M. Mühlegger

Observational constraints on the redshift evolution of X-ray scaling relations of galaxy clusters out to z ~ 1.5

Context. A precise understanding of the relations between observable X-ray properties of galaxy clusters and cluster mass is a vital part of the application of X-ray galaxy cluster surveys to te st cosmological models. An understanding of how these relations evolve with redshift is just emerging from a number of observational data sets. Aims. The current literature provides a diverse and inhomogeneous picture of scaling relation evolution. We attempt to trans form these results and the data on recently discovered distant cl usters into an updated and consistent framework, and provide an overall view of scaling relation evolution from the combined data sets. Methods. We study in particular the most important scaling relations connecting X-ray luminosity, temperature, and cluster mass (M‐ T, LX‐T, and M‐LX) combining 14 published data sets supplemented with recently published data of distant clusters and new results from follow-up observations of the XMM-Newton Distant Cluster Project (XDCP) that adds new leverage to effi ciently constrain the scaling relations at high redshift. Results. We find that the evolution of the mass-temperature relation i s consistent with the self-similar evolution prediction, w hile the evolution of X-ray luminosity for a given temperature and mass for a given X-ray luminosity is slower than predicted by simple self-similar models. Our best fit results for the evolution f actor E(z) � are �=−1.04± 0.07 for the M‐T relation, �=−0.23 +0.12 −0.62 for the L-T relation, and �=−0.93 +0.62 −0.12 for the M‐LX relation. We also explore the influence of selection e ffects on scaling relations and find that selection biases are the most likely reason for apparen t inconsistencies between different published data sets. Conclusions. The new results provide the currently most robust calibration of high-redshift cluster mass estimates based on X-ray luminosity and temperature and help us to improve the prediction of the number of clusters to be found in future galaxy cluster X-ray surveys, such as eROSITA. The comparison of evolution results with hydrodynamical cosmological simulations suggests that early preheating of the intracluster medium (ICM) provides the most suitable scenario to explain the observed evolution.

eROSITA on SRG

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max-Planck-Society. The instrument development is in phase C/D since fall 2009. The design driving science is the detection 100.000 Clusters of Galaxies up to redshift z ~1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all-sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter-I telescope modules, each equipped with 54 Wolter-I shells having an outer diameter of 360 mm. This would provide an effective area of ~1500 cm2 at 1.5 keV and an on axis PSF HEW of 15 arcsec resulting in an effective angular resolution of 28 - 30 arcsec, averaged over the field of view. In the focus of each mirror module, a fast frame-store pn-CCD provides a field of view of 1° in diameter.

First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND - The galaxy population of XMMU J0338.7 + 0030 at z = 1.1

Context. The XMM-Newton Distant Cluster Project is a serendipitous survey for clusters of galaxies at redshifts z ≥ 0.8 based on deep archival XMM-Newton observations. X-ray sources identified as extended are screened against existing optical all-sky surveys for galaxies, in case of candidate high-z clusters followed up with imaging at 4 m-class telescopes and, ultimately, multi-object spectroscopy at 8 m-class telescopes. Low-significance candidate high-z clusters are followed up with the seven-channel imager GROND (Gamma-Ray Burst Optical and Near-Infrared Detector) that is mounted at a 2 m-class telescope. Its unique capability of simultaneous imaging in the g′,r′,i′,z′,J,H,Ks bands enables the use of the photometric redshift technique. Aims. Observing strategy, data reduction and analysis, depth and accuracy of the simultaneous multi-wavelength photometry are discussed with the goal of establishing GROND as a useful instrument to confirm X-ray selected (high-z) clusters. Methods. The test case is XMMU J0338.7 + 0030, suggested to be at z ~ 1.45 ± 0.15 (1σ) from the analysis of the z − H vs. H colour − magnitude diagram obtained from the follow-up imaging. Later VLT-FORS2 spectroscopy enabled us to identify four members, which set this cluster at z = 1.097 ± 0.002 (1σ). To reach a better knowledge of its galaxy population, we observed XMMU J0338.7 + 0030 with GROND for about 6 h. The publicly available photo-z code le Phare was used. Results. The Ks-band number counts of the non-stellar sources out of the 832 detected down to z′ ~ 26 AB mag (1σ) in the 3.9 × 4.3 arcmin^2 region of XMMU J0338.7 + 0030 imaged at all GROND bands clearly exceed those computed in deep fields/survey areas at ~20.5–22.5 AB mag. The photo-z’s of the three imaged spectroscopic members yield z = 1.12 ± 0.09 (1σ). The spatial distribution and the properties of the GROND sources with a photo-z in the range 1.01–1.23 confirm the correspondence of the X-ray source with a galaxy over-density at a significance of at least 4.3σ. Candidate members that are spectro-photometrically classified as elliptical galaxies define a red locus in the i′ − z′ vs. z′ colour − magnitude diagram that is consistent with the red sequence of the cluster RDCS J0910 + 5422 at z = 1.106. XMMU J0338.7 + 0030 hosts also a population of bluer late-type spirals and irregulars. The starbursts among the photometric members populate both loci, consistently with previous results. Conclusions. The analysis of the available data set indicates that XMMU J0338.7 + 0030 is a low-mass cluster (M_200 ~ 10^(14) M_⊙) at z = 1.1. With the photometric accuracy yielded by the present unoptimized multi-band observations with GROND, we not only confirm the spectroscopic redshift of this cluster but also show that it hosts a galaxy population that can still undergo significant bursts of star-formation activity.

Exploring the galaxy cluster-group transition regime at high redshifts - physical properties of two newly detected z > 1 systems

Context: Multi-wavelength surveys for clusters of galaxies are opening a window on the elusive high-redshift (z>1) cluster population. Well controlled statistical samples of distant clusters will enable us to answer questions about their cosmological context, early assembly phases and the thermodynamical evolution of the intracluster medium. Aims: We report on the detection of two z>1 systems, XMMU J0302.2-0001 and XMMU J1532.2-0836, as part of the XMM-Newton Distant Cluster Project (XDCP) sample. We investigate the nature of the sources, measure their spectroscopic redshift and determine their basic physical parameters. Methods: The results of the present paper are based on the analysis of XMM-Newton archival data, optical/near-infrared imaging and deep optical follow-up spectroscopy of the clusters. Results: We confirm the X-ray source XMMU J0302.2-0001 as a gravitationally bound, bona fide cluster of galaxies at spectroscopic redshift z=1.185. We estimate its M500 mass to (1.6+/-0.3) times 10^{14} Msun from its measured X-ray luminosity. This ranks the cluster among intermediate mass system. In the case of XMMU J1532.2-0836 we find the X-ray detection to be coincident with a dynamically bound system of galaxies at z=1.358. Optical spectroscopy reveals the presence of a central active galactic nucleus, which can be a dominant source of the detected X-ray emission from this system. We provide upper limits of X-ray parameters for the system and discuss cluster identification challenges in the high-redshift low-mass cluster regime. A third, intermediate redshift (z=0.647) cluster, XMMU J0302.1-0000, is serendipitously detected in the same field as XMMU J0302.2-0001. We provide its analysis as well.

Simulations of X-ray telescopes for eROSITA and IXO

We report on the development of a generic X‐ray instrument simulator to be used in simulations of future X‐ray missions. Based on a Monte Carlo approach the code generates photon events for sources in an X‐ray source catalogue such as the ROSAT all sky survey or the XMM‐Newton slew surveys and then models the imaging and detection process based on the available calibration files (e.g., point spread functions for the imaging). The output of the program are event lists, which can be analysed using standard software such as xselect. Due to its modular concept the simulation software can be easily adapted to different concepts of imaging detectors.As examples for the potential use of the simulation we present our studies for eROSITA and show results of simulations of the detector performance for the High Time Resolution Spectrometer and the Wide Field Imager on the International X‐ray Observatory.

Design and development of the eROSITA x-ray mirrors

MPE will provide the X-ray Survey Telescope eROSITA [5] for the Russian Spektrum-Roentgen-Gamma Mission [4] to be launched in 2011. The design of the X-ray mirror system is based on that of ABRIXAS: The bundle of 7 mirror modules with the short focal length of 1600 mm makes it still a compact instrument while, however, its sensitivity in terms of effective area, field-of-view, and angular resolution shall be largely enhanced with respect to ABRIXAS. The number of nested mirror shells increases from 27 to 54 compared to ABRIXAS thus enhancing the effective area in the soft band by a factor of six. The angular resolution is targeted to be 15 arc seconds half-energy width (HEW) on-axis resulting in an average HEW of 26 arc seconds over the 61 arc minutes field-of-view (FoV). The instruments high grasp of about 1000 cm2deg2 in the soft spectral range and still 10 cm2deg2 at 10 keV combined with a survey duration of 4 years will generate a new rich database of X-ray sources over the whole sky. As the 7 mirror modules are co-aligned eROSITA is also able to perform pointed observations.

New technology and techniques for X-ray mirror calibration at PANTER

The PANTER X-ray Test Facility has been utilized successfully for developing and calibrating X-ray astronomical instrumentation for observatories such as ROSAT, Chandra, XMM-Newton, Swift, etc. Future missions like eROSITA, SIMBOL-X, or XEUS require improved spatial resolution and broader energy band pass, both for optics and for cameras. Calibration campaigns at PANTER have made use of flight spare instrumentation for space applications; here we report on a new dedicated CCD camera for on-ground calibration, called TRoPIC. As the CCD is similar to ones used for eROSITA (pn-type, back-illuminated, 75 μm pixel size, frame store mode, 450 μm micron wafer thickness, etc.) it can serve as prototype for eROSITA camera development. New techniques enable and enhance the analysis of measurements of eROSITA shells or silicon pore optics. Specifically, we show how sub-pixel resolution can be utilized to improve spatial resolution and subsequently the characterization of of mirror shell quality and of point spread function parameters in particular, also relevant for position reconstruction of astronomical sources in orbit.