LoCuSS:the connection between brightest cluster galaxy activity, gas cooling and dynamical disturbance of X-ray cluster cores

We study the distribution of projected offsets between the cluster X-ray centroid and the brightest cluster galaxy (BCG) for 65 X-ray-selected clusters from the Local Cluster Substructure Survey, with a median redshift of z= 0.23. We find a clear correlation between X-ray/BCG projected offset and the logarithmic slope of the cluster gas density profile at 0.04r500(α), implying that more dynamically disturbed clusters have weaker cool cores. Furthermore, there is a close correspondence between the activity of the BCG, in terms of detected Hα and radio emission, and the X-ray/BCG offset, with the line-emitting galaxies all residing in clusters with X-ray/BCG offsets of ≤15 kpc. Of the BCGs with α < −0.85 and an offset <0.02r500, 96 per cent (23/24) have optical emission and 88 per cent (21/24) are radio active, while none has optical emission outside these criteria. We also study the cluster gas fraction (fgas) within r500 and find a significant correlation with X-ray/BCG projected offset. The mean fgas of the ‘small offset’ clusters (<0.02r500) is 0.106 ± 0.005 (σ= 0.03) compared to 0.145 ± 0.009 (σ= 0.04) for those with an offset >0.02r500, indicating that the total mass may be systematically underestimated in clusters with larger X-ray/BCG offsets. Our results imply a link between cool core strength and cluster dynamical state consistent with the view that cluster mergers can significantly perturb cool cores, and set new constraints on models of the evolution of the intracluster medium

Visualization techniques and graphical user interfaces in syndromic surveillance systems. Summary from the Disease Surveillance Workshop, Sept. 11–12, 2007; Bangkok, Thailand

Timeliness is a critical asset to the detection of public health threats when using syndromic surveillance systems. In order for epidemiologists to effectively distinguish which events are indicative of a true outbreak, the ability to utilize specific data streams from generalized data summaries is necessary. Taking advantage of graphical user interfaces and visualization capacities of current surveillance systems makes it easier for users to investigate detected anomalies by generating custom graphs, maps, plots, and temporal-spatial analysis of specific syndromes or data sources

Seeking help for perinatal psychological distress: a meta-synthesis of women's experiences

Background Women may not seek help for perinatal psychological distress, despite regular contact with primary care services. Barriers include ignorance of symptoms, inability to disclose distress, others’ attitudes, and cultural expectations. Much of the evidence has been obtained from North American populations and may not, therefore, extrapolate to the UK. Aim To understand the factors affecting women’s decision to seek help for perinatal distress. Design and setting Meta-synthesis of the available published qualitative evidence on UK women’s experiences of seeking help for perinatal distress. Method Systematic searches were conducted in accordance with PRISMA guidelines. Databases searched were PubMed, Scopus, PsycINFO, PsycARTICLES, CINAHL, and Academic Search Complete. Searches of grey literature and references were also conducted. Studies were eligible for inclusion if they reported qualitative data on UK women’s experiences of perinatal distress and contact with healthcare professionals. The synthesis was conducted using meta-ethnography. Results In all, 24 studies were eligible for inclusion. Metasynthesis identified three main themes: identifying a problem, the influence of healthcare professionals, and stigma. These themes build on current understanding of help seeking by identifying the need for women to be able to frame their experience, for healthcare professionals to educate women about their roles, the need for continuity of care, and the way that being seen as a ‘bad mother’ causes women to self-silence. Conclusion Perinatal care provision needs to allow for continuity of care and for staff training that facilitates awareness of factors that influence women’s help seeking. Further research is required, particularly in relation to effective means of identifying perinatal psychological distress

Sound waves in the intracluster medium of the Centaurus cluster

We report the discovery of ripple-like X-ray surface brightness oscillations in the core of the Centaurus cluster of galaxies, found with 200 ks of Chandra observations. The features are between 3 to 5 per cent variations in surface brightness with a wavelength of around 9 kpc. If, as has been conjectured for the Perseus cluster, these are sound waves generated by the repetitive inflation of central radio bubbles, they represent around 5x10^42 erg/s of spherical sound-wave power at a radius of 30 kpc. The period of the waves would be 10^7 yr. If their power is dissipated in the core of the cluster, it would balance much of the radiative cooling by X-ray emission, which is around 1.3x10^43 erg/s within the inner 30 kpc. The power of the sound waves would be a factor of four smaller that the heating power of the central radio bubbles, which means that energy is converted into sound waves efficiently.Comment: 5 page letter, 5 figures, accepted by MNRA

Chandra and XMM-Newton X-ray observations of AWM 7 - I: Investigating X-ray surface brightness fluctuations

We investigate the levels of small scale structure in surface brightness images of the core of the X-ray bright cool-core galaxy cluster AWM 7. After subtraction of a model of the smooth cluster emission, we find a number of approximately radial surface brightness depressions which are not present in simulated images and are seen in both the Chandra and XMM-Newton data. The depressions are most strongly seen in the south of the cluster and have a magnitude of around 4 per cent in surface brightness. We see these features in both an energy band sensitive to the density (0.6 to 5 keV) and a band more sensitive to the pressure (3.5 to 7.5 keV). Histograms of surface brightness in the data, when compared to realisations of a smooth model, reveal stronger surface brightness variations. We use the Delta-variance technique to characterise the magnitude of the fluctuations as a function of length scale. We find that the spectrum in the 0.6 to 5 keV band is flatter than expected for Kolmogorov index fluctuations. If characterised by a power spectrum, on large scales it would have an index around -1.7, rather than -3.7. The implied 3D density fluctuations have a standard deviation of around 4 per cent. The implied 3D pressure variations are at most 4 per cent. Most of the longer-scale power in the density spectrum is contributed by the southern half of the cluster, where the depressions are seen. The density variations implied by the spectrum of the northern sector have a standard deviation of about 2 per cent.Comment: 17 pages, accepted by MNRAS, high resolution version available at http://www-xray.ast.cam.ac.uk/papers/awm7.pd

LoCuSS: Connecting the Dominance and Shape of Brightest Cluster Galaxies with the Assembly History of Massive Clusters

We study the luminosity gap, dm12, between the first and second ranked galaxies in a sample of 59 massive galaxy clusters, using data from the Hale Telescope, HST, Chandra, and Spitzer. We find that the dm12 distribution, p(dm12), is a declining function of dm12, to which we fitted a straight line: p(dm12) propto -(0.13+/-0.02)dm12. The fraction of clusters with "large" luminosity gaps is p(dm12>=1)=0.37+/-0.08, which represents a 3sigma excess over that obtained from Monte Carlo simulations of a Schechter function that matches the mean cluster galaxy luminosity function. We also identify four clusters with "extreme" luminosity gaps, dm12>=2, giving a fraction of p(dm12>=2)=0.07+0.05-0.03. More generally, large luminosity gap clusters are relatively homogeneous, with elliptical/disky brightest cluster galaxies (BCGs), cuspy gas density profiles (i.e. strong cool cores), high concentrations, and low substructure fractions. In contrast, small luminosity gap clusters are heterogeneous, spanning the full range of boxy/elliptical/disky BCG morphologies, the full range of cool core strengths and dark matter concentrations, and have large substructure fractions. Taken together, these results imply that the amplitude of the luminosity gap is a function of both the formation epoch, and the recent infall history of the cluster. "BCG dominance" is therefore a phase that a cluster may evolve through, and is not an evolutionary "cul-de-sac". We also compare our results with semi-analytic model predictions based on the Millennium Simulation. None of the models are able to reproduce all of the observational results, underlining the inability of current models to match the empirical properties of BCGs. We identify the strength of AGN feedback and the efficiency with which cluster galaxies are replenished after they merge with the BCG in each model as possible causes of these discrepancies. [Abridged]Comment: 15 pages, 12 figures, accepted for publication in MNRA

Are luminous radio-loud active galactic nuclei triggered by galaxy interactions?

We present the results of a comparison between the optical morphologies of a complete sample of 46 southern 2Jy radio galaxies at intermediate redshifts (0.05<z<0.7) and those of two control samples of quiescent early-type galaxies: 55 ellipticals at redshifts z<0.01 from the Observations of Bright Ellipticals at Yale (OBEY) survey, and 107 early-type galaxies at redshifts 0.2<z<0.7 in the Extended Groth Strip (EGS). Based on these comparisons, we discuss the role of galaxy interactions in the triggering of powerful radio galaxies (PRGs). We find that a significant fraction of quiescent ellipticals at low and intermediate redshifts show evidence for disturbed morphologies at relatively high surface brightness levels, which are likely the result of past or on-going galaxy interactions. However, the morphological features detected in the galaxy hosts of the PRGs (e.g. tidal tails, shells, bridges, etc.) are up to 2 magnitudes brighter than those present in their quiescent counterparts. Indeed, if we consider the same surface brightness limits, the fraction of disturbed morphologies is considerably smaller in the quiescent population (53% at z<0.2 and 48% at 0.2<z<0.7) than in the PRGs (93% at z<0.2 and 95% at 0.2<z<0.7 considering strong-line radio galaxies only). This supports a scenario in which PRGs represent a fleeting active phase of a subset of the elliptical galaxies that have recently undergone mergers/interactions. However, we demonstrate that only a small proportion (<20%) of disturbed early-type galaxies are capable of hosting powerful radio sources.Comment: 20 pages, 7 figures, accepted for publication in MNRA

AGN feedback and iron enrichment in the powerful radio galaxy, 4C+55.16

We present a detailed X-ray analysis of 4C+55.16, an unusual and interesting radio galaxy, located at the centre of a cool core cluster of galaxies. 4C+55.16 is X-ray bright (L(cluster)~10^45 erg/s), radio powerful, and shows clear signs of interaction with the surrounding intracluster medium. By combining deep Chandra (100 ks) with 1.4 GHz VLA observations, we find evidence of multiple outbursts from the central AGN, providing enough energy to offset cooling of the ICM (P_bubbles=6.7x10^44 erg/s). Furthermore, 4C+55.16 has an unusual intracluster iron distribution showing a plume-like feature rich in Fe L emission that runs along one of the X-ray cavities. The excess of iron associated with the plume is around 10^7M_sol. The metal abundances are consistent with being Solar-like, indicating that both SNIa and SNII contribute to the enrichment. The plume and southern cavity form a region of cool metal-rich gas, and at the edge of this region, there is a clear discontinuity in temperature (from kT~2.5 keV to kT~5.0 keV), metallicity (from ~0.4 solar to 0.8 solar), and surface brightness distribution, consistent with it being caused by a cold front. However, we also suggest that this discontinuity could be caused by cool metal-rich gas being uplifted from the central AGN along one of its X-ray cavities.Comment: 12 pages, 11 figures, 1 table, Accepted to MNRAS (minor revision

Galaxy and Mass Assembly (GAMA): the wavelength dependence of galaxy structure versus redshift and luminosity

We study how the sizes and radial profiles of galaxies vary with wavelength, by fitting Se´rsic functions simultaneously to imaging in nine optical and near-infrared bands. To quantify the wavelength dependence of effective radius we use the ratio, R, of measurements in two rest- frame bands. The dependence of Se´rsic index on wavelength, N , is computed correspondingly. Vulcani et al. have demonstrated that different galaxy populations present sharply contrasting behaviour in terms of R and N . Here we study the luminosity dependence of this result. We find that at higher luminosities, early-type galaxies display a more substantial decrease in effective radius with wavelength, whereas late types present a more pronounced increase in Se´rsic index. The structural contrast between types thus increases with luminosity. By considering samples at different redshifts, we demonstrate that lower data quality reduces the apparent difference between the main galaxy populations. However, our conclusions remain robust to this effect. We show that accounting for different redshift and luminosity selections partly reconciles the size variation measured by Vulcani et al. with the weaker trends found by other recent studies. Dividing galaxies by visual morphology confirms the behaviour inferred using morphological proxies, although the sample size is greatly reduced. Finally, we demonstrate that varying dust opacity and disc inclination can account for features of the joint distribution of R and N for late-type galaxies. However, dust does not appear to explain the highest values of R and N . The bulge–disc nature of galaxies must also contribute to the wavelength dependence of their structure. Key words: galaxies: formation – galaxies: fundamental parameters – galaxies: general – galaxies: structure