Influence of cosmological expansion in local experiments

Whether the cosmological expansion can influence the local dynamics, below the galaxy clusters scale, has been the subject of intense investigations in the past three decades. In this work, we consider McVittie and Kottler spacetimes, embedding a spherical object in a FLRW spacetime. We calculate the influence of the cosmological expansion on the frequency shift of a resonator and estimate its effect on the exchange of light signals between local observers. In passing, we also clarify some of the statements made in the literature.

A GMRT Narrowband vs. Wideband Analysis of the ACT-CL J0034.40225 Field Selected from the ACTPol Cluster Sample+

Low frequency radio observations of galaxy clusters are a useful probe of the non-thermal intracluster medium (ICM), through observations of diffuse radio emission such as radio halos and relics. Current formation theories cannot fully account for some of the observed properties of this emission. In this study, we focus on the development of interferometric techniques for extracting extended, faint diffuse emissions in the presence of bright, compact sources in wide-field and broadband continuum imaging data. We aim to apply these techniques to the study of radio halos, relics and radio mini-halos using a uniformly selected and complete sample of galaxy clusters selected via the Sunyaev-Zel’dovich (SZ) effect by the Atacama Cosmology Telescope (ACT) project, and its polarimetric extension (ACTPol). We use the upgraded Giant Metrewave Radio Telescope (uGMRT) for targeted radio observations of a sample of 40 clusters. We present an overview of our sample, confirm the detection of a radio halo in ACT−CL J0034.4+0225, and compare the narrowband and wideband analysis results for this cluster. Due to the complexity of the ACT−CL J0034.4+0225 field, we use three pipelines to process the wideband data. We conclude that the experimental spam wideband pipeline produces the best results for this particular field. However, due to the severe artefacts in the field, further analysis is required to improve the image quality.

Exploring Diffuse Radio Emission in the Southern Sky

<p>This thesis investigates currently observed correlations between the thermal and non-thermal (radio halos) components of galaxy clusters, and seeks to verify the reliability of the proposed radio halo scaling relations presented in the literature. It employs a two-pronged approach: 1) a statistical examination of 15 galaxy clusters; and 2) detailed multi-wavelength analysis of individual objects of interest. We first investigated radio data for 15 galaxy clusters drawn from the parent REXCESS sample observed with the ATCA at 1.4 GHz to conduct a radio halo survey. Examination of available and re-processed low resolution images revealed cluster-scale diffuse objects in three clusters. One was a radio halo candidate in Abell 3888 (A3888), with the two remaining diffuse sources being radio relic candidates. Follow-up observations of the candidate clusters were performed in July and December 2011, and March 2012, with the upgraded ATCA (CABB). Radio observations with CABB in different array configurations were used to provide the required resolution and sensitivity to a wider range of angular scales to probe the candidate diffuse sources. Examination of the final CABB images confirmed the existence of the radio halo in A3888; however, the remaining candidates were found to be a head-tail galaxy and a very bright radio galaxy with extended emission. As this thesis presents some of the earliest CABB observations, new data reduction and imaging procedures were necessarily developed and presented here. The statistical component of this thesis uses a halo sample obtained from the combined detection of this work and the literature to derive new correlations between the cluster observables and the radio halo power. The new correlation between the X-ray luminosity and radio halo power derived here is flatter than the previous correlation in the literature, suggesting that massive clusters may host lower power halos than previously thought. In addition, we derived the upper limits of the undetected power of possible radio halos for our non-halo clusters via injection of fake radio halos into the UV data. Our derived upper limits with respect to the anticipated halo powers according to the previous and new correlations and their interpretations are discussed in the thesis. The distribution of the combined upper limits (this work and the literature) compared to our new correlation shows no sign of the strong bi-modality found in the literature. As previously mentioned, we detected a giant radio halo in A3888. We observed A3888 with the AAOmega spectrograph to infer the dynamics of the cluster. We measured the spectra of 254 galaxies within a 300 radius from the core of A3888 and combined these data with the available literature redshifts in the region. We identified 71 member galaxies of A3888 and examined the density contours, which indicated that the distribution of the member galaxies is elongated along an east-west axis. This elongation might be indicative of dynamical interactions in the cluster; however, there is no statistically significant deviation from Gaussianity in the velocity data. We then carried out a Lee-Fitchett 3D substructure test and found that A3888 is bimodal and has two subgroups. The head-tail galaxy mentioned earlier in one of the clusters was originally thought to be a radio relic candidate. Owing to available broadband polarimetric data and well-separated jets of the head-tail galaxy, we investigated the magnetic field direction of the head-tail galaxy and conclude it is highly likely that a helical magnetic field is present in the jets. We present the high-resolution images of our 15 clusters and create a catalogue of the detected sources. Finally, we discuss concerns with the current radio halo detections in the literature, and how radio halo surveys could be designed in the future to yield unbiased results.</p>

Exploring Diffuse Radio Emission in the Southern Sky

<p>This thesis investigates currently observed correlations between the thermal and non-thermal (radio halos) components of galaxy clusters, and seeks to verify the reliability of the proposed radio halo scaling relations presented in the literature. It employs a two-pronged approach: 1) a statistical examination of 15 galaxy clusters; and 2) detailed multi-wavelength analysis of individual objects of interest. We first investigated radio data for 15 galaxy clusters drawn from the parent REXCESS sample observed with the ATCA at 1.4 GHz to conduct a radio halo survey. Examination of available and re-processed low resolution images revealed cluster-scale diffuse objects in three clusters. One was a radio halo candidate in Abell 3888 (A3888), with the two remaining diffuse sources being radio relic candidates. Follow-up observations of the candidate clusters were performed in July and December 2011, and March 2012, with the upgraded ATCA (CABB). Radio observations with CABB in different array configurations were used to provide the required resolution and sensitivity to a wider range of angular scales to probe the candidate diffuse sources. Examination of the final CABB images confirmed the existence of the radio halo in A3888; however, the remaining candidates were found to be a head-tail galaxy and a very bright radio galaxy with extended emission. As this thesis presents some of the earliest CABB observations, new data reduction and imaging procedures were necessarily developed and presented here. The statistical component of this thesis uses a halo sample obtained from the combined detection of this work and the literature to derive new correlations between the cluster observables and the radio halo power. The new correlation between the X-ray luminosity and radio halo power derived here is flatter than the previous correlation in the literature, suggesting that massive clusters may host lower power halos than previously thought. In addition, we derived the upper limits of the undetected power of possible radio halos for our non-halo clusters via injection of fake radio halos into the UV data. Our derived upper limits with respect to the anticipated halo powers according to the previous and new correlations and their interpretations are discussed in the thesis. The distribution of the combined upper limits (this work and the literature) compared to our new correlation shows no sign of the strong bi-modality found in the literature. As previously mentioned, we detected a giant radio halo in A3888. We observed A3888 with the AAOmega spectrograph to infer the dynamics of the cluster. We measured the spectra of 254 galaxies within a 300 radius from the core of A3888 and combined these data with the available literature redshifts in the region. We identified 71 member galaxies of A3888 and examined the density contours, which indicated that the distribution of the member galaxies is elongated along an east-west axis. This elongation might be indicative of dynamical interactions in the cluster; however, there is no statistically significant deviation from Gaussianity in the velocity data. We then carried out a Lee-Fitchett 3D substructure test and found that A3888 is bimodal and has two subgroups. The head-tail galaxy mentioned earlier in one of the clusters was originally thought to be a radio relic candidate. Owing to available broadband polarimetric data and well-separated jets of the head-tail galaxy, we investigated the magnetic field direction of the head-tail galaxy and conclude it is highly likely that a helical magnetic field is present in the jets. We present the high-resolution images of our 15 clusters and create a catalogue of the detected sources. Finally, we discuss concerns with the current radio halo detections in the literature, and how radio halo surveys could be designed in the future to yield unbiased results.</p>

L-GALAXIES 2020: The formation and chemical evolution of stellar haloes in Milky Way Analogues and galaxy clusters

We present an analysis of the formation and chemical evolution of stellar haloes around (a) Milky Way Analogue (MWA) galaxies and (b) galaxy clusters in the L-Galaxies 2020 semi-analytic model of galaxy evolution. Observed stellar halo properties are better reproduced when assuming a gradual stripping model for the removal of cold gas and stars from satellites, compared to an instantaneous stripping model. The slope of the stellar mass – metallicity relation for MWA stellar haloes is in good agreement with that observed in the local Universe. This extends the good agreement between L-Galaxies 2020 and metallicity observations from the gas and stars inside galaxies to those outside. Halo stars contribute on average only ∼0.1 per cent of the total circumgalactic medium (CGM) enrichment by z = 0 in MWAs, ejecting predominantly carbon produced by AGB stars. Around a quarter of MWAs have a single ‘significant progenitor’ with a mean mass of ∼ 2.3 × 109M⊙, similar to that measured for Gaia Enceladus. For galaxy clusters, L-Galaxies 2020 shows good correspondence with observations of stellar halo mass fractions, but slightly over-predicts stellar masses. Assuming a Navarro-Frenk-White profile for the stellar halo mass distribution provides the best agreement. On average, the intracluster stellar component (ICS) is responsible for 5.4 per cent of the total intracluster medium (ICM) iron enrichment, exceeding the contribution from the brightest cluster galaxy (BCG) by z = 0. We find that considering gradual stripping of satellites and realistic radial profiles is crucial for accurately modelling stellar halo formation on all scales in semi-analytic models.

THE POSSIBILITIES OF THE “CLUSTER CARTOGRAPHY” TOOL FOR THE STUDY OF THE INNER STRUCTURES OF GALAXY CLUSTERS

We describe the possibilities of the “Cluster Cartography” tool which was created for detailed study of the 2D distribution of galaxies in the clusters. The main tasks of the “Cluster Cartography” tool were the detailed study of the morphologyof galaxy clusters using the statistically significant numerical criteria as well as to detect their regular peculiarities. The tool allows to create the 2D map with positions of galaxies in the cluster field and show for each cluster member its shape and orientation as a best-fit ellipse using input catalogue data. The size of symbols for galaxies correspond to input data.It may reflect the galaxy image in arcseconds from catalogue in the map 4000×4000arcsec. Another way connects the size of the symbol with the magnitude of the galaxy. Tool is able to build the map in four modes: the symbols are dots; the symbols are circles with diameters reflected the magnitudes of galaxies; the symbols are ellipses with size reflected the magnitudesand both ellipticities and orientation from the input catalogue; the symbols illustrate the shape of galaxies in projection to the celestial sphere. The “Cluster Cartography” algorithms allow to detect the standard cases in galaxy distribution, suchas the degree of concentration to the cluster center and/or to some line on a statistically significant level using the numerical criteria. Also “Cluster Cartography” allows to detect other features, such as crosses, semi-crosses, complex crosses and short compact chains, as well as to export the list of galaxies forming the peculiarities for the futurestudy. The final version of the “Cluster Cartography” allows to realize the modern scheme for detailed morphological classification of galaxy clusters. The “Cluster Cartography” is powerful and perspective tool for study of features of galaxy clusters.