Studying Cosmic Evolution with the XMM-Newton Distant Cluster Project

Investigating X-ray luminous galaxy clusters at high redshift (z>~1) provides a challenging but fundamental constraint on evolutionary studies of the largest virialized structures in the Universe, the baryonic matter component in form of the hot intracluster medium (ICM), their galaxy populations, and the effects of the mysterious Dark Energy. The main aim of this thesis work is to establish the observational foundation for the XMM-Newton Distant Cluster Project (XDCP). This new generation serendipitous X-ray survey is focused on the most distant galaxy clusters at z>1, based on the selection of extended X-ray sources, their identification as clusters and redshift estimation via two-band imaging, and their final spectroscopic confirmation. As a first step, I have analyzed 80 deg^2 (469 fields) of deep XMM-Newton archival X-ray data with a new pipeline processing system and selected almost 1000 extended sources as galaxy cluster candidates, 75% of which could be identified as clusters or groups at z<~0.6 using available optical data. This left about 250 candidates with typical 0.5-2.0keV X-ray fluxes of ~10^{-14} erg/s/cm^2 in need of confirmation as distant cluster sources. Therefore, I have adopted a new strategy to efficiently establish the nature of these extended X-ray sources and estimate their redshifts, based on medium deep Z- and H-band photometry and the observed Z-H `red-sequence' color of early-type cluster galaxies. To fully exploit this technique, I have designed a new near-infrared data reduction code, which was applied to the data collected for 25% of the 250 distant cluster candidates in two imaging campaigns at the 3.5m telescope at the Calar Alto Observatory. As a first main result, more than 20 X-ray luminous clusters were discovered to lie at a photometric redshift of z>~0.9. Furthermore, the new Z-H red sequence method has allowed a cluster sample study over an unprecedented redshift baseline of 0.2<~z<~1.5. From a comparison of the observed color evolution of the cluster red-sequence galaxies with model predictions, I could constrain the formation epoch of the bulk of their stellar populations as z_f=4.2+-1.1. This confirms the well-established old age of the stellar populations of early-type galaxies in clusters. The preliminary investigation of the H-band luminosity evolution of 63 brightest cluster galaxies (BCGs) over the same redshift range provides for the first time direct observational indications that the most massive cluster galaxies in the local Universe have doubled their stellar mass since z~1.5. My tentative finding that nearby BCGs have old, passively evolving stellar populations and were assembled in the last 9Gyr is in qualitative agreement with predictions from the latest numerical simulations based on the standard cold dark matter scenario of galaxy formation and evolution via hierarchical merging. The confirmation and refinement of these preliminary results will contribute to the development of a consistent picture of the cosmic evolution of galaxy populations and the large-scale structure

F-VIPGI: a new adapted version of VIPGI for FORS2 spectroscopy. Application to a sample of 16 X-ray selected galaxy clusters at 0.6 < z < 1.2

The goal of this paper is twofold. Firstly, we present F-VIPGI, a new version of the VIMOS Interactive Pipeline and Graphical Interface (VIPGI) adapted to handle FORS2 spectroscopic data. Secondly, we investigate the spectro-photometric properties of a sample of galaxies residing in distant X-ray selected galaxy clusters, the optical spectra of which were reduced with this new pipeline. We provide basic technical information about the innovations of the new software and, as a demonstration of the capabilities of the new pipeline, we show results obtained for 16 distant (0.65 < z < 1.25) X-ray luminous galaxy clusters selected within the XMM-Newton Distant Cluster Project. We performed a spectral indices analysis of the extracted optical spectra of their members, based on which we created a library of composite high signal-to-noise ratio spectra representative of passive and star-forming galaxies residing in distant galaxy clusters. The spectroscopic templates are provided to the community in electronic form. By comparing the spectro-photometric properties of our templates with the local and distant galaxy population residing in different environments, we find that passive galaxies in clusters appear to be well evolved already at z = 0.8 and even more so than the field galaxies at similar redshift. Even though these findings would point toward a significant acceleration of galaxy evolution in densest environments, we cannot exclude the importance of the mass as the main evolutionary driving element either. The latter effect may indeed be justified by the similarity of our composite passive spectrum with the luminous red galaxies template at intermediate redshift.Comment: 15 pages, 15 figures, in press on Astronomy and Astrophysic

The reversal of the SF-density relation in a massive, X-ray selected galaxy cluster at z=1.58: results from Herschel

Dusty, star-forming galaxies have a critical role in the formation and evolution of massive galaxies in the Universe. Using deep far-infrared imaging in the range 100-500um obtained with the Herschel telescope, we investigate the dust-obscured star formation in the galaxy cluster XDCP J0044.0-2033 at z=1.58, the most massive cluster at z >1.5, with a measured mass M200= 4.7x10$^{14}$ Msun. We perform an analysis of the spectral energy distributions (SEDs) of 12 cluster members (5 spectroscopically confirmed) detected with >3$\sigma$ significance in the PACS maps, all ULIRGs. The individual star formation rates (SFRs) lie in the range 155-824 Ms/yr, with dust temperatures of 24$\pm$35 K. We measure a strikingly high amount of star formation (SF) in the cluster core, SFR ( 1875$\pm$158 Ms/yr, 4x higher than the amount of star formation in the cluster outskirts. This scenario is unprecedented in a galaxy cluster, showing for the first time a reversal of the SF-density relation at z~1.6 in a massive cluster.Comment: Letter accepted for publication in MNRAS, ESA Press Release on 18 December 201

VADER - A Satellite Mission Concept For High Precision Dark Energy Studies

We present a satellite mission concept to measure the dark energy equation of state parameter w with percent-level precision. The Very Ambitious Dark Energy Research satellite (VADER) is a multi-wavelength survey mission joining X-ray, optical, and IR instruments for a simultaneous spectral coverage from 4microns (0.3eV) to 10keV over a field of view (FoV) of 1 square degree. VADER combines several clean methods for dark energy studies, the baryonic acoustic oscillations in the galaxy and galaxy cluster power spectrum and weak lensing, for a joint analysis over an unrivalled survey volume. The payload consists of two XMM-like X-ray telescopes with an effective area of 2,800cm^2 at 1.5keV and state-of-the-art wide field DEPFET pixel detectors (0.1-10keV) in a curved focal plane configuration to extend the FoV. The X-ray telescopes are complemented by a 1.5m optical/IR telescope with 8 instruments for simultaneous coverage of the same FoV from 0.3 to 4 microns. The 8 dichroic-separated bands (u,g,r,z,J,H,K,L) provide accurate photometric galaxy redshifts, whereas the diffraction-limited resolution of the central z-band allows precise shape measurements for cosmic shear analysis. The 5 year VADER survey will cover a contiguous sky area of 3,500 square degrees to a depth of z~2 and will yield accurate photometric redshifts and multi-wavelength object parameters for about 175,000 galaxy clusters, one billion galaxies, and 5 million AGN. VADER will not only provide unprecedented constraints on the nature of dark energy, but will additionally extend and trigger a multitude of cosmic evolution studies to very large (>10 Gyrs) look-back times.Comment: 14 pages, 7 figures, accepted for publication in the SPIE conference proceeding

Discovery of a massive X-ray luminous galaxy cluster at z=1.579

We report on the discovery of a very distant galaxy cluster serendipitously detected in the archive of the XMM-Newton mission, within the scope of the XMM-Newton Distant Cluster Project (XDCP). XMMUJ0044.0-2033 was detected at a high significance level (5sigma) as a compact, but significantly extended source in the X-ray data, with a soft-band flux f(r<40")=(1.5+-0.3)x10^(-14) erg/s/cm2. Optical/NIR follow-up observations confirmed the presence of an overdensity of red galaxies matching the X-ray emission. The cluster was spectroscopically confirmed to be at z=1.579 using ground-based VLT/FORS2 spectroscopy. The analysis of the I-H colour-magnitude diagram shows a sequence of red galaxies with a colour range [3.7 < I-H < 4.6] within 1' from the cluster X-ray emission peak. However, the three spectroscopic members (all with complex morphology) have significantly bluer colours relative to the observed red-sequence. In addition, two of the three cluster members have [OII] emission, indicative of on-going star formation. Using the spectroscopic redshift we estimated the X-ray bolometric luminosity, Lbol = 5.8x10^44 erg/s, implying a massive galaxy cluster. This places XMMU J0044.0-2033 at the forefront of massive distant clusters, closing the gap between lower redshift systems and recently discovered proto- and low-mass clusters at z >1.6.Comment: letter to appear in A&

The X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.56 - The dawn of starburst activity in cluster cores

Observational galaxy cluster studies at z>1.5 probe the formation of the first massive M>10^14 Msun dark matter halos, the early thermal history of the hot ICM, and the emergence of the red-sequence population of quenched early-type galaxies. We present first results for the newly discovered X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.555, detected and confirmed by the XMM-Newton Distant Cluster Project (XDCP) survey. We selected the system as a serendipitous weak extended X-ray source in XMM-Newton archival data and followed it up with two-band near-infrared imaging and deep optical spectroscopy. We can establish XMMU J1007.4+1237 as a spectroscopically confirmed, massive, bona fide galaxy cluster with a bolometric X-ray luminosity of Lx=(2.1+-0.4)\times 10^44 erg/s, a red galaxy population centered on the X-ray emission, and a central radio-loud brightest cluster galaxy. However, we see evidence for the first time that the massive end of the galaxy population and the cluster red-sequence are not yet fully in place. In particular, we find ongoing starburst activity for the third ranked galaxy close to the center and another slightly fainter object. At a lookback time of 9.4Gyr, the cluster galaxy population appears to be caught in an important evolutionary phase, prior to full star-formation quenching and mass assembly in the core region. X-ray selection techniques are an efficient means of identifying and probing the most distant clusters without any prior assumptions about their galaxy content.Comment: 6 pages, 3 color figures, accepted for publication in A&

A large-scale galaxy structure at z = 2.02 associated with the radio galaxy MRC 0156-252

We present the spectroscopic confirmation of a structure of galaxies surrounding the radio galaxy MRC 0156-252 at z = 2.02. The structure was initially discovered as an overdensity of both near-infrared selected z > 1.6 and mid-infrared selected z > 1.2 galaxy candidates. We used the VLT/FORS2 multi-object spectrograph to target ~80 high-redshift galaxy candidates, and obtain robust spectroscopic redshifts for more than half the targets. The majority of the confirmed sources are star-forming galaxies at z > 1.5. In addition to the radio galaxy, two of its close-by companions (<6″) also show AGN signatures. Ten sources, including the radio galaxy, lie within | z − 2.020 | <0.015 (i.e., velocity offsets <1500 km s^-1) and within projected 2 Mpc comoving of the radio galaxy. Additional evidence suggests not only that the galaxy structure associated with MRC 0156-252 is a forming galaxy cluster but also that this structure is most probably embedded in a larger-scale structure