A Catalog of Galaxy Clusters Observed by XMM-Newton

Aims: We present a uniform catalog of the images and radial profiles of the temperature, abundance, and brightness for 70 clusters of galaxies observed by XMM-Newton. Methods: We use a new "first principles" approach to the modeling and removal of the background components; the quiescent particle background, the cosmic diffuse emission, the soft proton contamination, and the solar wind charge exchange emission. Each of the background components demonstrate significant spectral variability, several have spatial distributions that are not described by the photon vignetting function, and all except for the cosmic diffuse emission are temporally variable. Because these backgrounds strongly affect the analysis of low surface brightness objects, we provide a detailed description our methods of identification, characterization, and removal. Results: We have applied these methods to a large collection of XMM-Newton observations of clusters of galaxies and present the resulting catalog. We find significant systematic differences between the Chandra and XMM-Newton temperatures.Comment: Accepted for publication in A&A, 55 pages with 42 figure

Groups and the Entropy Floor- XMM-Newton Observations of Two Groups

Using XMM-Newton spatially resolved X-ray imaging spectroscopy we obtain the temperature, density, entropy, gas mass, and total mass profiles for two groups of galaxies out to ~0.3 Rvir (Rvir, the virial radius). Our density profiles agree well with those derived previously, and the temperature data are broadly consistent with previous results but are considerably more precise. Both of these groups are at the mass scale of 2x10^13 Msolar but have rather different properties. They have considerably lower gas mass fractions at r<0.3 Rvir than the rich clusters. NGC2563, one of the least luminous groups for its X-ray temperature, has a very low gas mass fraction of ~0.004 inside 0.1 Rvir, which rises with radius. NGC4325, one of the most luminous groups at the same average temperature, has a higher gas mass fraction of 0.02. The entropy profiles and the absolute values of the entropy as a function of virial radius also differ, with NGC4325 having a value of ~100 keV cm-2 and NGC2563 a value of ~300 keV cm-2 at r~0.1 Rvir. For both groups the profiles rise monotonically with radius and there is no sign of an entropy "floor". These results are inconsistent with pre-heating scenarios which have been developed to explain the entropy floor in groups but are broadly consistent with models of structure formation which include the effects of heating and/or the cooling of the gas. The total entropy in these systems provides a strong constraint on all models of galaxy and group formation, and on the poorly defined feedback process which controls the transformation of gas into stars and thus the formation of structure in the universe.Comment: 22 pages, 2 figure

X-ray observations of PKS 0745-191 at the virial radius: Are we there yet?

We wish to reassess the properties of the ICM at large radii in the galaxy cluster PKS 0745-191 in light of the recent Suzaku measurements. We analyze an archival 10.5 ksec ROSAT/PSPC observation to extract the surface-brightness profile of PKS 0745-191 and infer the deprojected density profile. We then compare the ROSAT surface-brightness profile with the Suzaku result. We perform a mass analysis combining the ROSAT density profile and the published temperature profiles from different instruments. We find that the ROSAT surface-brightness profile is statistically inconsistent (7.7 sigma) with the Suzaku result around and beyond the value of r200 estimated by Suzaku. We argue that, thanks to its large field of view and low background, ROSAT/PSPC is to the present day the most sensitive instrument to low surface-brightness X-ray emission in the 0.4-2.0 keV band. We also note that the Suzaku temperature and mass profiles are at odds with the results from at least two other satellites (XMM-Newton and Swift). The difference in surface brightness between ROSAT and Suzaku is most likely explained by the existence of additional foreground components at the low Galactic latitude of the source, which were not taken into account in the Suzaku background modeling. In light of our mass analysis, we conclude that any estimate of the fraction of the virial radius reached by X-ray measures is affected by systematic errors of the order of 25%. As a result, the properties of the ICM at the virial radius are still uncertain, and the Suzaku results should be considered with caution.Comment: 6 pages, 5 figures, accepted for publication in A&

The EPIC-MOS Particle-Induced Background Spectrum

We have developed a method for constructing a spectrum of the particle-induced instrumental background of the XMM-Newton EPIC MOS detectors that can be used for observations of the diffuse background and extended sources that fill a significant fraction of the instrument field of view. The strength and spectrum of the particle-induced background, that is, the background due to the interaction of particles with the detector and the detector surroundings, is temporally variable as well as spatially variable over individual chips. Our method uses a combination of the filter-wheel-closed data and a database of unexposed-region data to construct a spectrum of the "quiescent" background. We show that, using this method of background subtraction, the differences between independent observations of the same region of "blank sky" are consistent with the statistical uncertainties except when there is clear evidence of solar wind charge exchange emission. We use the blank sky observations to show that contamination by SWCX emission is a strong function of the solar wind proton flux, and that observations through the flanks of the magnetosheath appear to be contaminated only at much higher solar wind fluxes. We have also developed a spectral model of the residual soft proton flares, which allows their effects to be removed to a substantial degree during spectral fitting

The Chandra M10l Megasecond: Diffuse Emission

Because MIOl is nearly face-on, it provides an excellent laboratory in which to study the distribution of X-ray emitting gas in a typical late-type spiral galaxy. We obtained a Chandra observation with a cumulative exposure of roughly 1 Ms to study the diffuse X-ray emission in MlOl. The bulk of the X-ray emission is correlated with the star formation traced by the FUV emission. The global FUV/Xray correlation is non-linear (the X-ray surface brightness is roughly proportional to the square root of the FUV surface brightness) and the small-scale correlation is poor, probably due to the delay between the FUV emission and the X-ray production ill star-forming regions. The X-ray emission contains only minor contributions from unresolved stars (approximates less than 3%), unresolved X-ray point sources (approximates less than 4%), and individual supernova remnants (approximates 3%). The global spectrum of the diffuse emission can be reasonably well fitted with a three component thermal model, but the fitted temperatures are not unique; many distributions of emission measure can produce the same temperatures when observed with the current CCD energy resolution. The spectrum of the diffuse emission depends on the environment; regions with higher X-ray surface brightnesses have relatively stronger hard components, but there is no significant evidence that the temperatures of the emitting components increase with surface brightness

An X-ray Survey of Galaxies in Pairs

Results are reported from the first survey of X-ray emission from galaxies in pairs. The sample consists of fifty-two pairs of galaxies from the Catalog of Paired Galaxies Karachentsev (1972) whose coordinates overlap ROSAT Position Sensitive Proportional Counter pointed observations. The mean observed log l_x for early-type pairs is 41.35 +/-0.21 while the mean log l_x predicted using the l_x-l_b relationship for isolated early-type galaxies is 42.10 +/-0.19. With 95% confidence, the galaxies in pairs are underluminous in the X-ray, compared to isolated galaxies, for the same l_b. A significant fraction of the mixed pair sample also appear similarly underluminous. A spatial analysis shows that the X-ray emission from pairs of both types typically has an extent of ~10 - 50 kpc, much smaller than group intergalactic medium and thus likely originates from the galaxies. CPG 564, the most X-ray luminous early-type pair, 4.7x10^42 ergs/sec, is an exception. The extent of it's X-ray emission, >169 kpc, and HWHM, ~80 kpc, is comparable to that expected from an intergalactic medium. The sample shows only a weak correlation, ~81% confidence, between l_x and l_b, presumably due to variations in gas content within the galaxies. No correlation between l_x and the pair velocity difference, separation, or far-infrared luminosity is found though the detection rate is low, 22%.Comment: 40 pages, 6 jpg figures, ApJ (in press

HEA Flexible Learning Practice Guide

This Guide is designed to help practitioners develop flexible learning processes across a range of domains and levels and to aid subsequent implementation. It starts by providing practitioners with some contested definitions of flexible learning and argues a case for a particular approach; it articulates a set of overarching principles for flexible learning processes; covers the parameters of flexible learning and outlines what falls outside of scope; it considers the implications for staff and institutions when operationalising flexible learning processes and possible impact on students; finally, it provides brief synopses of others' innovative approaches in this domain alongside further resources. The immediate intention is to build confidence in those seeking to use more inclusive, collaborative and flexible pedagogical processes in enhancing student success. A longer-term ambition is to develop an emerging network of practitioners as part of our Flexible Learning Community of Practice who can use this Guide as a conduit for sharing further ideas and to use as a springboard for taking flexible learning to a new level. The Guide should be read in conjunction with the illustrative case studies and with the HEA Framework for Flexible Learning in higher education (2015) against which many of its key principles are aligned

Local ISM 3D Distribution and Soft X-ray Background Inferences for Nearby Hot Gas

Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and are filled by hot gas. To demonstrate this, and to derive a clearer picture of the local ISM, we compare our recent 3D IS dust distribution maps to the ROSAT diffuse Xray background maps after removal of heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred mean pressure in the local cavities is found to be approx.9,400/cu cm K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in those regions, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas and as a consequence a reduction of the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy (0.75 keV) enhancements in the fourth and first quadrants. Tunnels and cavities are found to coincide with the main bright areas, however no tunnel nor cavity is found to match the low-latitude b > or approx. 8deg, brightest part of the NPS. In addition, the comparison between the 3D maps and published spectral data favors a NPS central source region location beyond 230 pc, i.e. at larger distance than usually considered. Those examples illustrate the potential use of more detailed 3D distributions of the nearby ISM for the interpretation of the diffuse soft X-ray background

X-ray observations of the galaxy cluster Abell 2029 to the virial radius

We present Suzaku observations of the galaxy cluster Abell 2029, which exploit Suzaku's low particle background to probe the ICM to radii beyond those possible with previous observations (reaching out to the virial radius), and with better azimuthal coverage. We find significant anisotropies in the temperature and entropy profiles, with a region of lower temperature and entropy occurring to the south east, possibly the result of accretion activity in this direction. Away from this cold feature, the thermodynamic properties are consistent with an entropy profile which rises, but less steeply than the predictions of purely gravitational hierarchical structure formation. Excess emission in the northern direction can be explained due to the overlap of the emission from the outskirts of Abell 2029 and nearby Abell 2033 (which is at slightly higher redshift). These observations suggest that the assumptions of spherical symmetry and hydrostatic equilibrium break down in the outskirts of galaxy clusters, which poses challenges for modelling cluster masses at large radii and presents opportunities for studying the formation and accretion history of clusters.Comment: 15 pages, 14 figures. Accepted for publication in the Monthly Notices of the Royal Astronomical Societ