G. Hertling

The XMM-LSS survey: the Class 1 cluster sample over the initial 5 deg2 and its cosmological modelling

We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5deg2 out to a redshift of z=1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses. The cluster distribution peaks around z=0.3 and T =1.5 keV, half of the objects being groups with a temperature below 2 keV. Our L-T(z) relation points toward self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z=1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the L-T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10deg2 has the potential to exclude the non-evolution hypothesis, but that constraints on more refined ICM models will probably be limited by the large intrinsic dispersion of the L-T relation. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to sigma8, Omega_m, L(M,z) and T(M,z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass-flux and mass-count-rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming SZ surveys.

The XMM-LSS survey: optical assessment and properties of different X-ray selected cluster classes

Context. XMM and Chandra opened a new area for the study of clusters of galaxies not only for cluster physics, but also for the detection of faint and distant clusters that were inaccessible with previous missions. Aims. This article presents 66 spectroscopically confirmed clusters (0.05 \textless= z \textless= 1.5) within an area of 6 deg(2) enclosed in the XMM-LSS survey. Almost two thirds have been confirmed with dedicated spectroscopy only and 10% have been confirmed with dedicated spectroscopy supplemented by literature redshifts. Methods. Sub-samples, or classes, of extended-sources are defined in a two-dimensional X-ray parameter space allowing for various degrees of completeness and contamination. We describe the procedure developed to assess the reality of these cluster candidates using the CFHTLS photometric data and spectroscopic information from our own follow-up campaigns. Results. Most of these objects are low-mass clusters, hence constituting a still poorly studied population. In a second step, we quantify the correlations between the optical properties such as richness or velocity dispersion and the cluster X-ray luminosities. We examine the relation of the clusters to the cosmic web. Finally, we review peculiar compact structures in the surveyed area such as very distant clusters and fossil groups.

Deep optical observations of the fields of two nearby millisecond pulsars with the VLT

Optical pulses from the Crab pulsar were detectedby Cocke, Disney and Taylor (1969) within a yearof the discovery of the pulsar in the radio band(Staelin & Reifenstein, 1968) and the inauguration ofthe field of pulsars by S. Jocelyn Bell and collabo-rators (Hewish et al. 1968). Since then, the number ofpulsars discovered in the radio band has gone up tonearly 1400 (ATNF pulsar catalogue), but the num-ber of pulsed counterparts detected in the high-energybands remains small. To date, in the optical bands,these remain 5, (Shearer & Golden 2002), and in theX-ray band 22, including 6 millisecond pulsars (MSP)(Becker & Aschenbach 2002). Multi-wavelength detectionof rotation-powered neutron stars provides observationalinput to the nature of the underlying mechanism of pulsarradiation, whether it is of thermal origin or due to radia-tion from accelerated particles in its magnetosphere (seee.g. Pavlov, Stringfellow, & Cordova 1996).Millisecond pulsars (MSP) are a special class, notonly because of their short spin periods, but also be-cause of their smaller surface magnetic field, old age,and evolutionary history of spin-up due to accretion ofmass and angular momentum from a binary companion(Alpar et al., 1982). In the process, the star may havebeen resurrected from a state of hibernation into one ofdetectable pulsed radio emission. They represent a consid-erable extension of the parameter space of classical pul-sars, so different radiation mechanisms may well be ac-tive in their magnetospheres. Their old age means thatthey have almost certainly radiated away any “fossil” heatfrom their original collapse or from their accretion epoch.

RCS 043938-2904.9: A new rich cluster of galaxies at z = 0.951

We present deep I, Js, Ks imaging and optical spectroscopy of the newly discovered Red-Sequence Cluster Survey cluster RCS 043938-2904.9. This cluster, drawn from an extensive preliminary list, was selected for detailed study on the basis of its apparent optical richness. Spectroscopy of 11 members places the cluster at z = 0.951 ± 0.006 and confirms the photometric redshift estimate from the (R-z) color-magnitude diagram. Analysis of the infrared imaging data demonstrates that the cluster is extremely rich, with excess counts in the Ks band exceeding the expected background counts by 9 σ. The properties of the galaxies in RCS 043938-2904.9 are consistent with those seen in other clusters at similar redshifts. Specifically, the red-sequence color, slope, and scatter and the size-magnitude relation of these galaxies are all consistent with that seen in the few other known high-redshift clusters and indeed are consistent with appropriately evolved properties of local cluster galaxies. The apparent consistency of these systems implies that the rich high-redshift RCS clusters are directly comparable to the few other systems known at z ~ 1, most of which have been selected on the basis of X-ray emission.

Advanced Camera for Surveys Observations of a Strongly Lensed Arc in a Field Elliptical Galaxy

We report the discovery of a strongly lensed arc system around a field elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images of a parallel field observed during NICMOS observations of the HST Ultra Deep Field. The ACS parallel data comprise deep imaging in the F435W, F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 16 from the galaxy center and subtends about 120°. Spectroscopic follow-up at Magellan Observatory yields a redshift z = 0.6174 for the lensing galaxy, and we photometrically estimate zphot = 2.4 ± 0.3 for the arc. We also identify a likely counterarc at a radius of 06 that shows structure similar to that seen in the main arc. We model this system and find a good fit to an elliptical isothermal potential of velocity dispersion σ ≈ 300 km s-1, the value expected from the fundamental plane, and some external shear. Several other galaxies in the field have colors similar to the lensing galaxy and likely make up a small group.We report the discovery of a strongly lensed arc system around a field elliptical galaxy in Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) images of a parallel field observed during NICMOS observations of the HST Ultra-Deep Field. The ACS parallel data comprise deep imaging in the F435W, F606W, F775W, and F850LP bandpasses. The main arc is at a radius of 1. 6 from the galaxy center and subtends about 120. Spectroscopic follow-up at Magellan Observatory yields a redshift z = 0.6174 for the lensing galaxy, and we photometrically estimate zphot = 2.4 ± 0.3 for the arc. We also identify a likely counter-arc at a radius of 0. 6, which shows structure similar to that seen in the main arc. We model this system and find a good fit to an elliptical isothermal potential of velocity dispersion σ ≈ 300 km s, the value expected from the fundamental plane, and some external shear. Several other galaxies in the field have colors similar to the lensing galaxy and likely make up a small group. Subject headings: galaxies: elliptical and lenticular, cD — cosmology: observations — gravitational lensing

Photometry of the Central Regions in a Complete Sample of High Bautz-Morgan-Type Abell Clusters. I. Observations and Data Calibration

We present CCD photometry of 209 southern Abell clusters selected according to Bautz-Morgan type I, I-II, and II. We have performed total photometry in the Gunn r bandpass, classified stars and galaxies, and obtained structural parameters for the images. To estimate the photometric and structural errors on the CCD images and the completeness limits of our photometry, we performed realistic simulations of stars and galaxies and ran our classification algorithms. Here, we present central galaxy counts and metric photometry of the brightest cluster members, for which we give accurate positions, and compare this photometry with values in the literature. A linear magnitude-redshift relation has been derived from the tenth-ranked galaxy in each cluster. Photometric redshifts have been estimated for 57 clusters. We provide either spectroscopic or photometric redshifts for all the clusters in our sample. Further analysis of these data will be presented in further publications.