Metallicity structure in X-ray bright galaxy groups

Using Chandra X-ray data of a sample of 15 X-ray bright galaxy groups, we present preliminary results of a coherent study of the radial distribution of metal abundances in the hot gas in groups. The iron content in group outskirts is found to be lower than in clusters by a factor of ~2, despite showing mean levels in the central regions comparable to those of clusters. The abundance profiles are used to constrain the contribution from supernovae type Ia and II to the chemical enrichment and thermal energy of the intragroup medium at different group radii. The results suggest a scenario in which a substantial fraction of the chemical enrichment of groups took place in filaments prior to group collapse.Comment: 5 pages, 2 figures. To appear in the proceedings of ESO Astrophysics Symposia: "Groups of Galaxies in the Nearby Universe", eds. I. Saviane, V. Ivanov, J. Burissova (Springer

XMM-Newton Witness of M86 X-ray Metamorphosis

The environmental influence of cluster media on its member galaxies, known as Butcher--Oemler effect, has recently been subject to revision due to numerous observations of strong morphological transformations occurring outside the cluster virial radii, caused by some unidentified gas removal processes. In this context we present new XMM-Newton observations of M86 group. The unique combination of high spatial and spectral resolution and large field of view of XMM-Newton allows an in-depth investigation of the processes involved in the spectacular disruption of this object. We identify a possible shock with Mach number of ~1.4 in the process of crushing the galaxy in the North-East direction. The latter is ascribed to the presence of a dense X-ray emitting filament, previously revealed in the RASS data. The shock is not associated with other previously identified features of M86 X-ray emission, such as the plume, the north-eastern arm and the southern extension, which are found to have low entropy, similar to the inner 2 kpc of M86. Finally, mere existence of the large scale gas halo around the M86 group, suggests that the disruptions of M86's X-ray halo may be caused by small-scale types of interactions such as galaxy-galaxy collisions.Comment: 11 pages, A&A in pres

Details of the mass--temperature relation for clusters of galaxies

We present results on the total mass and temperature determination using two samples of clusters of galaxies. One sample is constructed with emphasis on the completeness of the sample, while the advantage of the other is the use of the temperature profiles, derived with ASCA. We obtain remarkably similar fits to the M-T relation for both samples, with the normalization and the slope significantly different from both prediction of self-similar collapse and hydrodynamical simulations. We discuss the origin of these discrepancies and also combine the X-ray mass with velocity dispersion measurements to provide a comparison with high-resolution dark matter simulations. Finally, we discuss the importance of a cluster formation epoch in the observed M-T relation.Comment: 12 pages, A&A 2001 in pres

The Birmingham-CfA cluster scaling project - III: entropy and similarity in galaxy systems

We examine profiles and scaling properties of the entropy of the intergalactic gas in a sample of 66 virialized systems, ranging in mass from single elliptical galaxies to rich clusters, for which we have resolved X-ray temperature profiles. Some of the properties we derive appear to be inconsistent with any of the models put forward to explain the breaking of self-similarity in the baryon content of clusters. In particular, the entropy profiles, scaled to the virial radius, are broadly similar in form across the sample, apart from a normalization factor which differs from the simple self-similar scaling with temperature. Low mass systems do not show the large isentropic cores predicted by preheating models, and the high entropy excesses reported at large radii in groups by Finoguenov et al (2002) are confirmed, and found to extend even to moderately rich clusters. We discuss the implications of these results for the evolutionary history of the hot gas in clusters, and suggest that preheating may affect the entropy of intracluster gas primarily by reducing the density of material accreting into groups and clusters along cosmic filaments.Comment: 13 pages, 8 figures - accepted for publication in MNRA

Chandra Observation of M84, Radio Lobe Elliptical in Virgo cluster

We analyzed a deep Chandra observation of M84, a bright elliptical galaxy in the core of the Virgo cluster. We find that the spatial distribution of the soft X-ray emission is defined by the radio structure of the galaxy. In particular we find two low density regions associated with the radio lobes and surrounded by higher density X-ray filaments. In addition to a central AGN and a population of galactic sources, we find a diffuse hard source filling the central 10 kpc region. Since the morphology of the hard source appears round and is different from that seen in the radio or in soft X-rays, we propose that it is hot gas heated by the central AGN. Finally, we find that the central elemental abundance in the X-ray gas is comparable to that measured optically.Comment: accepted to ApJ Letters, Oct 2000. 5 pages in emulateap

X-ray Evidence for Spectroscopic Diversity of Type Ia Supernovae: XMM observation of the elemental abundance pattern in M87

We present the results of a detailed element abundance study of hot gas in M87, observed by XMM-Newton. We choose two radial bins, 1'-3' and 8'-16' (8'-14' for EMOS; hereafter the central and the outer zones), where the temperature is almost constant, to carry out the detailed abundance measurements of O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni using EPIC-PN (EPN) and -MOS (EMOS) data. First, we find that the element abundance pattern in the central compared to the outer zone in M87 is characterized by SN Ia enrichment of a high (roughly solar) ratio of Si-group elements (Si, S, Ar, Ca) to Fe, implying that Si burning in SN Ia is highly incomplete. In nucleosynthesis modeling this is associated with either a lower density of the deflagration-detonation transition and/or lower C/O and/or lower central ignition density and observationally detected as optically subluminous SNe Ia in early-type galaxies. Second, we find that SN Ia enrichment has a systematically lower ratio of the Si-group elements to Fe by 0.2 dex in the outer zone associated with the ICM of the Virgo cluster. We find that such a ratio and even lower values by another 0.1 dex are a characteristic of the ICM in many clusters using observed Si:S:Fe ratios as found with ASCA. Third, the Ni/Fe ratio in the central zone of M87 is 1.5+/-0.3 solar (meteoritic), while values around 3 times solar are reported for other clusters. In modeling of SN Ia, this implies a reduced influence of fast deflagration SN Ia models in the chemical enrichment of M87's ISM. Thus, to describe the SN Ia metal enrichment in clusters, both deflagration as well as delayed detonation scenarios are required, supporting a similar conclusion, derived from optical studies on SNe Ia. Abridged.Comment: 11 pages, A&A, in pres

XMM-Newton and Gemini Observations of Eight RASSCALS Galaxy Groups

We study the distribution of gas pressure and entropy in eight groups of galaxies belonging to the ROSAT All-Sky Survey / Center for Astrophysics Loose Systems (RASSCALS). We use archival and proprietary XMM-Newton observations, supplementing the X-ray data with redshifts derived from the literature; we also list 127 new redshifts measured with the Gemini North telescope. The groups show remarkable self-similarity in their azimuthally averaged entropy and temperature profiles. The entropy increases with radius; the behavior of the entropy profiles is consistent with an increasing broken power law with inner and outer slope 0.92+0.04-0.05 and 0.42+0.05-0.04 (68% confidence), respectively. There is no evidence of a central, isentropic core, and the entropy distribution in most of the groups is flatter at large radii than in the inner region, challenging earlier reports as well as theoretical models predicting large isentropic cores or asymptotic slopes of 1.1 at large radii. The pressure profiles are consistent with a self-similar decreasing broken power law in radius; the inner and outer slopes are -0.78+0.04-0.03 and -1.7+0.1-0.3, respectively. The results suggest that the larger scatter in the entropy distribution reflects the varied gasdynamical histories of the groups; the regularity and self-similarity of the pressure profiles is a sign of a similarity in the underlying dark matter distributions.Comment: Accepted for publication in the Astrophysical Journa