large population of faint AGN, the majority obscured by large column densities of cold material. In the local Universe, where we find mostly low luminosity objects, the obscured AGN make up 80% of the population. However, at higher redshifts, including the epoch when AGN and galaxies were forming most rapidly, the demographics of the obscured AGN population are still poorly understood. For this thesis, I have made a detailed examination of the AGN detected in several of the deepest XMM-Newton "blank-field" observations. I have carried out a detailed set of Monte-Carlo simulations in order to compare directly the X-ray properties of the observed AGN to the predictions of a number of AGN population models. For sources detected in the "13H" deep field, I find that the best fitting model contains AGN with a broad range of obscuration levels, but with significantly absorbed AGN making up at least 75% of the population. Furthermore, by examining the sources in XMM-Newton observations of the "CDFS" field, for which nearly complete redshift determinations are available, I find that the AGN absorption distribution exhibits little redshift or luminosity dependence. I confirm these findings by extending my study to a much larger AGN sample, and investigate field-to-field AGN source density variations.