Jonathan P. D. Mittaz

Diffuse Extreme-Ultraviolet Emission from the Coma Cluster: Evidence for Rapidly Cooling Gases at Submegakelvin Temperatures

The central region of the Coma cluster of galaxies was observed in the energy band from 0.065 to 0.245 kiloelectron volts by the Deep Survey telescope aboard the Extreme Ultraviolet Explorer. A diffuse emission halo of angular diameter ∼30 arc minutes was detected. The extreme-ultraviolet (EUV) emission level exceeds that expected from the x-ray temperature gas in Coma. This halo suggests the presence of two more phases in the emitting gas, one at a temperature of ∼2 × 106 kelvin and the other at ∼8 × 105 kelvin. The latter phase cools rapidly and, in steady state, would have produced cold matter with a mass of ∼1014 solar masses within the EUV halo. Although a similar EUV enhancement was discovered in the Virgo cluster, this detection in Coma applies to a noncooling flow system.

THERMAL AND NONTHERMAL NATURE OF THE SOFT EXCESS EMISSION FROM SERSIC 159-03 OBSERVED WITH XMM-NEWTON

Several nearby clusters exhibit an excess of soft X-ray radiation that cannot be attributed to the hot virialized intracluster medium. There is no consensus to date on the origin of the excess emission: it could be either of thermal origin or due to an inverse Compton scattering of the cosmic microwave background. Using high-resolution XMM-Newton data of Sersic 159-03 we first show that strong soft excess emission is detected out to a radial distance of 0.9 Mpc. The data are interpreted using the two viable models available, i.e., by invoking either a warm reservoir of thermal gas or relativistic electrons that are part of a cosmic-ray population. The thermal interpretation of the excess emission, slightly favored by the goodness-of-fit analysis, indicates that the warm gas responsible for the emission is high in mass and low in metallicity.

Soft x-ray emission from clusters of galaxies and related phenomena

Contributing authors Preface Part I The Cluster soft excess The extreme ultraviolet excess emission in five clusters of galaxies revisited Florence Durret, Eric Slezak, Richard Lieu, Sergio Dos Santos, Massimiliano Bonamente Soft (1 keV) X-ray emission in Galaxy clusters Mark Henriksen A massive halo of warm baryons in the Coma cluster M. Bonamente, M.K. Joy and R. Lieu Soft X-ray excess emission in three clusters of galaxies observed with XMM-Newton J. Nevailanen, R. Lieu, M. Bonamente, D. Lumb XMM-Newton discovery of O VII emission from warm gas in clusters of galaxies Jelle S. Kaastra, R. Lieu, T. Tamura, F.B.S. Paerels and J.W.A. den Herder XMM-Newton discovery of an X-ray filament in Coma A. Finoguenov, U.G. Briel and. J.P. Henry The cluster Abell 85 and its X-ray filament revisited by Chandra and XMM-Newton. Florence Durret, Gastao B. Lima Neto, William R. Forman, Eugene Churazov Part II Absorption line studies of out Galaxy and the WHIM Chandra detection of X-ray absorption from local warm/hot gas T. Fang, C. Canizares, K. Sembach, H. Marshall, J. Lee, D. Davis The FUSE survey of O VI in the galactic halo B.D. Savage, K.R. Sembach, B.P. Wakker, P. Richter, M. Meade, E.B. Jenkins, J.M. Shull, H.W. Moos, G. Sonneborn The FUSE survey of high velocity O VI in the vicinity of the Milky Way K.R. Sembach, B.P. Wakker, B.D. Savage, P. Richter, M. Meade, J.M. Shull, E.B. Jenkins, H.W. Moos, G. Sonneborn Ionization of high velocity clouds in the Galactic halo Jonathan D. Slavin Part III Soft X-ray data analysis issues The ISM from the soft X-ray background perspective S.L. Snowden Peering through the muck: the influence of the ISM on observations Felix J. Lockman Part IV Hard X-ray excesses and non-thermal processes Hard X-ray excesses in clusters of galaxies and their non-thermal origin R. Fusco-Femiano Thermal and non-thermal SZ Effect in Galaxy Clusters S. Colafrancesco What the SZ Effect can tell us about the electron population in the Coma Cluster? S. Colafrancesco Part V Theoretical models of clusters, the CSE and the WHIM Observational constraints on models for the clusters soft excess emission Richard Lieu and Jonathan P.D. Mittaz High resolution simulations of clusters of galaxies Daisuke Nagai, Andrey V. Kravtsov WHIM emission and the cluster soft excess: a model comparison Jonathan P.D. Mittaz, Richard Lieu and Renyue Cen Part VI New instrumentation and the future Observing the warm-hot intergalactic medium with XEUS Jelle S. Kaastra and Frits B.S. Paerels

Warm-hot Intergalactic Medium Emission and the Cluster Soft Excess: A Model Comparison

The confirmation of the cluster soft excess (CSE) by XMM-Newton has rekindled interest as to its origin. The recent detections of CSE emission at large cluster radii together with reports of O VII line emission associated with the CSE has led many authors to conjecture that the CSE is, in fact, a signature of the warm-hot intergalactic medium (WHIM). In this paper we test the scenario by comparing the observed properties of the CSE with predictions based on models of the WHIM. We find that emission from the WHIM in current models is 3-4 orders of magnitude too faint to explain the CSE. We discuss different possibilities for this discrepancy, including issues of simulation resolution and scale and the role of small density enhancements or galaxy groups. Our final conclusion is that it is unlikely that the WHIM alone is able to account for the observed flux of the CSE.

On the Absence of Gravitational Lensing of the Cosmic Microwave Background

The magnification of distant sources by mass clumps at lower (z ≤ 1) redshifts is calculated analytically. The clumps are initially assumed to be galaxy group isothermal spheres with properties inferred from an extensive survey. The average effect, which includes strong lensing, is exactly counteracted by the beam divergence in between clumps (more precisely, the average reciprocal magnification cancels the inverse Dyer-Roeder demagnification). This conclusion is independent of the matter density function within each clump, and remains valid for arbitrary values of Ωm and ΩΛ. When tested against the cosmic microwave background data, a rather large lensing-induced dispersion in the angular size of the primary acoustic peaks of the temperature-temperature (TT) power spectrum is inconsistent with WMAP observations. The situation is unchanged by the use of Navarro-Frenk-White (NFW) profiles for the density distribution of groups, which lead in fact to slightly larger fluctuations. Finally, our formulae are applied to an ensemble of NFW mass clumps or isothermal spheres having the properties of galaxy clusters. The acoustic peak size dispersion remains unobservably large and is also excluded by WMAP. For galaxy groups, two possible ways of reconciling with the data are proposed, both exploiting maximally the uncertainties in our knowledge of group properties. The same escape routes are not available in the case of clusters, however, because their properties are well understood. Here we have a more robust conclusion: neither the NFW nor isothermal sphere profiles are accurate descriptions of clusters, or important elements of physics responsible for shaping zero-curvature space are missing from the standard cosmological model. When all the effects are accrued, it is difficult to understand how WMAP could reveal no evidence whatsoever of lensing by groups and clusters.

THE CLUSTER SOFT EXCESS: NEW FACES OF AN OLD ENIGMA

Until the advent of XMM-Newton, the cluster soft excess (CSE) was the subject of some controversy due to both data analysis issues and uncertainties with the soft excess emission mechanism. XMM-Newton observations have finally laid to rest any doubts as to the existence of the CSE and have also given tantalising clues as to the nature of its emission mechanism. Here we report on the analysis of XMM-Newton observations of a number of CSE clusters in an attempt to improve the analysis and understanding of the CSE. Included as part of the study is an analysis of the effects of background subtraction, which calls to question the integrity of the claimed O VII line discovery, though not the soft excess itself. We also give details of both thermal and non-thermal fits to the CSE cluster Abell 3112.

Observational Constraints on Models for the Cluster Soft Excess Emission

Although the cluster soft excess phenomenon is confirmed by XMM-Newton observations of many clusters, the cause of this new component of radiation remains an enigma. The two mechanisms proposed in the late 90’s, viz. thermal emission from a massive warm baryonic gas and inverse-Compton scattering between cosmic rays and the microwave background, are still to date the only viable interpretations of the soft excess. In as much as cosmic rays cannot exist at the vast void of a cluster’s outskirts, warm gas also cannot be present with any significant degree of abundance at the center of a cluster. In this sense, one could say that both models have their merits, and account for the soft excess in different spatial regions. There is however no clincher evidence that points definitively to the correctness of either explanation. Thus the door remains open for more exotic scenarios that could even consider the detected emission as signature of some dark matter process. In fact, the absence of absorption lines in the spectrum of background quasars along sightlines going through the outer radii of clusters argues against the thermal model within the domain where it most suitably applies. On the other hand, if the central excesses are due to cosmic rays, the pressure of the proton component will be large enough to choke a cooling flow, and missions like GLAST may have the sensitivity to detect the gamma rays that ensue from proton-gas interactions. However the diagnosis may turn out to be, it is likely that the new radiation represents something of cosmological importance.

Whim Emission and the Cluster Soft Excess: A Model Comparison

The confirmation of the cluster soft excess (CSE) by XMM-Newton has rekindled interest as to its origin. The recent detections of CSE emission at large cluster radii together with reports of OVII line emission associated with the CSE has led many authors to conjecture that the CSE is, in fact, a signature of the warm-hot intergalactic medium (WHIM). In this paper we test this scenario by comparing the observed properties of the CSE with predictions based on models of the WHIM. We find that emission from the WHIM is 3 to 4 orders of magnitude too faint to explain the CSE emission. The only possibility is the models if they are missing a large population of small density enhancements or galaxy groups, but this would place have severe ramifications on the baryon budget.