arXiv subjects

Rene Fassbender

Publications and source records attributed to Rene Fassbender.

13 recordsLinked to original sources

arXiv2021

The HST See Change Program: I. Survey Design, Pipeline, and Supernova Discoveries

The See Change survey was designed to make $z>1$ cosmological measurements by efficiently discovering high-redshift Type Ia supernovae (SNe Ia) and improving cluster mass measurements through weak lensing. This survey observed twelve galaxy clusters with the Hubble Space Telescope spanning the redshift range $z=1.13$ to $1.75$, discovering 57 likely transients and 27 likely SNe Ia at $z\sim 0.8-2.3$. As in similar previous surveys (Dawson et al. 2009), this proved to be a highly efficient use of HST for SN observations; the See Change survey additionally tested the feasibility of maintaining, or further increasing, the efficiency at yet higher redshifts, where we have less detailed information on the expected cluster masses and star-formation rates. We find that the resulting number of SNe Ia per orbit is a factor of $\sim 8$ higher than for a field search, and 45% of our orbits contained an active SN Ia within 22 rest-frame days of peak, with one of the clusters by itself yielding 6 of the SNe Ia. We present the survey design, pipeline, and SN discoveries. Novel features include fully blinded SN searches, the first random forest candidate classifier for undersampled IR data (with a 50% detection threshold within 0.05 magnitudes of human searchers), real-time forward-modeling photometry of candidates, and semi-automated photometric classifications and follow-up forecasts. We also describe the spectroscopic follow-up, instrumental in measuring host-galaxy redshifts. The cosmology analysis of our sample will be presented in a companion paper.

astro-ph.CO↗

arXiv2014

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$σ$ 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$35 K. We measure a strikingly high amount of star formation (SF) in the cluster core, SFR (< 250 kpc) > 1875$\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.

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arXiv2014

Kinematic analysis of a sample of X-ray luminous distant galaxy clusters. The $L_X$ - $σ_v$ relation in the $z>0.6$ universe

Observations and cosmological simulations show galaxy clusters as a family of nearly self-similar objects with properties that can be described by scaling relations as a function of e.g. mass and time. Here we study the scaling relations between the galaxy velocity dispersion and X-ray quantities like X-ray bolometric luminosity and temperature in galaxy clusters at high redshifts (0.64 $\leq$ z $\leq$ 1.46). We also compare our results with the similar study of the local HIFLUGCS sample. For the analysis, we use a set of 15 distant galaxy clusters extracted from the literature plus a sample of 10 newly discovered clusters selected in X-rays by the \XMM Distant Cluster Project (XDCP) with more than 10 confirmed spectroscopic members per cluster. We also study the evolution of this scaling relation by comparing the high redshift results with the data from the local HIFLUGCS sample. We also investigated the $L_X - T_X$ and the $σ_v - T_X$ relations for the 15 clusters in the literature sample. We report the results of the X-ray and kinematic analysis of 10 newly detected high redshift clusters and provide their spectroscopic and kinematic details. For the entire, distant sample we find a slope fully consistent with the one typical of local clusters, albeit with a large associated uncertainty. The study on the evolution of the amplitude reveals a positive offset if the self-similar evolution is neglected, hence possibly indicating the need for including evolutionary effects. However, the $L_X - T_X$ relation is found to be in good agreement with the local relation without any significant redshift evolution. Finally, the $σ_v - T_X$ relation appears to slightly deviate from the theoretical expectation that galaxies and gas particles have a similar specific kinetic energy. However, the associated uncertainty is currently too large for making any conclusive statement in this regard.

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arXiv2013

A large-scale galaxy structure at z = 2.02 associated with the radio galaxy MRC0156-252

We present the spectroscopic confirmation of a structure of galaxies surrounding the radio galaxy MRC0156-252 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) and within projected 2 Mpc comoving of the radio galaxy. Additional evidence suggests not only that the galaxy structure associated with MRC0156-252 is a forming galaxy cluster but also that this structure is most probably embedded in a larger scale structure.

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arXiv2013

Distant galaxy clusters in a deep XMM-Newton field within the CFTHLS D4

The XMM-Newton Distant Cluster Project (XDCP) aims at the identification of a well defined sample of X-ray selected clusters of galaxies at redshifts z>0.8. We present a catalogue of the extended sources in one the deepest ~250 ksec XMM-Newton fields targeting LBQS 2215-175 covering the CFHTLS deep field four. The cluster identification is based, among others, on deep imaging with the ESO VLT and from the CFHT legacy survey. The confirmation of cluster candidates is done by VLT/FORS2 multi-object spectroscopy. Photometric redshifts from the CFHTLS D4 are utilized to confirm the effectiveness of the X-ray cluster selection method. The survey sensitivity is computed with extensive simulations. At a flux limit of S(0.5-2.0 keV) ~ 2.5e-15 erg/s we achieve a completeness level higher than 50% in an area of ~0.13 square degrees. We detect six galaxy clusters above this limit with optical counterparts, of which 5 are new spectroscopic discoveries. Two newly discovered X-ray luminous galaxy clusters are at z>1.0, another two at z=0.41 and one at z=0.34. For the most distant X-ray selected cluster in this field at z=1.45 we find additional (active) member galaxies from both X-ray and spectroscopic data. Additionally, we find evidence of large scale structures at moderate redshifts of z=0.41 and z=0.34. The quest for distant clusters in archival XMM-Newton data has led to the detection of six clusters in a single field, making XMM-Newton an outstanding tool for cluster surveys. Three of these clusters are at z>1, which emphasises the valuable contribution of small, yet deep surveys to cosmology. Beta-models are appropriate descriptions for the cluster surface brightness to perform cluster detection simulations in order to compute the X-ray selection function. The constructed logN-logS tends to favour a scenario where no evolution in the cluster X-ray luminosity function (XLF) takes place.

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arXiv2013

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.

astro-ph.IM↗

arXiv2011

Discovery of the X-ray selected galaxy cluster XMMU J0338.8+0021 at z = 1.49 - Indications for a young system with a forming brightest galaxy

We report on the discovery of a galaxy cluster at z = 1.490 originally selected as an extended X-ray source in the XMM-Newton Distant Cluster Project. Further observations carried out with the VLT-FORS2 spectrograph allowed the spectroscopic confirmation of seven secure cluster members, providing a median system redshift of z = 1.490 +/- 0.009. The color magnitude diagram of XMMU J0338.8+0021 reveals the presence of a well populated red sequence with z-H ~ 3, albeit with an apparent significant scatter in color. Since we do not detect indications for strong star formation activity in any of the objects, the color spread could indicate different stellar ages of the member galaxies. In addition, we found the brightest cluster galaxy in a very active dynamical state, with an interacting, merging companion located at a physical projected distance of d ~ 20kpc. From the X-ray luminosity we estimate a cluster mass of M200 ~ 1.2 x 10^(14) Msun. The data seem to suggest a scenario in which XMMU J0338.8+0021 is a young system, possibly caught in a moment of active ongoing mass assembly.

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arXiv2011

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.

astro-ph.CO↗

arXiv2011

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.

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arXiv2010

A pan-chromatic view of the galaxy cluster XMMU J1230.3+1339 at z=0.975 - Observing the assembly of a massive system

We present a comprehensive galaxy cluster study of XMMU J1230.3+1339 based on a joint analysis of X-ray data, optical imaging and spectroscopy observations, weak lensing results, and radio properties for achieving a detailed multi-component view of this newly discovered system at z=0.975. We find an optically very rich and massive system with M200$\simeq$(4.2$\pm$0.8)$\times$10^14 M$\sun$, Tx$\simeq$5.3(+0.7--0.6)keV, and Lx$\simeq$(6.5$\pm$0.7)$\times$10^44 erg/s, for which various widely used mass proxies are measured and compared. We have identified multiple cluster-related components including a central fly-through group close to core passage with associated marginally extended 1.4GHz radio emission possibly originating from the turbulent wake region of the merging event. On the cluster outskirts we see evidence for an on-axis infalling group with a second Brightest Cluster Galaxy (BCG) and indications for an additional off-axis group accretion event. We trace two galaxy filaments beyond the nominal cluster radius and provide a tentative reconstruction of the 3D-accretion geometry of the system. In terms of total mass, ICM structure, optical richness, and the presence of two dominant BCG-type galaxies, the newly confirmed cluster XMMU J1230.3+1339 is likely the progenitor of a system very similar to the local Coma cluster, differing by 7.6 Gyr of structure evolution.

astro-ph.CO↗

arXiv2009

Multi-wavelength observations of a rich galaxy cluster at z ~ 1: the HST/ACS colour-magnitude diagram

XMMU J1229+0151 is a rich galaxy cluster with redshift z=0.975, that was serendipitously detected in X-rays within the scope of the XMM-Newton Distant Cluster Project. HST/ACS observations in the i775 and z850 passbands, as well as VLT/FORS2 spectroscopy were further obtained, in addition to follow-up Near-Infrared (NIR) imaging in J- and Ks-bands with NTT/SOFI. We investigate the photometric, structural and spectral properties of the early-type galaxies in the high-redshift cluster XMMU J1229+0151. Source detection and aperture photometry are performed in the optical and NIR imaging. Galaxy morphology is inspected visually and by means of Sersic profile fitting to the 21 spectroscopically confirmed cluster members in the ACS field of view. The i775-z850 colour-magnitude relation (CMR) is derived with a method based on galaxy magnitudes obtained by fitting the surface brightness of the galaxies with Sersic models. The i775-z850 CMR of the spectroscopic members shows a very tight red-sequence with a zero point of 0.86+-0.04 mag and intrinsic scatter equal to 0.039 mag. The CMR obtained with the galaxy models has similar parameters. Stellar masses and formation ages of the cluster galaxies are derived by fitting the observed spectral energy distributions (SED) with models based on Bruzual & Charlot 2003. We obtain a star formation weighted age of 4.3 Gyr for a median mass of 7.4e10 Msun. Instead of an unambiguous brightest cluster galaxy (BCG), we find three bright galaxies with a similar z850 magnitude, which are, in addition, the most massive cluster members, with ~ 2e11 Msun. Our results strengthen the current evidence for a lack of significant evolution of the scatter and slope of the red-sequence out to z~1.

astro-ph.CO↗

arXiv2008

Studying Cosmic Evolution with the XMM-Newton Distant Cluster Project: X-ray Luminous Galaxy Clusters at z>~1 and their Galaxy Populations

Investigating X-ray luminous galaxy clusters at z>~1 provides a fundamental constraint on evolutionary studies of the largest virialized structures in the Universe, the baryonic matter in form of the hot ICM, their galaxy populations, and the effects of Dark Energy. The main aim of this work is to establish the observational foundation for the XMM-Newton Distant Cluster Project (XDCP). This new serendipitous survey is focused on the most distant systems at z>1, based on the selection of extended X-ray sources, their identification as clusters via two-band imaging, and their final spectroscopic confirmation. Almost 1000 extended sources were selected as cluster candidates from the analysis of 80 deg^2 of deep XMM-Newton archival data, of which 75% could be readily identified as systems at z<~0.6. For the remaining 250 distant cluster candidates a new strategy for their confirmation and redshift estimates was adopted, based on Z- and H-band photometry and the observed Z-H red-sequence color of early-type cluster galaxies. From observations of 25% of the sample, more than 20 X-ray clusters were discovered at a photometric redshift of z>~0.9. The new Z-H 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 red-sequence with model predictions, the formation epoch of early-type galaxies could be constrained as z_f=4.2+-1.1, confirming their well-established old age. The preliminary investigation of the H-band luminosity evolution of 63 BCGs provides for the first time direct observational indications that the most massive cluster galaxies have doubled their stellar mass since z~1.5. The finding that BCGs were assembled in the last 9Gyr is now in qualitative agreement with the latest simulations.

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arXiv2006

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.

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