The late merging phase of a galaxy cluster : XMM EPIC Observations of A3266

We present a mosaic of five XMM-Newton observations of the nearby ($z=0.0594$) merging galaxy cluster Abell 3266. We use the spectro-imaging capabilities of \xmm to build precise (projected) temperature, entropy, pressure and Fe abundance maps. The temperature map exhibits a curved, large-scale hot region, associated with elevated entropy levels, very similar to that foreseen in numerical simulations. The pressure distribution is disturbed in the central region but is remarkably regular on large scales. The Fe abundance map indicates that metals are inhomogeneously distributed across the cluster. Using simple physical calculations and comparison with numerical simulations, we discuss in detail merging scenarios that can reconcile the observed gas density, temperature and entropy structure, and the galaxy density distribution

Joint signal extraction from galaxy clusters in X-ray and SZ surveys: A matched-filter approach

The hot ionized gas of the intra-cluster medium emits thermal radiation in the X-ray band and also distorts the cosmic microwave radiation through the Sunyaev-Zel'dovich (SZ) effect. Combining these two complementary sources of information through innovative techniques can therefore potentially improve the cluster detection rate when compared to using only one of the probes. Our aim is to build such a joint X-ray-SZ analysis tool, which will allow us to detect fainter or more distant clusters while maintaining high catalogue purity. We present a method based on matched multifrequency filters (MMF) for extracting cluster catalogues from SZ and X-ray surveys. We first designed an X-ray matched-filter method, analogous to the classical MMF developed for SZ observations. Then, we built our joint X-ray-SZ algorithm by combining our X-ray matched filter with the classical SZ-MMF, for which we used the physical relation between SZ and X-ray observations. We show that the proposed X-ray matched filter provides correct photometry results, and that the joint matched filter also provides correct photometry when the $F_{\rm X}/Y_{500}$ relation of the clusters is known. Moreover, the proposed joint algorithm provides a better signal-to-noise ratio than single-map extractions, which improves the detection rate even if we do not exactly know the $F_{\rm X}/Y_{500}$ relation. The proposed methods were tested using data from the ROSAT all-sky survey and from the Planck survey.Comment: 22 pages (before appendices), 19 figures, 3 tables, 5 appendices. Accepted for publication in A&

Characterisation of the Components in Cataclysmic Variables

This thesis presents new and archive X-ray, optical and ultraviolet observations of cataclysmic variables, and discusses the results obtained in the context of the relationship between the physical and spectral components visible. It concentrates on the eclipsing dwarf nova OY Carinae, which has been observed both in superoutburst and quiescence. Optical 'wide B' band light curves were obtained at the end of the 1994 superoutburst and on the decline. Eclipse mapping of these light curves reveals an accretion disc with a considerable physical flare (~ 10'). These are the first maps of a disc in the superoutburst state that clearly show such flaring. Contemporaneous X-ray observations were obtained with the ROSAT HRI. No eclipse of the X-ray flux was detected, a similar result to that obtained from the EXOSAT observations of the 1985 superoutburst by Naylor et al. (1988), supporting the case for the existence of a coronal component source for the X-rays in high accretion rate systems. Later ROSAT observations of OY Car in quiescence are presented. A 1994 PSPC observation allows constraints to be placed on the quiescent X-ray spectrum. OY Car returns similar values for the temperature of the emitting gas and the emission measure as its fellow eclipsing systems. It is difficult, however, to reconcile the column density inferred from the X-ray observation with that found from HST ultraviolet observations. A column density of nH = 10 22 cm 2 , found in the 'iron curtain' study by Horne et al. (1994), is not compatible with the X-ray spectrum. New optical photometry, obtained during quiescence in 1998, is used to update the orbital ephemeris of the system. A further ROSAT HRI light curve, obtained in quiescence with good phase coverage, is presented. It displays an eclipse of the X-ray flux, detected at the 13o level, which is coincident with the optical eclipse of the primary and suggests that the region of X-ray emission is comparable in size to the white dwarf. This confirms that the boundary layer region is visible in OY Car in quiescence, and, in common with similar systems, implies that the boundary layer is the source of the X-ray flux during periods of low mass accretion. The general picture of the X-ray emission from CVs, which has been built up from observations of different objects using different satellites, has thus been confirmed for the first time for the same object using the same satellite. The fact that the quiescent boundary layer can be seen, and that the soft X-ray flux is not extinguished, together suggest that the 'iron curtain' may be variable and connected to the accretion. The thesis also explores for the first time the effect a 'warm absorber'would have on the X-ray spectrum and the deduced column densities of high inclination CVs in quiescence. The application of synthetic spectral analyses to ultraviolet observations of CVs is extensively reviewed, with particular emphasis on the spectral components observed. White dwarf model atmospheres and synthetic spectra are generated using TLUSTY and SYNSPEC, and those IUE spectra of cataclysmic variables where the white dwarf can be seen are modelled using a X2 fitting routine. White dwarf synthetic spectra veiled by an 'iron curtain' are also calculated and applied to JUE archive observations of OY Car and similar systems. The resulting independently estimated white dwarf temperatures are compared with published values and with temperatures obtained from the application of different model atmosphere codes. The column density found by Home et al. (1994) is confirmed. IUE archive observations of U Gem show a similar cooling time (~ 30 days) to more recent HST observations. It is shown that the major source of systematic error in estimating the white dwarf temperature from ultraviolet observations is uncertainty in the masses of the white dwarfs. The final Chapter shows how scheduled (simultaneous) HST and ASCA observations of OY Car in quiescence will be used to place further constraints on the temperature of the emitting gas and the column density, and how the techniques developed for the ultraviolet modelling can be applied to the HST data. Future (accepted) XMM observations of UX UMa1, to constrain spectral components in the high mass accretion rate regime, are also discussed

Optical and ROSAT X-ray observations of the dwarf nova OY Carinae in superoutburst and quiescence

We present ROSAT X-ray and optical light curves of the 1994 February superoutburst of the eclipsing SU UMa dwarf nova OY Carinae. There is no eclipse of the flux in the ROSAT HRI light curve. Contemporaneous `wide B' band optical light curves show extensive superhump activity and dips at superhump maximum. Eclipse mapping of these optical light curves reveals a disc with a considerable physical flare, even three days into the superoutburst decline. We include a later (1994 July) ROSAT PSPC observation of OY Car that allows us to put constraints on the quiescent X-ray spectrum. We find that while there is little to choose between OY Car and its fellow high inclination systems with regard to the temperature of the emitting gas and the emission measure, we have difficulties reconciling the column density found from our X-ray observation with the column found in HST UV observations by Horne et al. (1994). The obvious option is to invoke time variability.Comment: 16 pages, 14 figures, accepted for publication in MNRA

The stellar mass function of galaxies in Planck-selected clusters at 0.5 < z < 0.7: new constraints on the timescale and location of satellite quenching

We study the abundance of star-forming and quiescent galaxies in a sample of 21 massive clusters at 0.5<z<0.7, detected with the Planck satellite. We measure the cluster galaxy stellar mass function (SMF), which is a fundamental observable to study and constrain the formation and evolution of galaxies. Our measurements are based on homogeneous and deep multi-band photometry spanning u- to the Ks-band for each cluster and are supported by spectroscopic data from different programs. The galaxy population is separated between quiescent and star-forming galaxies based on their rest-frame U-V and V-J colours. The SMF is compared to that of field galaxies at the same redshifts, using data from the COSMOS/UltraVISTA survey. We find that the shape of the SMF of star-forming galaxies does not depend on environment, while the SMF of quiescent galaxies has a significantly steeper low-mass slope in the clusters compared to the field. We estimate the environmental quenching efficiency (f_EQ), i.e. the probability for a galaxy that would normally be star forming in the field, to be quenched due to its environment. The f_EQ shows no stellar-mass dependence in any environment, but it increases from 40% in the cluster outskirts to ~90% in the cluster centres. The radial signature of f_EQ provides constraints on where the dominant quenching mechanism operates in these clusters and on what timescale. Exploring these using a simple model based on galaxy orbits obtained from an N-body simulation, we find a clear degeneracy between both parameters. For example, the quenching process may either be triggered on a long (~3 Gyr) time scale at large radii (r~8R_500), or happen well within 1 Gyr at r<R_500. The radius where quenching is triggered is at least r_quench> 0.67R_500 (95%CL). The ICM density at this location suggests that ram-pressure stripping of the cold gas is a likely cause of quenching. [Abridged]Comment: 16 pages, 12 figures, accepted for publication in A&

The X-ray Properties of Optically Selected Clusters of Galaxies

We present the results of Chandra and Suzaku X-ray observations of nine moderate-redshift (0.16 < z < 0.42) clusters discovered via the Red-sequence Cluster Survey (RCS). Surface brightness profiles are fitted to beta models, gas masses are determined, integrated spectra are extracted within R2500, and X-ray temperatures and luminosities are inferred. The Lx-Tx relationship expected from self-similar evolution is tested by comparing this sample to our previous X-ray investigation of nine high-redshift (0.6 < z < 1.0) optically selected clusters. We find that optically selected clusters are systematically less luminous than X-ray selected clusters of similar X-ray temperature at both moderate and high-z. We are unable to constrain evolution in the Lx-Tx relation with these data, but find it consistent with no evolution, within relatively large uncertainties. To investigate selection effects, we compare the X-ray properties of our sample to those of clusters in the representative X-ray selected REXCESS sample, also determined within R2500. We find that while RCS cluster X-ray properties span the entire range of those of massive clusters selected by other methods, their average X-ray properties are most similar to those of dynamically disturbed X-ray selected clusters. This similarity suggests that the true cluster distribution might contain a higher fraction of disturbed objects than are typically detected in X-ray selected surveys.Comment: 13 pages, 5 figures; accepted for publication in MNRAS. Figure quality reduced to comply with arXiv file size requirement

Star formation and UV colors of the brightest Cluster Galaxies in the representative XMM-Newton Cluster Structure Survey

We present UV broadband photometry and optical emission-line measurements for a sample of 32 Brightest Cluster Galaxies (BCGs) in clusters of the Representative XMM-Newton Cluster Structure Survey (REXCESS) with z = 0.06-0.18. The REXCESS clusters, chosen to study scaling relations in clusters of galaxies, have X-ray measurements of high quality. The trends of star formation and BCG colors with BCG and host properties can be investigated with this sample. The UV photometry comes from the XMM Optical Monitor, supplemented by existing archival GALEX photometry. We detected H\alpha and forbidden line emission in 7 (22%) of these BCGs, in optical spectra. All of the emission-line BCGs occupy clusters classified as cool cores, for an emission-line incidence rate of 70% for BCGs in cool core clusters. Significant correlations between the H\alpha equivalent widths, excess UV production in the BCG, and the presence of dense, X-ray bright intracluster gas with a short cooling time are seen, including the fact that all of the H\alpha emitters inhabit systems with short central cooling times and high central ICM densities. Estimates of the star formation rates based on H\alpha and UV excesses are consistent with each other in these 7 systems, ranging from 0.1-8 solar masses per year. The incidence of emission-line BCGs in the REXCESS sample is intermediate, somewhat lower than in other X-ray selected samples (-35%), and somewhat higher than but statistically consistent with optically selected, slightly lower redshift BCG samples (-10-15%). The UV-optical colors (UVW1-R-4.7\pm0.3) of REXCESS BCGs without strong optical emission lines are consistent with those predicted from templates and observations of ellipticals dominated by old stellar populations. We see no trend in UV-optical colors with optical luminosity, R-K color, X-ray temperature, redshift, or offset between X-ray centroid and X-ray peak ().Comment: 19 pages, 18 figures, 6 tables. Submitted, with minor revisions, to ApJ