arXiv subjects

S. Dos Santos

Publications and source records attributed to S. Dos Santos.

9 recordsLinked to original sources

arXiv2005

The XMM Large-Scale Structure Survey: An initial sample of galaxy groups and clusters to a redshift z<0.6

We present X-ray and optical spectroscopic observations of twelve galaxy groups and clusters identified within the XMM Large-Scale Structure (LSS) survey. Groups and clusters are selected as extended X-ray sources from a 3.5 deg2 XMM image mosaic above a flux limit 8e-15 ergs/s/cm2 in the [0.5-2] keV energy band. Deep BVRI images and multi-object spectroscopy confirm each source as a galaxy concentration located within the redshift interval 0.29<z<0.56. We combine line-of-sight velocity dispersions with the X-ray properties of each structure computed from a two-dimensional surface brightness model and a single temperature fit to the XMM spectral data. The resulting distribution of X-ray luminosity, temperature and velocity dispersion indicate that the XMM-LSS survey is detecting low-mass clusters and galaxy groups to redshifts z < 0.6. Confirmed systems display little or no evidence for X-ray luminosity evolution at a given X-ray temperature compared to lower redshift X-ray group and cluster samples. A more complete understanding of these trends will be possible with the compilation of a statistically complete sample of galaxy groups and clusters anticipated within the continuing XMM-LSS survey.

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arXiv2004

The XMM-LSS survey. Survey design and first results

We have designed a medium deep large area X-ray survey with XMM - the XMM Large Scale Structure survey, XMM-LSS - with the scope of extending the cosmological tests attempted using ROSAT cluster samples to two redshift bins between 0<z<1 while maintaining the precision of earlier studies. Two main goals have constrained the survey design: the evolutionary study of the cluster-cluster correlation function and of the cluster number density. The results are promising and, so far, in accordance with our predictions as to the survey sensitivity and cluster number density. The feasibility of the programme is demonstrated and further X-ray coverage is awaited in order to proceed with a truly significant statistical analysis. (Abridged)

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arXiv2004

The XMM-LSS Survey. First high redshift galaxy clusters: relaxed and collapsing systems

We present five newly found galaxy clusters at z>0.6 from the XMM Large-Scale Structure Survey (XMM-LSS). All five objects are extended X-ray sources in the XMM images. For three of them we have sufficient spectroscopically confirmed member galaxies that an estimate of the velocity dispersion is possible: XLSSC 001 at z=0.613 and σ_V=867^{+80}_{-60} km/s, XLSSC 002 at z=0.772 and σ_V=524^{+267}_{-116} km/s and XLSSC 003 at z=0.839 and σ_V=780^{+137}_{-75} km/s. These three clusters have X-ray bolometric luminosities L_X \sim 1-3 \times 10^{44} erg/s and temperatures 2-4 keV, and consequently are less massive than previously known clusters at similar redshifts, but nevertheless they follow the low redshift scaling relations between L_X, T and σ_V, within the limits of the measurement errors. One of the clusters, XLSSC 004, is detected independently as an overdensity of galaxies of a colour R-z'=1.4 that matches the redshift of the central galaxy z=0.87, although it cannot unambiguously be confirmed by the spectroscopic observations alone. The highest redshift candidate cluster pertaining to this paper, XLSSC 005, is most likely a double cluster complex at a redshift around unity, associated with an extended X-ray source with probable substructure.

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arXiv2001

Competition between shocks and entropy floor : unifying groups and clusters of galaxies

Semi-analytic models of X-ray clusters and groups of galaxies, relying on the idea that there was a non-gravitational energy injection in these systems, are able to reproduce many observed correlations, in particular the L_X-T relation and the ``central entropy floor'' in groups. Limiting models exist which describe the behaviour of clusters and groups separately, but no analytic modeling has yet been found to unify both mass ranges. {\it It is the aim of this paper to provide such an analytic model.} Our description relies on a now standard description of the shock thought to occur in these systems near the virial radius (Cavaliere et al., 98), the isothermality and spherical symmetry of the intracluster medium, as well as the reinterpretation of observed quantities (like the X-ray luminosity, the gas mass M_{ICM} and the central SZ effect y_0) in terms of the specific entropy. This allows the derivation of analytic expressions for several observed correlations (L_X-T, M_{ICM}-T, y_0-T,...) and their normalisation encompassing \emph{both the group and the cluster regimes}. The analytic predictions compare very well with observations, as well as with more elaborated semi-analytic schemes. This agreement allows a reinterpretation of the L_X-T relation (via the quantity L_X/T^{7/2}) and the y_0-T relation (via y_0/T^{5/2}) as indirect measures of the non-gravitational entropy content of groups and clusters of galaxies. Finally, we emphasize the need for shock heating, even in the group mass range : \emph{shocks can not be completely supressed in groups} (and thus groups can not be entirely isentropic) unless an unacceptably high entropy floor is needed in order to break the self-similarity in the L_X-T relation.

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arXiv2001

A Comparison of the EUV and X-Ray Emission Profiles in Six Clusters of Galaxies

We have performed the wavelet analysis and image reconstructions for six clusters of galaxies observed both at extreme ultraviolet and X-ray energies. The comparison of the profiles of the EUV and X-ray reconstructed images shows that they differ at a very large confidence level in five of the six clusters, and are similar only for the Coma cluster, which is by far the hottest one in the sample.

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arXiv2000

XMM-Newton observations of M87 and Its X-Ray Halo

We report performance verification observations of the giant elliptical galaxy M87 in the Virgo Cluster with the MOS, pn, and optical monitor instruments on board of XMM-Newton. With the energy sensitive imaging instruments MOS and pn we obtain the first spatially constrained X-ray spectra of the nucleus and the jet of the galaxy. The good photon statistics of the pn and MOS allow a detailed analysis of the radial temperature and abundance distribution of 6 elements. The data provide no indication of a multi-temperature structure for radii less than 2 arcmin. An apparent sharp metal abundance drop deduced for the regions inside this radius is probably due to resonant line scattering.

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arXiv2000

Steady-state conduction-driven temperature profile in clusters of galaxies

The temperature profile (TP) of the intracluster medium (ICM) is of primeval importance for deriving the dynamical parameters of the largest equilibrium systems known in the universe, in particular their total mass profile. Analytical models of the ICM often assume that the ICM is isothermal or parametrize the TP with a polytropic index. This parameter is ajusted to observations, but has in fact poor physical meaning for values other than 1 or 5/3, when considering monoatomic gases. In this article, I present a theoretical model of a relaxed cluster where the TP is instead structured by electronic thermal conduction. Neglecting cooling and heating terms, the stationnary energy conservation equation reduces to a 2nd order differential equation, whose resolution requires two boundary conditions, taken here as the inner radius and the ratio between inner and outer temperature. Once these two constants are chosen, the TP has a fixed analytical expression, which reproduces nicely the observed ``universal'' TP obtained by Markevitch et al. (1998) from ASCA data. Using observed X-ray surface brightnesses for two hot clusters with spatially resolved TP, the local polytropic index and the hot gas fraction profile are predicted and compare very well with ASCA observations (Markevitch et al 1999). Moreover, the total density profile derived from observed X-ray surface brightness, hydrostatic equilibrium and the conduction-driven TP is very well fit by three analytical profiles found to describe the structure of galactic or cluster halos in numerical simulations of collisionless matter (Hernquist, 1991; Navarro et al. 1995, 1997; Burkert 1995). (abriged)

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arXiv1999

Re-observing the EUV emission from Abell 2199: in-situ measurement of background distribution by offset pointing

The EUV excess emission from the clusters A2199 and A1795 remains an unexplained astrophysical phenomenon. There has been many unsuccessful attempts to `trivialize' the findings. In this Letter we present direct evidence to prove that the most recent of such attempts, which attributes the detected signals to a background non-uniformity effect, is likewise excluded. We address the issue by a re-observation of A2199 which features a new filter orientation, usage of a more sensitive part of the detector and, crucially, includes a background pointing at $\sim$ 2$^o$ offset - the first {\it in situ} measurement of its kind. We demonstrate quantitatively two facts: (a) the offset pointing provides an accurate background template for the cluster observation, while (b) data from other blank fields do not. We then performed point-to-point subtraction of the {\it in situ} background from the cluster field, with appropriate propagation of errors. The resulting cluster radial profile is consistent with that obtained by our original method of subtracting a flat asymptotic background. The emission now extends to a radius of 20 arcmin; it confirms the rising prominence of EUV excess beyond $\sim$ 5 arcmin as previously reported.

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arXiv1999

Clumpy diffuse X-ray emission from the spiral-rich compact galaxy group HCG16

We reanalyze the ROSAT PSPC X-ray spectro-photometric observations of HCG 16. Its X-ray morphology resembles its morphology at 20 cm, seen by the NVSS. We detect diffuse emission in 8 regions filling half of the 200/h50 kpc (8.7") radius circle around the optical center of the group: one encompassing galaxies a&b, two surrounding galaxies c&d, a clumpy region roughly 140/h50 kpc from the group galaxies, which may be gas ejected from one of the galaxies, plus regions associated with background galaxies, radio-sources or groups, and foreground stars. Excluding the background / foreground sources, we get L_X^bol = 2.3 10^41 / h50^2 erg/s, i.e. half the luminosity found by Ponman et al. The diffuse emission is cool (T < 0.55 keV [90% confidence] with a best fit T = 0.27 keV). The correction for photoelectric absorption in L_X^bol is a factor 3.5 and varies rapidly with temperature. The clumpy distribution of hot diffuse gas in HCG 16 is illustrated by the low mean X-ray surface brightness and hot gas density of the regions of undetected emission within 8' (at most 1/4 and 1/6 of those of the detected gas, assuming both have same temperature, metallicity and clumpiness). The irregular X-ray morphology of the diffuse emission rules out a (nearly) virialized nature for HCG 16, unless intergalactic gas had sufficiently high specific entropy to be unable to collapse with the group. Most of the diffuse gas originates from galaxies, either through tidal stripping or through galactic winds driven by supernova remnants. Our results show the need for a careful 2D spatial analysis and multi-wavelength study of the diffuse X-ray emission from groups, suggesting that other compact groups could be significantly contaminated by superimposed X-ray sources.(abridged)

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