We perform a weak lensing analysis on a previously reported dark-lens candidate on STIS Parallel data CITE. New VLT-data indicate that the reported signal originates from a small number of galaxies ...tangentially aligned towards the center of the STIS field but no signature for an extended mass distribution is found. We argue that we should be able to detect a massive cluster ($M\geq 3.2\times 10^{14}~M_{\odot}$) through its lensing signal up to a redshift of $z\approx 0.6$ with our data. Also the double image hypothesis of two galaxies with very similar morphologies in the STIS data is ruled out with colour information.
We present a spectroscopic catalog of the neighboring massive clusters Abell 222 and Abell 223. The catalog contains the positions, redshifts, R magnitudes, $V-R$ color, as well as the equivalent ...widths for a number of lines for 183 galaxies, 153 of them belonging to the A 222 and A 223 system. We determine the heliocentric redshifts to be $z=0.2126\pm0.0008$ for A 222 and $z=0.2079\pm0.0008$ for A 223. The velocity dispersions of both clusters in the cluster restframe are about the same: $\sigma = {1014}^{+90}_{-71}$ km s-1 and $\sigma = {1032}^{+99}_{-76}$ km s-1 for A 222 and A 223, respectively. While we find evidence for substructure in the spatial distribution of A 223, no kinematic substructure can be detected. From the red cluster sequence identified in a color–magnitude–diagram we determine the luminosity of both clusters and derive mass–to–light ratios in the R–band of $(M/L)_{{\rm A222}} = (202 \pm 43)~h_{70}~M_{\odot}/L_{\odot}$ and $(M/L)_{{\rm A223}} = (149 \pm 33)~h_{70}~M_{\odot}/L_{\odot}$. Additionally we identify a group of background galaxies at $z \sim 0.242$.
Context. Constraints on the mass distribution in high-redshift clusters of galaxies are currently not very strong. Aims. We aim to constrain the mass profile, M(r), and dynamical status of the z ~ ...0.8 LCDCS 0504 cluster of galaxies that is characterized by prominent giant gravitational arcs near its center. Methods. Our analysis is based on deep X-ray, optical, and infrared imaging as well as optical spectroscopy, collected with various instruments, which we complemented with archival data. We modeled the mass distribution of the cluster with three different mass density profiles, whose parameters were constrained by the strong lensing features of the inner cluster region, by the X-ray emission from the intracluster medium, and by the kinematics of 71 cluster members. Results. We obtain consistent M(r) determinations from three methods based on kinematics (dispersion-kurtosis, caustics, and MAMPOSSt), out to the cluster virial radius, ≃1.3 Mpc and beyond. The mass profile inferred by the strong lensing analysis in the central cluster region is slightly higher than, but still consistent with, the kinematics estimate. On the other hand, the X-ray based M(r) is significantly lower than the kinematics and strong lensing estimates. Theoretical predictions from ΛCDM cosmology for the concentration–mass relation agree with our observational results, when taking into account the uncertainties in the observational and theoretical estimates. There appears to be a central deficit in the intracluster gas mass fraction compared with nearby clusters. Conclusions. Despite the relaxed appearance of this cluster, the determinations of its mass profile by different probes show substantial discrepancies, the origin of which remains to be determined. The extension of a dynamical analysis similar to that of other clusters of the DAFT/FADA survey with multiwavelength data of sufficient quality will allow shedding light on the possible systematics that affect the determination of mass profiles of high-z clusters, which is possibly related to our incomplete understanding of intracluster baryon physics.
We present preliminary results about the detection of high redshift (U)LIRGs in the Bullet cluster field by the PACS and SPIRE instruments within the Herschel Lensing Survey (HLS) Program. We ...describe in detail a photometric procedure designed to recover robust fluxes and deblend faint Herschel sources near the confusion noise. The method is based on the use of the positions of Spitzer/MIPS 24 μm sources as priors. Our catalogs are able to reliably (5σ) recover galaxies with fluxes above 6 and 10 mJy in the PACS 100 and 160 μm channels, respectively, and 12 to 18 mJy in the SPIRE bands. We also obtain spectral energy distributions covering the optical through the far-infrared/millimeter spectral ranges of all the Herschel detected sources, and analyze them to obtain independent estimations of the photometric redshift based on either stellar population or dust emission models. We exemplify the potential of the combined use of Spitzer position priors plus independent optical and IR photometric redshifts to robustly assign optical/NIR counterparts to the sources detected by Herschel and other (sub-)mm instruments. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Context. Constraints on the mass distribution in high-redshift clusters of galaxies are currently not very strong. Aims. We aim to constrain the mass profile, M(r), and dynamical status of the z ...similar to 0.8 LCDCS 0504 cluster of galaxies that is characterized by prominent giant gravitational arcs near its center. Methods. Our analysis is based on deep X-ray, optical, and infrared imaging as well as optical spectroscopy, collected with various instruments, which we complemented with archival data. We modeled the mass distribution of the cluster with three different mass density profiles, whose parameters were constrained by the strong lensing features of the inner cluster region, by the X-ray emission from the intracluster medium, and by the kinematics of 71 cluster members. Results. We obtain consistent M(r) determinations from three methods based on kinematics (dispersion-kurtosis, caustics, and MAMPOSSt), out to the cluster virial radius, similar or equal to 1.3 Mpc and beyond. The mass profile inferred by the strong lensing analysis in the central cluster region is slightly higher than, but still consistent with, the kinematics estimate. On the other hand, the X-ray based M(r) is significantly lower than the kinematics and strong lensing estimates. Theoretical predictions from Lambda CDM cosmology for the concentration-mass relation agree with our observational results, when taking into account the uncertainties in the observational and theoretical estimates. There appears to be a central deficit in the intracluster gas mass fraction compared with nearby clusters. Conclusions. Despite the relaxed appearance of this cluster, the determinations of its mass profile by different probes show substantial discrepancies, the origin of which remains to be determined. The extension of a dynamical analysis similar to that of other clusters of the DAFT/FADA survey with multiwavelength data of sufficient quality will allow shedding light on the possible systematics that affect the determination of mass profiles of high-z clusters, which is possibly related to our incomplete understanding of intracluster baryon physics.
We present spectroscopic observations of galaxies in 4 clusters at $z = 0.7{-}0.8$ and in one cluster at $z \sim 0.5$ obtained with the FORS2 spectrograph on the VLT as part of the ESO Distant ...Cluster Survey (EDisCS), a photometric and spectroscopic survey of 20 intermediate to high redshift clusters. We describe our target selection, mask design, observation and data reduction procedures, using these first 5 clusters to demonstrate how our strategies maximise the number of cluster members for which we obtain spectroscopy. We present catalogues containing positions, I-band magnitudes and spectroscopic redshifts for galaxies in the fields of our 5 clusters. These contain 236 cluster members, with the number of members per cluster ranging from 30 to 67. Our spectroscopic success rate, i.e. the fraction of spectroscopic targets which are cluster members, averages 50% and ranges from 30% to 75%. We use a robust biweight estimator to measure cluster velocity dispersions from our spectroscopic redshift samples. We also make a first assessment of substructure within our clusters. The velocity dispersions range from 400 to 1100 $\,{\rm km}\,{\rm s}^{-1}$. Some of the redshift distributions are significantly non-Gaussian and we find evidence for significant substructure in two clusters, one at $z \sim 0.79$ and the other at $z \sim 0.54$. Both have velocity dispersions exceeding 1000 $\,{\rm km}\,{\rm s}^{-1}$ but are clearly not fully virialised; their velocity dispersions may thus be a poor indicator of their masses. The properties of these first 5 EDisCS clusters span a wide range in redshift, velocity dispersion, richness and substructure, but are representative of the sample as a whole. Spectroscopy for the full dataset will allow a comprehensive study of galaxy evolution as a function of cluster environment and redshift.
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