arXiv subjects

M. Arnaud

Publications and source records attributed to M. Arnaud.

At least 217 records · Page 12Linked to original sources

arXiv2005

Chandra observation of the multiple merger cluster Abell 521

We present the Chandra analysis of the galaxy cluster A521 (z=0.247). The high resolution of the Chandra observation has allowed us to refine the original merging scenario proposed for A521, and to reveal new features in its X-ray emission. A521 has strongly substructured ICM density and temperature maps. Its X-ray diffuse emission is elongated along a NW/SE direction (SX2) and shows two major components, a main cluster and a northern group of galaxies. This latter is in turn substructured, showing a clump of cold and very dense gas centred on the BCG, and a northern tail aligned in the SX2 direction. A compression of the X-ray isophotes is also observed South of the BCG. We conclude that the northern group is infalling onto the main cluster along the NW/SE direction. This hypothesis is corroborated by the presence of a hot bar in the ICM temperature map located between the southern and northern regions, as the gas could be compressionally heated due to the subclusters' collision. The hot region corresponds to the eastern part of an over-dense ridge of galaxies, along which it was originally suggested that a merging of subclusters has recently occurred along the line of sight. An alternative hypothesis about the origin of the hot central bar is that we could observe in projection the shock fronts due to this older cluster-cluster collision. Two other structures possibly interacting with the main cluster are detected on the West and North-East sides of the BCG. We also uncover the presence of two northern edges in the ICM density. A521 is a spectacular example of a multiple merger cluster made up by several substructures converging at different epochs towards the centre of the system. The very pertubed dynamical state of this cluster is also confirmed by our discovery of a radio relic in its South-East region.

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arXiv2005

X-ray observations of Clusters of Galaxies

X-ray observations of clusters provide key information on the dark matter, on the formation of structures in the Universe, and can be used to constrain the cosmological parameters. I review our current knowledge, with emphasis on recent XMM and Chandra results.

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arXiv2005

The structural and scaling properties of nearby galaxy clusters - II. The M-T relation

Using a sample of ten nearby (z< 0.15), relaxed galaxy clusters in the temperature range [2-9] keV, we have investigated the scaling relation between the mass at various density contrasts (delta=2500,1000,500,200) and the cluster temperature. The masses are derived from NFW-type model fits to mass profiles, obtained under the hydrostatic assumption using precise measurements, with XMM, at least down to delta=1000. The logarithmic slope of the M-T relation is well constrained and is the same at all delta, reflecting the self-similarity of the mass profiles. At delta=500, the slope of the relation for the sub-sample of hot clusters (kT>3.5 keV) is consistent with the standard self-similar expectation: alpha= 1.49\pm0.15. The relation steepens when the whole sample is considered: alpha=1.71\pm0.09. The normalisation of the relation is discrepant (by ~ 30%), at all density contrasts, with the prediction from purely gravitation based models. Models that take into account radiative cooling and galaxy feedback are generally in better agreement with our data. We argue that remaining discrepancies, in particular at low delta, are more likely due to problems with models of the ICM thermal structure rather than to an incorrect estimate of the mass from X-ray data.

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arXiv2005

Probing the dark matter profile of hot clusters and the M-T relation with XMM-Newton

We present results based on XMM-Newton observations of a small sample of hot galaxy clusters. Making a full use of XMM-Newton's spectro-imaging capabilities, we have extracted the radial temperature profile and gas density profile, and with this information, calculated the total mass profile of each cluster (under the assumption of hydrostatic equilibrium and spherical symmetry). Comparing the individual scaled total mass profiles, we have probed the Universality of rich cluster mass profiles over a wide range of radii (from 0.01 to 0.7 the virial radius). We have also tested the shape of cluster mass profiles by comparing with the predicted profiles from numerical simulations of hierarchical structure formation. We also derived the local mass-temperature (M-T) scaling relation over a range of temperature going from 4 to 9 keV, that we compare with theoretical predictions.

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arXiv2005

The structural and scaling properties of nearby galaxy clusters: I - The universal mass profile

We present the integrated mass profiles for a sample of ten nearby (z<=0.15), relaxed galaxy clusters, covering a temperature range of [2-9]keV, observed with XMM-Newton. The mass profiles were derived from the observed gas density and temperature profiles under the hypothesis of spherical symmetry and hydrostatic equilibrium. All ten mass profiles are well described by an NFW-type profile over the radial range from 0.01 to 0.5 R_200, where R_200 is the radius corresponding to a density contrast of 200 with respect to the critical density at the cluster redshift. A King model is inconsistent with these data. The derived concentration parameters and total masses are in the range c_200=4-6 and M_200=1.2 10^14-1.2 10^15 Msol, respectively. Our qualitative and quantitative study of the mass profile shape shows, for the first time, direct and clear observational evidence for the universality of the total mass distribution in clusters. The mass profiles scaled in units of R_200 and M_200 nearly coincide, with a dispersion of less than 15% at 0.1 R_200. The c_200--M_200 relation is consistent with the predictions of numerical simulations for a LCDM cosmology, taking into account the measurement errors and expected intrinsic scatter. Our results provide further strong evidence in favour of the Cold Dark Matter cosmological scenario and show that the dark matter collapse is well understood at least down to the cluster scale.

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arXiv2004

XMM-Newton observations of three poor clusters: Similarity in dark matter and entropy profiles down to low mass

(Abridged) We present an analysis of the mass and entropy profiles of three poor clusters (A1991, A2717 and MKW9) observed with XMM-Newton. The clusters have similar temperatures (kT=2.65, 2.53 and 2.58 keV), and similar redshifts (0.04 < z < 0.06). We trace the surface brightness, temperature, entropy and integrated mass profiles up to 0.5 (0.35 for MKW9) of the virial radius (r_200). The integrated mass profiles are very similar in physical units and are reasonably well fitted with the NFW mass model with concentration parameters of c_200=4-6 and M_200=1.2-1.6 X 10^14 h_70^-1 \msun. The entropy profiles are similar at large scale, but there is some scatter in the central region (r<50 kpc). None of the clusters has an isentropic core. Including XMM data on A1983 (kT=2.2 keV), and A1413 (kT = 6.5 keV), we discuss the structural and scaling properties of cluster mass and entropy profiles. The scaled mass profiles display <20% dispersion in the 0.05 - 0.5 r_200 radial range. The c_200 parameters of these clusters, and other values from the literature, are fully consistent with the c_200 - M_200 relation derived from simulations. The dispersion in scaled entropy profiles is small, implying self-similarity down to low mass (kT ~2 keV), and is reduced by 30-40% (to ~20%) if we use the empirical relation S \propto T^0.65 instead of the standard self-similar relation, S \propto T. The mean scaled profile is well fitted by a power law for 0.05 < r_200 < 0.5, with a slope slightly lower than expected from pure shock heating (α= 0.94+/-0.14), and a normalisation at 0.1 r_200 consistent with previous studies. The gas history thus likely depends both on gravitational processes and the interplay between cooling and various galaxy feedback mechanisms.

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arXiv2004

Introducing BAX: a database for X-ray clusters and groups of galaxies

We present BAX, Base de Donnees Amas de Galaxies X (http://webast.ast.obs-mip.fr/bax), a multi-wavelength database dedicated to X-ray clusters and groups of galaxies allowing detailed information retrieval. BAX is designed to support astronomical research by providing access to published measurements of the main physical quantities and to the related bibliographic references: basic data stored in the database are cluster/group identifiers, equatorial coordinates, redshift, flux, X-ray luminosity (in the ROSAT band) and temperature, and links to additional linked parameters (in X-rays, such as spatial profile parameters, as well as SZ parameters of the hot gas, lensing measurements,and data at other wavelengths, such as optical and radio). The clusters and groups in BAX can be queried by the basic parameters as well as the linked parameters or combinations of these. We expect BAX to become an important tool for the astronomical community. BAX will optimize various aspects of the scientific analysis of X-ray clusters and groups of galaxies, from proposal planning to data collection, interpretation and publication, from both ground based facilities like MEGACAM (CFHT), VIRMOS (VLT) and space missions like XMM-Newton, Chandra and Planck.

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arXiv2004

XMM-Newton observation of the relaxed cluster A478: gas and dark matter distribution from 0.01 R_200 to 0.5 R_200

We present an \xmm mosaic observation of the hot ($kT\sim6.5$ keV) and nearby ($z=0.0881$) relaxed cluster of galaxies A478. We derive precise gas density, gas temperature, gas mass and total mass profiles up to $12\arcmin$ (about half of the virial radius $R_{200}$). The gas density profile is highly peaked towards the center and the surface brightness profile is well fitted by a sum of three $β$--models. The derived gas density profile is in excellent agreement, both in shape and in normalization, with the published Chandra density profile (measured within $5\arcmin$ of the center). Projection and PSF effects on the temperature profile determination are thoroughly investigated. The derived radial temperature structure is as expected for a cluster hosting a cooling core, with a strong negative gradient at the cluster center. The temperature rises from $\sim2$ keV up to a plateau of $\sim6.5$ keV beyond 2' (i.e. $r>208\rm{kpc}=0.1 R_{200}$, $R_{200}=2.08$ Mpc being the virial radius). From the temperature profile and the density profile and under the hypothesis of hydrostatic equilibrium, we derived the total mass profile of A478 down to 0.01 and up to 0.5 the virial radius. We tested different dark matter models against the observed mass profile. The Navarro, Frenk & White (\cite{navarro97}) model is significantly preferred to other models. It leads to a total mass of $M_{200}=1.1\times 10^{15}$ M$_\odot$ for a concentration parameter of $c=4.2\pm0.4$. The gas mass fraction slightly increases with radius. The gas mass fraction at a density contrast of $δ=2500$ is $\fgas=0.13\pm0.02$, consistent with previous results on similar hot and massive clusters. We confirm the excess of absorption in the direction of A478.[abridged]

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arXiv2003

Structural and scaling properties of galaxy clusters: probing the physics of structure formation

We present XMM-Newton studies of the total mass, gas density, temperature and entropy profiles in nearby hot and cool clusters, together with follow-up observations of distant clusters from the SHARC Survey. The observed structural and scaling properties are compared with the predictions of the self-similar model of cluster formation. These data indicate that clusters do form a self-similar population down to low mass and up to high redshift, and give support to the standard picture of structure formation for the dark matter component. However, deviations from the standard scaling laws confirm that the specific physics of the gas component is still insufficiently understood.

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arXiv2003

SIMBOL-X : a new generation hard X-ray telescope

SIMBOL-X is a hard X-ray mission, operating in the 0.5-70 keV range, which is proposed by a consortium of European laboratories for a launch around 2010. Relying on two spacecraft in a formation flying configuration, SIMBOL-X uses a 30 m focal length X-ray mirror to achieve an unprecedented angular resolution (30 arcsec HEW) and sensitivity (100 times better than INTEGRAL below 50 keV) in the hard X-ray range. SIMBOL-X will allow to elucidate fundamental questions in high energy astrophysics, such as the physics of accretion onto Black Holes, of acceleration in quasar jets and in supernovae remnants, or the nature of the hard X-ray diffuse emission. The scientific objectives and the baseline concepts of the mission and hardware design are presented.

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arXiv2003

Entropy scaling in galaxy clusters: insights from an XMM-Newton observation of the poor cluster A1983

An XMM-Newton observation of the cool (kT=2.1 keV) cluster A1983, at z=0.044, is presented. Gas density and temperature profiles are calculated for the inner 500 h_{50}^{-1} kpc (~0.35 r_200). The outer regions of the surface brightness profile are well described with a beta model with beta=0.74, but the central regions require the introduction of a second component. The temperature profile is flat at the exterior with a slight dip towards the centre. The total mass profile, calculated assuming hydrostatic equilibrium, is consistent with an NFW profile, but with a low concentration parameter c=3.75 +/- 0.74. The M/L_B ratio profile shows that, at large scale, light traces mass to a reasonable extent, and the M/L_B ratio at 0.35 r_200 is consistent with the trends with mass observed in the optical. The M_Fe/L_B ratio is about two times less than that observed for a cluster at 5 keV. The gas mass fraction rises rapidly to level off at ~200 kpc; the value at 0.35 r_200 is ~8%. The scaling properties of the emission measure profile are consistent with the empirical relation \mgas \propto \Tx^{1.94}, and not with the self-similar relation \mgas \propto \Tx^{1.5}. Comparison of the entropy profile of A1983 with that of the hot cluster A1413 shows that the profiles are well scaled using the empirically determined relation S \propto \Tx^{0.65}, suggesting that the slope of the S-T relation is shallower than in the self-similar model. The form of the entropy profiles is remarkably similar, and there is no sign of a larger isentropic core in the cooler cluster. These data provide powerful agruments against preheating models. In turn, there is now increasing observational support for a trend of f_gas with system mass, which may go some way towards explaining the observed scaling behaviour. (Abridged.)

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arXiv2003

The origin of X-ray emission of two distant (z>1) cluster candidate with XMM-Newton

We present here a study of XMM-Newton data of two distant galaxy cluster candidates. One of these was discovered serendipitously in near infrared data, CL J0533-2411, the other one corresponds to the cluster EIS J0533-2412 part of the EIS cluster survey. The estimated redshift of CL J0533-2411 is z=1.2-1.7. EIS J0533-2412 is a rich system (Lambda_cl=299), with a spectroscopically confirmed redshift of z=1.3. Both galaxy concentrations show firm X-ray detections, located within 30" of their optical center. However, we cannot resolve the sources with XMM-Newton. If the X-ray emission originates from the X-ray emitting intra-cluster medium (ICM) it would be extremely concentrated which is rather unlikely (core radii below 14 h_{65}^{-1}kpc and 40 h_{65}^{-1}kpc, respectively). We argue that the X-ray sources are more likely AGN members of the galaxy concentrations. We set an upper limit for the bolometric luminosity of a hot ICM in the range ~0.7-2.1 10^{44} h_{65}^{-2}erg/s for CL J0533-2411, depending on the exact redshift. For EIS J0533-2412 the limit is L_bol=(6.2+/-1.4) 10^{43} h_{65}^{-2}erg/s. We interpret our result in the following way: EIS J0533-2412 (and possibly CL J0533-2411) are proto-clusters and show matter overdensities before collapse, which explains the low significance of extended X-ray emission.

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arXiv2002

The mass profile of A1413 observed with XMM-Newton: implications for the M-T relation

We present an XMM-Newton observation of A1413, a hot (kT = 6.5 keV) galaxy cluster at z=0.143. We construct gas and temperature profiles up to ~1700 kpc, equivalent to ~0.7 r_200. The gas distribution is well described by a beta model in the outer regions, but is more concentrated in the inner ~250 kpc. We introduce a new parameterisation for the inner regions, allowing a steeper gas density distribution. The projected radial temperature profile declines gradually towards the outer regions, by ~20% between 0.1 r_200 and 0.5 r_200, and is well described by a polytropic model with gamma = 1.07+/-0.01. We find that neither projection nor PSF effects change substantially the form of the temperature profile. Assuming hydrostatic equilibrium (HE) and spherical symmetry, we use the observed temperature profile and the new parametric form for the gas density profile to produce the total mass distribution. The mass profile is remarkably well fitted with the Moore et al. (1999) parameterisation with a concentration parameter in the range expected from numerical simulations. There are several indications that beyond a density contrast delta \~600, the gas may no longer be in HE. There is an offset with respect to adiabatic numerical simulations in the virialised part of the cluster, in that the predicted mass for the cluster temperature is ~40% too high. The gas distribution is peaked in the centre primarily as a result of the cusp in the dark matter profile. The X-ray gas to total mass ratio rises with increasing radius to f_gas ~ 0.2. These data strongly support the validity of the current approach for the modelling of the dark matter collapse, but confirm that understanding the gas specific physics is essential. (Abridged)

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arXiv2002

Optically-selected clusters at 0.8 < z < 1.3 in the EIS Cluster Survey

This paper presents preliminary results of a spectroscopic survey being conducted at the VLT of fields with optically-selected cluster candidates identified in the EIS I-band survey. Here we report our findings for three candidates selected for having estimated redshifts in the range z=0.8-1.1. New multi-band optical/infrared data were used to assign photometric redshifts to galaxies in the cluster fields and to select possible cluster members in preparation of the spectroscopic observations. Based on the available spectroscopic data, which includes 147 new redshifts for galaxies with Iab<22-23, we confirm the detection of four density enhancements at a confidence level >99%. The detected concentrations include systems with redshifts z=0.81, z=0.95, z=1.14 and the discovery of the first optically-selected cluster at z=1.3. The latter system, with three concordant redshifts, coincides remarkably well with the location of a firm X-ray detection (>5sigma) in a ~80ksec XMM-Newton image taken as part of this program which will be presented in a future paper (Neumann et al. 2002). The z>1 systems presented here are possibly the most distant identified so far by their optical properties alone.

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arXiv2002

XMM-Newton observation of the distant (z=0.6) galaxy cluster RX J1120.1+4318

We report on a 20 ksec XMM observation of the distant cluster RXJ1120.1+4318, discovered at z=0.6 in the SHARC survey. The cluster has a regular spherical morphology, suggesting it is in a relaxed state. The combined fit of the EPIC/MOS&pn camera gives a cluster mean temperature of kT=5.3\pm0.5 keV with an iron abundance of 0.47\pm0.19. The temperature profile, measured for the first time at such a redshift, is consistent with an isothermal atmosphere up to half the virial radius. The surface brightness profile, measured nearly up to the virial radius, is well fitted by a beta-model, with beta =0.78[+0.06,-0.04] and a core radius of thetac = 0.44[+0.06,-0.04] arcmin. We compared the properties of RXJ1120.1+4318 with the properties of nearby clusters for two cosmological models: an Einstein - de Sitter Universe and a flat low density Universe with Omega0=0.3. For both models, the scaled emission measure profile beyond the core, the gas mass fraction and luminosity are consistent with the expectations of the self-similar model of cluster formation, although a slightly better agreement is obtained for a low density Universe. There is no evidence of a central cooling flow, in spite of the apparent relaxed state of the cluster. This is consistent with its estimated cooling time, larger than the age of the Universe at the cluster redshift. The entropy profile shows a flat core with a central entropy of ~ 140 keV cm^2, remarkably similar to the entropy floor observed in nearby clusters, and a rising profile beyond typically 0.1 virial radius. Implications of our results, in terms of non-gravitational physics in cluster formation, are discussed.

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arXiv2002

The X-ray surface brightness profiles of hot galaxy clusters up to z~0.8: evidence for self-similarity and constraints on Omega_0

We study the ROSAT surface brightness profiles of a sample of 25 distant (0.3 3.5keV) clusters. For both open and flat cosmological models, the derived emission measure profiles are scaled according to the self-similar model of cluster formation. We use the standard scaling relations of cluster properties with z and temperature, with the empirical slope of the Mgas-T relation derived by Neumann & Arnaud (2001). Using a χ^2 test, we perform a quantitative comparison of the scaled emission measure profiles of distant clusters with a reference profile derived from the sample of 15 hot nearby clusters compiled by Neumann & Arnaud (1999), which were found to obey self-similarity. For a low density flat universe, the distant cluster scaled data were found to be consistent, both in shape and normalisation, with the reference local profile.It indicates that hot clusters constitute a homologous family up to high z, and supports the standard picture of structure formation for the dark matter component. Because of the intrinsic regularity in the hot cluster population, the scaled profiles can be used as distance indicators, the correct cosmology being the one for which the profiles at different redshifts coincide. The present data allow us to put a tight constraint on Omega0 for a flat Universe: Omega0=0.40^{+0.15}_{-0.12} at 90% confidence level (statistical errors only). The critical model was excluded at the 98% confidence level. Consistently, the observed evolution of the normalisation of the Lx-T relation was found to comply with the self-similar model for Omega0=0.4, Lambda=0.6. The constraint derived on Omega0 is in remarkable agreement with the constraint obtained from SNI or from combined analysis of the power spectrum of the 2dFGRS and the CMB anisotropy. ABRIDGED

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arXiv2002

Status of the EPIC/MOS calibration

The XMM-Newton observatory has the largest collecting area flown so far for an X-ray imaging system, resulting in a very high sensitivity over a broad spectral range. In order to exploit fully these performances, a very accurate calibration of the XMM-Newton instruments is required, and has led to an extensive ground and flight calibration program. We report here on the current status of the EPIC/MOS cameras calibrations, highlighting areas for which a reasonably good accuracy has been achieved, and noting points where further work is needed.

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arXiv2001

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.

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