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This thesis examines properties of galaxies in and around compact groups. Astrometry, photometry and morphological classifications are derived from CCD images for all 463 galaxies in Hickson's sample of 100 compact groups. Some minor revisions to the membership of the original catalog are made. At high galactic latitude (b > 30°), the catalog is estimated to be 90% complete for groups with total B[formula omitted] magnitude 13.0 or less. 49% of all the catalogued galaxies, and 48% of first-ranked galaxies are spiral. No significant difference is found between the distribution of morphological types of first-ranked galaxies and all group galaxies. Morphological concordance occurs among galaxies within a group: more galaxies are the same type (spiral or nonspiral), than would be expected by chance. Galaxy morphological type correlates with group optical luminosity and, more strongly, with velocity dispersion, but not with galaxy space density. These results imply that the morphological types of galaxies in compact groups are strongly influenced by the environment, and that this influence occurs mostly at the time of galaxy formation. Fields surrounding 97 compact groups with known redshifts were examined on the Palomar Observatory Sky Survey prints. 3889 galaxies were identified within 1.125h⁻¹ Mpc of the centre of each group. Coordinates, magnitudes, diameters, and Hubble types are derived for these galaxies. 78% of the groups show no significant excess of field galaxies within 0.5h⁻¹ Mpc. This indicates that most compact groups are truly isolated. 59% of these field galaxies were classified as spiral, a higher fraction that for the group galaxies. This difference is more pronounced for groups which do show a significant field galaxy excess. These results indicate that most groups are dense dynamical entities. Monte-Carlo calculations indicate that 35% of galaxy quintets are predicted to contain a single discordant redshift due to the chance alignment of an unrelated field galaxy. This is in agreement with the observed number of four discordant quintets in 10. These results are consistent with the cosmological interpretation of galaxy redshifts. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The properties of galaxy clusters, such as abundance and mass to light ratios, have long been used to investigate and constrain cosmology. With vast numbers of newly detected clusters, such as from the Planck mission (Planck Collaboration et al., 2013), full determination of cluster properties, particularly mass, can be hugely expensive and time consuming. Optical characterisation o ers a cheap solution, using optical data alone to estimate cluster properties such as redshift. With the abundance of current optical data, such as from the Sloan Digital Sky Survey (SDSS), (Ahn et al., 2012) and upcoming all sky surveys, such as the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) 3 survey (Magnier et al., 2013), optical characterisation will play a key role in the investigation of the latest clusters. Presented in this thesis is the Gaussian Mixture full Photometric Red sequence Cluster Characteriser (GMPhoRCC), which aims to provide such an analysis, o ering substantial advantages over existing algorithms. GMPhoRCC identi es and models the red sequence, early-type galaxies which dominate the cluster, and uses the properties of this to estimate cluster redshift and richness, an optical mass proxy based on the number of cluster members. The main features include, full treatment of multi-modal distributions by modelling properties with error-corrected Gaussian Mixtures, model independence by using empirical photometric redshifts rather than assumed colour-redshift relations and quality control used to identify probable catastrophic failures in order to clean the characterisations. Using a sample of 5500 clusters taken from the GMBCG (Hao et al., 2010), NORAS (Bohringer et al., 2000), REFLEX (Bohringer et al., 2004) and XCS (Mehrtens et al., 2012) catalogues, GMPhoRCC redshift estimates are compared to spectra showing low scatter ( σ∆z~ 0:042) around the actual value. In addition applying the quality control to produce a clean subset removes most outliers (|zGMPhoRCC-zspec| > 0:03) gives a much tighter agreement, σ∆z~ 0:018 showing signi cant improvement over maxBCG, σ∆z~ 0:025, and XCS, σ∆z~ 0:050. In addition to comparisons with real clusters, an extensive evaluation of the GMPhoRCC selection function is presented using mock clusters. These mocks are produced by stacking red sequence galaxies from existing clusters, analysed using the SDSS DR9, in redshift-richness bins from which new sequences are resampled. This extends the similar approach of maxBCG and GMBCG where only rich clusters are used as seeds to generate mocks with a range of properties. Comparisons with mocks agree well with real clusters attaining low redshift scatters ( σ∆z~ 0:01) with the clean subset removing the majority of outliers. In addition, with a de nitive mock value, richness comparisons are possible and although show a larger fractional scatter (σ∆z n200 ~ 0:12) are centred on the mock value. Richness estimates are shown to be more sensitive to discrepancies in redshift, background uctuations and poor modelling of the red sequence than redshift. Completeness is estimated by considering the fraction of clusters found with characterisations within given bounds. First incomplete photometry, simulated by an i-band < 21 cut, is shown to remove members for clusters with z > 0:45. Redshift completeness, the fraction of clusters within 0:03 of the mock value, is not immediately hindered by the photometry, attaining 93% for 0:05 < z < 0:62 for clusters with a richness greater than 20, showing improvement over maxBCG (with 90% for 0:1 < z < 0:3) and a larger range than GMBCG (with 96% for 0:1 < z < 0:46). Similar to results from GMBCG, richness attains lower completeness rates due to discrepancies introduced by projection e ects, background uctuations, and redshift errors. The fraction of clusters within 25% of the mock value, de ning completeness, is measured as 91% for 0:07 < z < 0:45 for clusters with richness greater than 20, 78% for those with richness between 10 and 20, and 64% for those with richnesses less than 10. The application of GMPhoRCC follows, where characterisations are found for new XCS X-ray extended sources (Lloyd-Davies et al., 2011). Applying GMPhoRCC to these preliminary DR2 candidates ( 10 times larger than the current catalogue) using the VLT Survey Telescope (VST) ATLAS catalogue (Shanks & Metcalfe, 2012) and the much deeper Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) (Heymans et al., 2012) provides characterisations beyond the SDSS footprint. Of the 13; 956 candidates, 6124 have optical coverage, 5580 in the SDSS, 523 in ATLAS and 819 in CFHTLenS with some overlap. Overall characterisations are found for 4365 candidates, 1893 of which have an associated spectroscopic redshift. The clean subset comprises 1203 candidates, 904 with spectra. Considering XCS DR1, Mehrtens et al. (2012) presented 503 optically con rmed X-ray clusters of which 258 have spectroscopic redshifts and 108 have SDSS characterisations. GMPhoRCC provides characterisations for 360, 232 of which have spectroscopic redshifts. Overall GMPhoRCC provides 260 (149 of which are clean) new SDSS characterisations and 91 (61 of which are clean) new spectroscopic redshifts. Finally this thesis concludes with a discussion of future research, focusing mainly on a preliminary analysis of a clean spectroscopic subset of XCS DR1 in order to illustrate the potential to constrain X-ray scaling relations with the upcoming XCS DR2. Additionally, potential research into the e ect of environment on the red sequence is illustrated using the dependence of the CMR slope on X-ray temperature. While a slight dependence is found, the cluster sample is insu cient to contradict the independence on environment found by Hogg et al. (2004) and Hao et al. (2009).

I present spectroscopic imaging of the high-velocity system (HVS) towards the central cD galaxy (NGC 1275) in the Perseus Cluster at a high spectral resolution for the first time. Previous observation suggests that the HVS is a highly inclined dusty and gas-rich galaxy moving towards the center of NGC 1275 at a high speed of 3000 km/s relative to the systemic velocity of NGC 1275 through the hot intracluster medium (ICM). If this is the case, then the HVS should be undergoing intense ram-pressure stripping. However, there is tentative evidence for ram-pressure stripping in the HVS, and furthermore confined to a small region of the galaxy. Previous observations also point out that at the location where the HVS is seen, there are many star clusters seen towards the inner region of NGC 1275. The separation of young star clusters between those belong to NGC 1275 and those belong to the HVS is, however, not clearly defined. The primary scientific objectives are to (i) search for evidence for ram-pressure stripping in the HVS, as well as signs of tidal interactions between the HVS and NGC 1275; and (ii) separate the numerous young star clusters seen towards the entire NGC 1275 into those associated with the HVS and those associated with NGC 1275. NGC 1275 and the HVS were observed simultaneously with the use of Potsdam Multi-Aperture Spectrophotometer. The main emission lines being studied are the Hα & [NII]λ6548,6483 lines in NGC 1275 and the HVS. I present maps of intensity distribution, velocity field and velocity dispersion of the Hαemission of the HVS, as well as the line ratio of the [NII] doublets lines to the Hα line in the HVS. I find that the line ratio of [NII]/Hα is less than 0.1 throughout the entire body of the HVS, indicating metallicity is low in the HVS. I also find that the metallicity is decreasing with distance from the center, just like other normal spiral galaxies. I demonstrate that a large fraction of the young star clusters seen towards the inner regions of NGC 1275 are closely associated with bright Hα-emitting regions in the HVS, and trace the overall Hα-emitting body of the HVS, suggesting that some young star clusters are associated to the HVS. I find that there are two distributions of young star clusters in color-color space, providing a way to separate out the star clusters likely belong to the HVS. I present evidence that the HVS is experiencing intense ram-pressure stripping and also evidence suggesting that the HVS is possibly tidally interacting with NGC 1275. The results demonstrate that the HVS is a dusty, gas-rich, low-metallicity galaxy that has been disrupted by ram-pressure stripping and possibly also tidal interactions. I show that the HVS exhibit widespread and vigorous (~3.6 MM_⊙ yr^(-1)) star formation over the last at least ~0.1 Gyr. The vigorous SFR of the HVS is in contrast to what suggested by the observed low metallicity (suggestive of relatively weak star-formation activity over the recent history). The SFR of the HVS is likely to be triggered by the same process that produces global distortion on the HVS, here ram pressure stripping and possibly tidal interaction are in consideration. / published_or_final_version / Physics / Master / Master of Philosophy

The evolution of radio loud quasars is found to be strongly dependent upon their galaxy cluster environment. Previous studies (Yee and Green 1987) have shown that bright quasars at z ∼ 0.6 are found in clusters as rich as Abell richness class 1, while high luminosity quasars at lower redshifts are found only in poorer environments. An observational study of the environments of 66 low luminosity quasars with 0.3 < z < 0.6 yields several objects in rich clusters of galaxies. This result implies that radio loud quasars in these environments have faded approximately 3 magnitudes in the interval between redshifts 0.6 and 0.4, corresponding to a luminosity e-folding fading time of 900 million years, similar to the dynamical timescale of these environments. The analysis of low luminosity radio quiet quasars indicate that they are never found in rich environments, suggesting that they are a physically different class of objects. Properties of the quasar environment are investigated to determine constraints on the physical mechanisms of quasar formation and evolution. The optical cluster morphology indicates that the cluster cores have smaller radii and higher galaxy densities than are typical for low redshift clusters of similar richness. Radio morphologies may indicate that the formation of a dense intra-cluster medium is associated with the quasars' fading at these epochs. Galaxy colors appear to be normal, but there may be a tendency for clusters associated with high luminosity quasars to contain a higher fraction of gas-rich galaxies than those associated with low luminosity quasars, a result consistent with the formation of an ICM. Multislit spectroscopic observations of galaxies associated with high luminosity quasars indicate that quasars are preferentially located in regions of low relative velocity dispersion, either in rich clusters of abnormally low velocity dispersion, or in poor groups which are dynamically normal. This suggests that galaxy-galaxy interactions may play a role in quasar formation and sustenance. Virialization of rich clusters and the subsequent increase in galaxy velocities may therefore be responsible for the fading of quasars in rich environments.

We describe updates to the redMaPPer algorithm, a photometric red-sequence cluster finder specifically designed for large photometric surveys. The updated algorithm is applied to 150 deg(2) of Science Verification (SV) data from the Dark Energy Survey (DES), and to the Sloan Digital Sky Survey (SDSS) DR8 photometric data set. The DES SV catalog is locally volume limited and contains 786 clusters with richness lambda > 20 (roughly equivalent to M500c greater than or similar to 10(14) h(70)(-1)M(circle dot)) and 0.2 < z < 0.9. The DR8 catalog consists of 26,311 clusters with 0.08 < z < 0.6, with a sharply increasing richness threshold as a function of redshift for z greater than or similar to 0.35. The photometric redshift performance of both catalogs is shown to be excellent, with photometric redshift uncertainties controlled at the sigma(z)/(1+ z) similar to 0.01 level for z greater than or similar to 0.7, rising to similar to 0.02 at z similar to 0.9 in DES SV. We make use of Chandra and XMM X-ray and South Pole Telescope Sunyaev-Zeldovich data to show that the centering performance and mass-richness scatter are consistent with expectations based on prior runs of redMaPPer on SDSS data. We also show how the redMaPPer photo-z and richness estimates are relatively insensitive to imperfect star/galaxy separation and small-scale star masks.

Bright optical nebulae are a relatively common feature of galaxy clusters with a central depression in their intracluster gas temperature suggestive of an X-ray cooling flow. In my thesis, I have measured, for the first time, the velocity field of nearly the entire optical nebula associated with NGC 1275, the central cD (giant elliptical) galaxy of the Perseus cluster. This nebula is the brightest example with the largest projected size in the sky. Our primary scientific objective is to address the physical processes that give rise to the complex morphology of this nebula, which comprises a multitude of mostly approximately radial but also a number of tangential emission-line _laments. This nebula spans up to ～140 kpc in the north-south direction, extending far beyond the half-light radius of NGC 1275. Popular models for the nature of the nebula invoke either an X-ray cooling flow, in which case the filaments should possess a velocity profile consistent with free fall, or gas drawn out from the central galaxy by buoyantly rising bubbles inflated by radio jets from the AGN, in which case the filaments should show a reversal in velocity along their lengths. We find that the velocity field of the nebula is incredibly complex, and in several important respects contradicts model predictions based on slit spectroscopy. We find that filaments previously thought to be very long integral structures actually comprise multiple shorter filaments that each have their own distinct kinematics. Furthermore, filaments that are apparently aligned and adjacent to each other often possess entirely different kinematics. We searched for filaments with velocity profiles consistent with free fall, but we could only find very few examples beyond the central bright nebular region where overlapping filaments complicate measurements of the individual filament kinematics. We also searched for filaments that show a reversal in velocity along their lengths, but again could find only several examples. Although the combination of a residual X-ray cooling flow and relatively cool gas drawn out by buoyant X-ray bubbles remains the most viable explanation for the nature of the nebula, both the morphology and kinematics of this nebula is complicated by the action of various X-ray bubbles that are currently expanding or rising through the nebula. As such, the velocity field of the filaments reflect the effects of the X-ray bubbles on the bulk flows within the intracluster medium, and trace streamlines that reveal motions in the surrounding X-ray gas. We point out evidences that support the idea that some filaments are being dragged by rising X-ray bubbles, others represent large-scale vortices behind bubbles, and yet others are draping the surface of and pushed outwards by expanding X-ray bubbles. / published_or_final_version / Physics / Master / Master of Philosophy

No description available.

We present the 1.4-GHz catalog of the galaxy cluster field RCS J022434-0002.5, at a redshift of z = 0.773. A total of 194 sources were found within a &sim;0.28 degree2 region to a 5sigma depth of &sim;75 muJy. We show that the differential source counts for the cluster field are in good agreement with other radio surveys, and therefore do not indicate a strong excess of radio sources in the cluster compared to the field. We find 13 sources have optical counterparts with photometric redshifts within 1sigma of the cluster redshift and an additional 5 within 2sigma, and we consider these objects to be candidate cluster members. We use their radio luminosities to attempt to diagnose the presence of active galactic nuclei or star formation activity. We find that the cluster candidates are statistically more likely to be powered by active galactic nuclei, rather than star formation.