Cold fronts and multi-temperature structures in the core of Abell 2052

The physics of the coolest phases in the hot Intra-Cluster Medium (ICM) of clusters of galaxies is yet to be fully unveiled. X-ray cavities blown by the central Active Galactic Nucleus (AGN) contain enough energy to heat the surrounding gas and stop cooling, but locally blobs or filaments of gas appear to be able to cool to low temperatures of 10^4 K. In X-rays, however, gas with temperatures lower than 0.5 keV is not observed. Using a deep XMM-Newton observation of the cluster of galaxies Abell 2052, we derive 2D maps of the temperature, entropy, and iron abundance in the core region. About 130 kpc South-West of the central galaxy, we discover a discontinuity in the surface brightness of the hot gas which is consistent with a cold front. Interestingly, the iron abundance jumps from ~0.75 to ~0.5 across the front. In a smaller region to the North-West of the central galaxy we find a relatively high contribution of cool 0.5 keV gas, but no X-ray emitting gas is detected below that temperature. However, the region appears to be associated with much cooler H-alpha filaments in the optical waveband. The elliptical shape of the cold front in the SW of the cluster suggests that the front is caused by sloshing of the hot gas in the clusters gravitational potential. This effect is probably an important mechanism to transport metals from the core region to the outer parts of the cluster. The smooth temperature profile across the sharp jump in the metalicity indicates the presence of heat conduction and the lack of mixing across the discontinuity. The cool blob of gas NW of the central galaxy was probably pushed away from the core and squeezed by the adjacent bubble, where it can cool efficiently and relatively undisturbed by the AGN. Shock induced mixing between the two phases may cause the 0.5 keV gas to cool non-radiatively and explain our non-detection of gas below 0.5 keV.Comment: 11 pages, 9 figures, A&A, in pres

The temperature structure in the core of Sersic 159-03

We present results from a new 120 ks XMM-Newton observation of the cluster of galaxies Sersic 159-03. In this paper we focus on the high-resolution X-ray spectra obtained with the Reflection Grating Spectrometer (RGS). The spectra allow us to constrain the temperature structure in the core of the cluster and determine the emission measure distribution as a function of temperature. We also fit the line widths of mainly oxygen and iron lines.Comment: 7 pages and 4 figures. Contribution to the proceedings of the COSPAR Scientific Assembly, session E1.2 "Clusters of Galaxies: New Insights from XMM-Newton, Chandra and INTEGRAL", july 2004, Paris (France). Accepted for publication in Advances in Space Researc

AN XMM-NEWTON SEARCH FOR X-RAY EMISSION FROM THE MICROLENSING EVENT MACHO-96-BLG-5

MACHO-96-BLG-5 was a microlensing event observed toward the bulge of the Galaxy with an exceptionally long duration of ~970 days. The microlensing parallax fit parameters were used to estimate a lens mass M = 6 M☉, corresponding to a distance d in the range 0.5-2 kpc. The upper limit on the absolute brightness for main-sequence stars of the same mass is less than 1 L☉, so the lens is a good black hole candidate. Such a black hole would accrete from the interstellar medium, thereby emitting in the X-ray band. Here we report the analysis of a deep XMM-Newton observation toward the MACHO-96-BLG-5 lens position. Only an upper limit (99.8% confidence level) to the X-ray flux from the lens position, 9.10 × 10-15 to 1.45 × 10-14 ergs cm-2 s-1 in the 0.2-10 keV energy band, is obtained, allowing us to constrain the putative black hole's accretion parameters

The metal contents of two groups of galaxies

The hot gas in clusters and groups of galaxies is continuously being enriched with metals from supernovae and stars. It is well established that the enrichment of the gas with elements from oxygen to iron is mainly caused by supernova explosions. The origins of nitrogen and carbon are still being debated. Possible candidates include massive, metal-rich stars, early generations of massive stars, intermediate or low mass stars and Asymptotic Giant Branch (AGB) stars. In this paper we accurately determine the metal abundances of the gas in the groups of galaxies NGC 5044 and NGC 5813, and discuss the nature of the objects that create these metals. We mainly focus on carbon and nitrogen. We use spatially-resolved high-resolution X-ray spectroscopy from XMM-Newton. For the spectral fitting, multi-temperature hot gas models are used. The abundance ratios of carbon over oxygen and nitrogen over oxygen that we find are high compared to the ratios in the stars in the disk of our Galaxy. The oxygen and nitrogen abundances we derive are similar to what was found in earlier work on other giant ellipticals in comparable environments. We show that the iron abundances in both our sources have a gradient along the cross-dispersion direction of the Reflection Grating Spectrometer (RGS). We conclude that it is unlikely that the creation of nitrogen and carbon takes place in massive stars, which end their lives as core-collapse supernovae, enriching the medium with oxygen because oxygen should then also be enhanced. Therefore we favour low-and intermediate mass stars as sources of these elements. The abundances in the hot gas can best be explained by a 30-40% contribution of type Ia supernovae based on the measured oxygen and iron abundances and under the assumption of a Salpeter Initial Mass Function (IMF).Comment: Accepted for publication in A&A, 12 pages, 10 figures. Data points on which figs 4,5,8 and 9 are based are present as comment in the source fil

X-ray spectral study of the hot gas in three Clusters of Galaxies

We study the physical properties of three clusters of galaxies, selected from a BeppoSAX Wide Field Camera (WFC) survey. These sources are identified as 1RXS J153934.7-833535, 1RXS J160147.6-754507, and 1RXS J081232.3-571423 in the ROSAT All-Sky Survey catalogue. We obtained XMM-Newton follow-up observations for these three clusters. We fit single and multi-temperature models to spectra obtained from the EPIC-pn camera to determine the temperature, the chemical composition of the gas and their radial distribution. Since two observations are contaminated by a high soft-proton background, we develop a new method to estimate the effect of this background on the data. For the first time, we present the temperature and iron abundance of two of these three clusters. The iron abundance of 1RXS J153934.7-33535 decreases with radius. The fits to the XMM-Newton and Chandra data show that the radial temperature profile within 3' towards the centre either flattens or lowers. A Chandra image of the source suggests the presence of X-ray cavities. The gas properties in 1RXS J160147.6-754507 are consistent with a flat radial distribution of iron and temperature within 2' from the centre. 1RXS J081232.3-571423 is a relatively cool cluster with a temperature of about 3 keV. The radial temperature and iron profiles suggest that 1RXS J153934.7-833535 is a cool core cluster. The Chandra image shows substructure which points toward AGN feedback in the core. The flat radial profiles of the temperature and iron abundance in 1RXS J160147.6-754507 are similar to the profiles of non-cool-core clusters.Comment: Accepted for publication in A&A, 8 pages, 8 figures; corrected typos, added data points on which fig 1 and 2 are based as comment to source file

Solving the Cooling Flow Problem through Mechanical AGN Feedback

Unopposed radiative cooling of plasma would lead to the cooling catastrophe, a massive inflow of condensing gas, manifest in the core of galaxies, groups and clusters. The last generation X-ray telescopes, Chandra and XMM, have radically changed our view on baryons, indicating AGN heating as the balancing counterpart of cooling. This work reviews our extensive investigation on self-regulated heating. We argue that the mechanical feedback, based on massive subrelativistic outflows, is the key to solving the cooling flow problem, i.e. dramatically quenching the cooling rates for several Gyr without destroying the cool-core structure. Using a modified version of the 3D hydrocode FLASH, we show that bipolar AGN outflows can further reproduce fundamental observed features, such as buoyant bubbles, weak shocks, metals dredge- up, and turbulence. The latter is an essential ingredient to drive nonlinear thermal instabilities, which cause the formation of extended cold gas, a residual of the quenched cooling flow and, later, fuel for the feedback engine. Compared to clusters, groups and galaxies require a gentler mechanical feedback, in order to avoid catastrophic overheating. We highlight the essential characteristics for a realistic AGN feedback, with emphasis on observational consistency.Comment: Accepted by AN; 4 pages, 2 figure

Abundance and temperature distributions in the hot intra-cluster gas of Abell 4059

Using the EPIC and RGS data from a deep (~200 ks) XMM-Newton observation, we investigate the temperature structure (kT and sigma_T ) and the abundances of 9 elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) of the intra-cluster medium (ICM) in the nearby (z=0.046) cool-core galaxy cluster Abell 4059. Next to a deep analysis of the cluster core, a careful modelling of the EPIC background allows us to build radial profiles up to 12' (~650 kpc) from the core. Probably because of projection effects, the temperature ICM is found not to be in single phase, even in the outer parts of the cluster. The abundances of Ne, Si, S, Ar, Ca and Fe, but also O are peaked towards the core. Fe and O are still significantly detected in the outermost annuli; suggesting that the enrichment by both type Ia and core-collapse SNe started in the early stages of the cluster formation. However, the particularly high Ca/Fe ratio that we find in the core is not well reproduced by the standard SNe yield models. Finally, 2-D maps of temperature and Fe abundance are presented and confirm the existence of a denser, colder, and Fe-rich ridge southwest of the core, previously observed by Chandra. The origin of this asymmetry in the hot gas of the cluster core is still unclear, but might be explained by a past intense ram-pressure stripping event near the central cD galaxy.Comment: 17 pages, 13 figures, accepted for publication in A&