arXiv subjects

Oliver Czoske

Publications and source records attributed to Oliver Czoske.

28 records · Page 2Linked to original sources

arXiv2004

Wide-field spectroscopy of A1689 and A1835 with VIMOS: First results

We are using VIMOS to conduct a wide-field spectroscopic survey covering fields of 0.5 x 0.5 sqdeg around the X-ray luminous clusters of galaxies Abell 1689 (z = 0.185) and Abell 1835 (z = 0.25). Here we describe the observations and first results on the redshift distribution of subsamples of cluster galaxies to R~22 for which we at present have obtained secure redshifts. These subsamples constitute ~40% of the total spectroscopic sample and contain 525 and 630 cluster members in Abell 1689 and Abell 1835, respectively, placing them amongst the largest redshift samples available for any cluster of galaxies.

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arXiv2004

A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy Clusters: IV. Mass, Structure and Thermodynamics of Cluster Cores at z=0.2

We present a comprehensive space-based study of ten X-ray luminous galaxy clusters (L_X>=8e44erg/s[0.1-2.4keV]) at z=0.2. Hubble Space Telescope observations reveal numerous gravitationally-lensed arcs for which we present four new spectroscopic redshifts, bringing the total to thirteen confirmed arcs in this cluster sample. We combine the multiple-image systems with the weakly-sheared background galaxies to model the total mass distribution in the cluster cores (R<=500kpc). These models are complemented by high-resolution X-ray data from Chandra and used to develop quantitative criteria to classify the clusters as relaxed or unrelaxed. Formally, (30+/-20)% of the clusters form a homogeneous sub-sample of relaxed clusters; the remaining (70+/-20)% are unrelaxed and are a much more diverse population. Most of the clusters therefore appear to be experiencing a cluster-cluster merger, or relaxing after such an event. We also study the normalization and scatter of scaling relations between cluster mass, luminosity and temperature. The scatter in these relations is dominated by the unrelaxed clusters and is typically sigma~0.4. Most notably, we detect 2-3 times more scatter in the mass-temperature relation than theoretical simulations and models predict. The observed scatter is also asymmetric - the unrelaxed systems are systematically 40% hotter than the relaxed clusters at 2.5 sigma significance. This structural segregation should be a major concern for experiments designed to constrain cosmological parameters using galaxy clusters. Overall our results are consistent with a scenario of cluster-cluster merger induced boosts to cluster X-ray luminosities and temperatures. [Abridged]

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arXiv2003

A Wide Field Hubble Space Telescope Study of the Cluster Cl0024+1654 at z=0.4 II: The Cluster Mass Distribution

(abridged) We present a comprehensive lensing analysis of the rich cluster Cl0024+1654 based on panoramic sparse-sampled imaging conducted with HST. We demonstrate an ability to detect reliably weak lensing signals to a cluster radius of ~5 Mpc where the mean shear is around 1%. The projected mass distribution reveals a secondary concentration representing 30% of the overall cluster mass, which is also visible in the distribution of cluster member galaxies. We normalize the mass profile determined from the shear by assuming that background galaxies selected with I=23-26 have a redshift distribution statistically similar to that in the HDFs. Combining strong and weak constraints, we are able to probe the mass profile of the cluster on scales of 0.1 to 5 Mpc thus providing a valuable test of the universal form proposed by NFW on large scales. A generalized power law fit indicates a asymptotic density distribution with 3D slope larger than 2.4. An isothermal mass profile is therefore strongly rejected, whereas a NFW profile with M_200= 6.1+/-1 10^14 M_sun provides a good fit to the lensing data. We isolate cluster members according to their optical-near infrared colors; the red cluster light closely traces the dark matter with a mean mass-to-light ratio of M/L_K~ 40 M/L_sun. Similar profiles for mass and light on 1-5 Mpc scales are expected if cluster assembly is largely governed by infalling groups.

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arXiv2002

The Most Massive Clusters in the Universe

Clusters of galaxies need to be investigated using complementary approaches combining all currently available observational techniques (X-ray, gravitational lensing, dynamics, SZ) on homogeneous samples if one wants to understand their evolution and physical properties. This is particularly important in order to relate the observable quantities to the cosmologically important cluster mass. We present here a number of on-going projects that aim at studying cluster physics for samples based on currently available all-sky X-ray surveys such as XBACs, BCS and MACS.

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arXiv2002

A wide-field spectroscopic survey of the cluster of galaxies Cl0024+1654. II. A high-speed collision?

The mass distribution of the rich cluster of galaxies Cl0024+1654 has frequently been used to constrain the nature of dark matter yet a model consistent with all the observational data has been difficult to construct. In this paper we analyse the three-dimensional structure of this cluster using new spectroscopic information on ~300 galaxies within a projected radius of 3 Mpc/h. These data reveal an unusual foreground component of galaxies separated from the main cluster by 3000 km/s. We use numerical simulations to show that a high speed collision along the line of sight between Cl0024+1654 and a second cluster of slightly smaller mass can reproduce the observed peculiar redshift distribution. The collision dramatically alters the internal mass distribution of the bound remnants, creating constant density cores from initially cuspy dark matter profiles and scattering galaxies to large projected radii. Our results can reconcile the inferred mass profile from gravitational lensing with predictions from hierarchical structure formation models, while at the same time resolving the mass discrepancy that results from a comparison between lensing, velocity dispersion and X-ray studies.

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arXiv2001

A Hubble Space Telescope Lensing Survey of X-ray Luminous Galaxy Clusters: II. A Search for Gravitationally Lensed EROs

We present the results of a survey for Extremely Red Objects (EROs) in the fields of ten galaxy cluster lenses at z~0.2, combining high-resolution Hubble Space Telescope imaging with deep K-band imaging from UKIRT. We detect 60 EROs with R-K>=5.3, of which 26 have R-K>=6.0 in a total image plane survey area of 49arcmin^2 down to K=20.6. We use detailed models of the cluster lenses to quantify the lens amplification and thus correct the observed number counts and survey area for the effects of gravitational lensing. After making these corrections, we estimate surface densities at K<=21.6 of 2.5+/-0.4 and 1.2+/-0.3 arcmin^-2 for EROs with R-K>=5.3 and 6.0 respectively. These ERO number counts agree with previous shallower surveys at K<~19 and flatten significantly at magnitudes fainter than K~19-20. This flattening may be due to a transition from an ERO population dominated by evolved galaxies at z~1-2 (K<~19.5) to one dominated by dusty starburst galaxies at z>1 (K>~19.5). We also compare our results with various model predictions, including a model that attempts to explain EROs in terms of a single population of elliptical galaxies formed at high redshift. We find that a formation epoch of z_f~2.5 for this population matches the observed surface density of R-K>=5.3 EROs quite well, and the R-K>=6.0 sample less well. More sophisticated models, including semi-analytic prescriptions, under-predict the ERO surface density by approximately an order of magnitude, suggesting that these models produce insufficient stars and/or dust at high redshift.

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arXiv2001

A wide-field spectroscopic survey of the cluster of galaxies Cl0024+1654: I. The catalogue

We present the catalogue of a wide-field CFHT/WHT spectroscopic survey of the lensing cluster Cl0024+1654 at z=0.395. This catalogue contains 618 new spectra, of which 581 have identified redshifts. Adding redshifts available from the literature, the final catalogue contains data for 687 objects with redshifts identified for 650 of them. 295 galaxies have redshifts in the range 0.37<z<0.41, i. e. are cluster members or lie in the immediate neighbourhood of the cluster. The area covered by the survey is 21x25 arcmin2 in size, corresponding to 4x4.8 h^-2 Mpc2 at the cluster redshift. The survey is 45% complete down to V=22 over the whole field covered; within 3 arcmin of the cluster centre the completeness exceeds 80% at the same magnitude. A detailed completeness analysis is presented. The catalogue gives astrometric position, redshift, V magnitude and V-I colour, as well as the equivalent widths for a number of lines. Apart from the cluster Cl0024+1654 itself, three other structures are identified in redshift space: a group of galaxies at z=0.38, just in front of Cl0024+1654 and probably interacting with it, a close pair of groups of galaxies at z~0.495 and an overdensity of galaxies at z~0.18 with no obvious centre. The spectroscopic catalogue will be used to trace the three-dimensional structure of the cluster Cl0024+1654 as well as study the physical properties of the galaxies in the cluster and in its environment.

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arXiv2000

An HST Lensing Survey of X-ray Luminous Galaxy Clusters: I. A383

We analyse the mass distribution in the core of A383 (z=0.188), one of 12 X-ray luminous clusters at z~0.2 selected for a comprehensive and unbiased study of the mass distribution in massive clusters. Deep HST imaging reveals a wide variety of gravitationally lensed features in A383, including a giant arc formed from the strongly-lensed images of 2 background galaxies, 2 radial arcs, several multiply-imaged arcs and numerous arclets. Based upon the constraints from the various lensed features, we construct a detailed mass model for the central regions of the cluster, taking into account both the cluster-scale potential and perturbations from individual cluster galaxies. Keck spectroscopy of one component of the giant arc identifies it as a star-forming galaxy at z=1.01 and provides an accurate measurement of the cluster mass within the radius of the giant arc (65kpc) of (3.5+/-0.1)*10^13 Mo. Using the weak shear measured from our HST observations we extend our mass model to determine a mass of (1.8+/-0.2)*10^14 Mo within a radius of 250kpc. On smaller scales we employ the radial arcs as probes of the shape of the mass distribution in the cluster core (r<20kpc), and find that the mass profile is more peaked than a single NFW profile. The optical and X-ray properties of A383 indicate the presence of a central cooling flow, for which we derive a mass deposition rate of >200 Mo/yr. We also use the X-ray emission from A383 to obtain independent estimates of the total mass within projected radii of 65 and 250kpc: (4.0+/-1.4)*10^13 Mo and (1.2+/-0.5)*10^14 Mo, which are consistent with the lensing measurements. [Abridged]

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arXiv2000

A combined HST/CFH12k/XMM survey of X-ray luminous clusters of galaxies at z~0.2

We describe a project to study a sample of X-ray luminous clusters of galaxies at redshift z~0.2 at several scales (with HST/WFPC2 and CFHT/CFH12k) and wavebands (optical and X-ray). The main aims of the project are (i) to determine the mass profiles of the clusters on scales ranging from ~10 kpc/h to >1.5 Mpc/h using weak and strong lensing, thereby testing theoretical predictions of a ``universal mass profile'', and (ii) to calibrate the M_tot - T_X relation in view of future application in the study of the evolution of the cluster mass function at higher redshift.

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arXiv1999

A Wide-Field Spectroscopic Survey In The Cluster Lens Cl0024+17

We present a detailed velocity histogram from a wide-field spectroscopic survey in the field of the cluster lens Cl0024 showing an unrelaxed foreground structure in addition to the relaxed main cluster. This finding reduces the velocity dispersion of the main cluster compared to previous studies by a factor of about 2 and thus resolves the discrepancy between previous mass estimates for this cluster.

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