Matthias Bartelmann

Universität Heidelberg, Heidelburg, Baden-Württemberg, Germany

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Publications (244)915.15 Total impact

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    ABSTRACT: Do current observational data confirm the assumptions of the cosmological principle, or is there statistical evidence for deviations from spatial homogeneity on large scales? To address these questions, we developed a flexible framework based on spherically symmetric, but radially inhomogeneous Lemaitre-Tolman-Bondi (LTB) models with synchronous Big Bang. We expanded the (local) matter density profile in terms of flexible interpolation schemes and orthonormal polynomials. A Monte Carlo technique in combination with recent observational data was used to systematically vary the shape of these profiles. In the first part of this article, we reconsider giant LTB voids without dark energy to investigate whether extremely fine-tuned mass profiles can reconcile these models with current data. While the local Hubble rate and supernovae can easily be fitted without dark energy, however, model-independent constraints from the Planck 2013 data require an unrealistically low local Hubble rate, which is strongly inconsistent with the observed value; this result agrees well with previous studies. In the second part, we explain why it seems natural to extend our framework by a non-zero cosmological constant, which then allows us to perform general tests of the cosmological principle. Moreover, these extended models facilitate explorating whether fluctuations in the local matter density profile might potentially alleviate the tension between local and global measurements of the Hubble rate, as derived from Cepheid-calibrated type Ia supernovae and CMB experiments, respectively. We show that current data provide no evidence for deviations from spatial homogeneity on large scales. More accurate constraints are required to ultimately confirm the validity of the cosmological principle, however.
    08/2014;
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    ABSTRACT: We aim at constraining the assembly history of clusters by studying the intra cluster light (ICL) properties, estimating its contribution to the fraction of baryons in stars, f*, and understanding possible systematics/bias using different ICL detection techniques. We developed an automated method, GALtoICL, based on the software GALAPAGOS to obtain a refined version of typical BCG+ICL maps. We applied this method to our test case MACS J1206.2-0847, a massive cluster located at z=0.44, that is part of the CLASH sample. Using deep multi-band SUBARU images, we extracted the surface brightness (SB) profile of the BCG+ICL and we studied the ICL morphology, color, and contribution to f* out to R500. We repeated the same analysis using a different definition of the ICL, SBlimit method, i.e. a SB cut-off level, to compare the results. The most peculiar feature of the ICL in MACS1206 is its asymmetric radial distribution, with an excess in the SE direction and extending towards the 2nd brightest cluster galaxy which is a Post Starburst galaxy. This suggests an interaction between the BCG and this galaxy that dates back to t <= 1.5 Gyr. The BCG+ICL stellar content is 8% of M_(*,500) and the (de-) projected baryon fraction in stars is f*=0.0177 (0.0116), in excellent agreement with recent results. The SBlimit method provides systematically higher ICL fractions and this effect is larger at lower SB limits. This is due to the light from the outer envelopes of member galaxies that contaminate the ICL. Though more time consuming, the GALtoICL method provides safer ICL detections that are almost free of this contamination. This is one of the few ICL study at redshift z > 0.3. At completion, the CLASH/VLT program will allow us to extend this analysis to a statistically significant cluster sample spanning a wide redshift range: 0.2<z<0.6.
    Astronomy and Astrophysics 05/2014; 565(A126). · 5.08 Impact Factor
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    ABSTRACT: We present a new determination of the concentration-mass relation for galaxy clusters based on our comprehensive lensing analysis of 19 X-ray selected galaxy clusters from the Cluster Lensing and Supernova Survey with Hubble (CLASH). Our sample spans a redshift range between 0.19 and 0.89. We combine weak lensing constraints from the Hubble Space Telescope (HST) and from ground-based wide field data with strong lensing constraints from HST. The result are reconstructions of the surface-mass density for all CLASH clusters on multi-scale grids. Our derivation of NFW parameters yields virial masses between 0.53 x 10^15 and 1.76 x 10^15 M_sol/h and the halo concentrations are distributed around c_200c ~ 3.7 with a 1-sigma significant negative trend with cluster mass. We find an excellent 4% agreement between our measured concentrations and the expectation from numerical simulations after accounting for the CLASH selection function based on X-ray morphology. The simulations are analyzed in 2D to account for possible biases in the lensing reconstructions due to projection effects. The theoretical concentration-mass (c-M) relation from our X-ray selected set of simulated clusters and the c-M relation derived directly from the CLASH data agree at the 90% confidence level.
    04/2014;
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    ABSTRACT: We present the results of a numerical study based on the analysis of the MUSIC-2 simulations, aimed at estimating the expected concentration-mass relation for the CLASH cluster sample. We study nearly 1400 halos simulated at high spatial and mass resolution, which were projected along many lines-of-sight each. We study the shape of both their density and surface-density profiles and fit them with a variety of radial functions, including the Navarro-Frenk-White, the generalised Navarro-Frenk-White, and the Einasto density profiles. We derive concentrations and masses from these fits and investigate their distributions as a function of redshift and halo relaxation. We use the X-ray image simulator X-MAS to produce simulated Chandra observations of the halos and we use them to identify objects resembling the X-ray morphologies and masses of the clusters in the CLASH X-ray selected sample. We also derive a concentration-mass relation for strong-lensing clusters. We find that the sample of simulated halos which resemble the X-ray morphology of the CLASH clusters is composed mainly by relaxed halos, but it also contains a significant fraction of un-relaxed systems. For such a sample we measure an average 2D concentration which is ~11% higher than found for the full sample of simulated halos. After accounting for projection and selection effects, the average NFW concentrations of CLASH clusters are expected to be intermediate between those predicted in 3D for relaxed and super-relaxed halos. Matching the simulations to the individual CLASH clusters on the basis of the X-ray morphology, we expect that the NFW concentrations recovered from the lensing analysis of the CLASH clusters are in the range [3-6], with an average value of 3.87 and a standard deviation of 0.61. Simulated halos with X-ray morphologies similar to those of the CLASH clusters are affected by a modest orientation bias.
    04/2014;
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    ABSTRACT: The Einstein radius (ER) of a gravitational lens encodes information about decisive quantities such as halo mass, concentration, triaxiality, and orientation with respect to the observer. Thus, the largest Einstein radii can potentially be utilised to test the predictions of the LCDM model. Hitherto, studies have focussed on the single largest observed ER. We extend those studies by employing order statistics to formulate exclusion criteria based on the n largest Einstein radii and apply these criteria to the strong lensing analysis of 12 MACS clusters at z>0.5. We obtain the order statistics of Einstein radii by a MC approach, based on the semi-analytic modelling of the halo population on the past lightcone. After sampling the order statistics, we fit a GEV distribution to the first-order distribution, which allows us to derive analytic relations for the order statistics of the Einstein radii. We find that the Einstein radii of the 12 MACS clusters are not in conflict with the LCDM expectations. Our exclusion criteria indicate that, in order to exhibit tension with the concordance model, one would need to observe approximately twenty Einstein radii >30", ten >35" or five >42" in the range of 0.5<z<1.0 on the full sky. Furthermore, we find that, with increasing order, the haloes with the largest Einstein radii are on average less aligned along the line-of-sight and less triaxial. In general, the cumulative distribution functions steepen for higher orders, giving them better constraining power. (abridged)
    03/2014;
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    ABSTRACT: We present a strong lensing system in which a double source is imaged 5 times by 2 early-type galaxies. We take advantage in this target of the multi-band photometry obtained as part of the CLASH program, complemented by the spectroscopic data of the VLT/VIMOS and FORS2 follow-up campaign. We use a photometric redshift of 3.7 for the source and confirm spectroscopically the membership of the 2 lenses to the galaxy cluster MACS J1206.2-0847 at redshift 0.44. We exploit the excellent angular resolution of the HST/ACS images to model the 2 lenses in terms of singular isothermal sphere profiles and derive robust effective velocity dispersions of (97 +/- 3) and (240 +/- 6) km/s. The total mass distribution of the cluster is also well characterized by using only the local information contained in this lensing system, that is located at a projected distance of more than 300 kpc from the cluster luminosity center. According to our best-fitting lensing and composite stellar population models, the source is magnified by a total factor of 50 and has a luminous mass of about (1.0 +/- 0.5) x 10^{9} M_{Sun}. By combining the total and luminous mass estimates of the 2 lenses, we measure luminous over total mass fractions projected within the effective radii of 0.51 +/- 0.21 and 0.80 +/- 0.32. With these lenses we can extend the analysis of the mass properties of lens early-type galaxies by factors that are about 2 and 3 times smaller than previously done with regard to, respectively, velocity dispersion and luminous mass. The comparison of the total and luminous quantities of our lenses with those of astrophysical objects with different physical scales reveals the potential of studies of this kind for investigating the internal structure of galaxies. These studies, made possible thanks to the CLASH survey, will allow us to go beyond the current limits posed by the available lens samples in the field.
    03/2014;
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    ABSTRACT: A pressureless scenario for the Dark Matter (DM) fluid is a widely adopted hypothesis, despite the absence of a direct observational evidence. According to general relativity, the total mass-energy content of a system shapes the gravitational potential well, but different test particles perceive this potential in different ways depending on their properties. Cluster galaxy velocities, being $\ll$c, depend solely on the gravitational potential, whereas photon trajectories reflect the contributions from the gravitational potential plus a relativistic-pressure term that depends on the cluster mass. We exploit this phenomenon to constrain the Equation of State (EoS) parameter of the fluid, primarily DM, contained in galaxy clusters. We use the complementary information provided by the kinematic and lensing mass profiles of the galaxy cluster MACS 1206.2-0847 at $z=0.44$, as obtained in an extensive imaging and spectroscopic campaign within the CLASH survey. The unprecedented high quality of our data-set and the properties of this cluster are well suited to determine the EoS parameter of the cluster fluid. Since baryons contribute at most $15\%$ to the total mass in clusters and their pressure is negligible, the EoS parameter we derive describes the behavior of the DM fluid. We obtain the most stringent constraint on the DM EoS parameter to date, $w=(p_r+2\,p_t)/(3\,c^2\rho)=0.00\pm0.15\mathrm{(stat)}\pm0.08\mathrm{(syst)}$, averaged over the radial range $0.5\,\mathrm{Mpc}\leq$$r$$\leq$$r_{200}$, where $p_r$ and $p_t$ are the radial and tangential pressure, and $\rho$ is the density. We plan to further improve our constraint by applying the same procedure to all clusters from the ongoing CLASH-VLT program.
    01/2014;
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    ABSTRACT: We report observations of three gravitationally lensed supernovae (SNe) in the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program. These objects, SN CLO12Car (z = 1.28), SN CLN12Did (z = 0.85), and SN CLA11Tib (z = 1.14), are located behind three different clusters, MACSJ1720.2+3536 (z = 0.391), RXJ1532.9+3021 (z = 0.345), and Abell 383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope (HST) optical and infrared images. Based on photometric classification, we find that SNe CLO12Car and CLN12Did are likely to be Type Ia supernovae (SNe Ia), while SN CLA11Tib is probably a core-collapse SN. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was approximately 1.0 +/- 0.2 mag brighter than field SNe Ia at a similar redshift and ascribe this to gravitational lens magnification. Similarly, SN CLN12Did is approximately 0.2 +/- 0.2 mag brighter than field SNe Ia. We derive independent estimates of the predicted magnification from CLASH strong+weak lensing maps of the clusters: 0.83 +/- 0.16 mag for SN CLO12Car, 0.28 +/- 0.08 mag for SN CLN12Did, and 0.43 +/- 0.11 mag for SN CLA11Tib. The two SNe Ia provide a new test of the cluster lens model predictions: we find that the magnifications based on the SN Ia brightness and those predicted by the lens maps are consistent. Our results herald the promise of future observations of samples of cluster-lensed SNe Ia (from the ground or space) to help illuminate the dark-matter distribution in clusters of galaxies, through the direct determination of absolute magnifications.
    12/2013;
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    ABSTRACT: We present the first all-sky sample of galaxy clusters detected blindly by the Planck satellite through the Sunyaev-Zeldovich (SZ) effect from its six highest frequencies. This Early SZ (ESZ) sample of 189 candidates comprises high signal-to-noise clusters, from 6 to 29. Its high reliability (purity above 95%) is further insured by an extensive validation process based on Planck-internal quality assessments and external cross-identification and follow-up observations. Planck provides the first measured SZ signal for about 80% of the 169 ESZ known clusters. Planck further releases 30 new cluster candidates among which 20 are within the ESZ signal-to-noise selection criterion. Eleven of these 20 ESZ candidates are confirmed using XMM-Newton snapshot observations as new clusters, most of them with disturbed morphologies and low luminosities. The ESZ clusters are mostly at moderate redshifts (86% with z below 0.3) and span over a decade in mass, up to the rarest and most massive clusters with masses above 10^15 Msol.
    11/2013;
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    ABSTRACT: We present the XMM-Newton follow-up for validation of Planck cluster candidates. Twenty-five candidates have been observed to date using snapshot (~10 ksec) exposures: ten as part of a pilot programme to sample a low range of signal-to-noise ratios (45 candidates. The sensitivity and spatial resolution of XMM-Newton allows unambiguous discrimination between clusters and false candidates. A total of 21 candidates are confirmed as extended X-ray sources. Seventeen are single clusters, the majority of which are found to have highly irregular and disturbed morphologies. The remaining four sources are multiple systems, including the unexpected discovery of a supercluster at z=0.45. For most of the sources we are able to derive a redshift estimate from the X-ray Fe K line (albeit of variable quality). The new clusters span the redshift range 0.09 <~ z <~ 0.54 with a median redshift of z ~ 0.37. A first estimate is made of their X-ray properties including the characteristic size, which is used to improve the SZ Compton parameter estimate. The validation programme has helped to optimise the Planck candidate selection process. It has also provided a preview of the X-ray properties of these newly-discovered clusters, allowing comparison to their SZ properties, and to the X-ray and SZ properties of known clusters observed in the Planck survey. Our results suggest that Planck may have started to reveal a non-negligible population of massive dynamically perturbed objects that is under-represented in X-ray surveys. However, despite their particular properties, these new clusters appear to follow the Ysz-Yx relation established for X-ray selected objects.
    11/2013;
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    ABSTRACT: We perform a model-independent reconstruction of the cosmic expansion rate based on Type Ia supernova data. Using the Union2.1 data set, we show that the Hubble parameter behaviour allowed by the data without making any hypothesis about cosmological model or underlying gravity theory is consistent with a flat Λ cold dark matter universe having H0 = 70.43 ± 0.33 and Ωm = 0.297 ± 0.020, weakly dependent on the choice of initial scatter matrix. This is in closer agreement with the recently released Planck results (H0 = 67.3 ± 1.2, Ωm = 0.314 ± 0.020) than other standard analyses based on Type Ia supernova data. We argue this might be an indication that, in order to tackle subtle deviations from the standard cosmological model present in Type Ia supernova data, it is mandatory to go beyond parametrized approaches.
    Monthly Notices of the Royal Astronomical Society 11/2013; 436:854-858. · 5.52 Impact Factor
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    ABSTRACT: We use an unprecedented data-set of about 600 redshifts for cluster members, obtained as part of a VLT/VIMOS large programme, to constrain the mass profile of the z=0.44 cluster MACS J1206.2-0847 over the radial range 0-5 Mpc (0-2.5 virial radii) using the MAMPOSSt and Caustic methods. We then add external constraints from our previous gravitational lensing analysis. We invert the Jeans equation to obtain the velocity-anisotropy profiles of cluster members. With the mass-density and velocity-anisotropy profiles we then obtain the first determination of a cluster pseudo-phase-space density profile. The kinematics and lensing determinations of the cluster mass profile are in excellent agreement. This is very well fitted by a NFW model with mass M200=(1.4 +- 0.2) 10^15 Msun and concentration c200=6 +- 1, only slightly higher than theoretical expectations. Other mass profile models also provide acceptable fits to our data, of (slightly) lower (Burkert, Hernquist, and Softened Isothermal Sphere) or comparable (Einasto) quality than NFW. The velocity anisotropy profiles of the passive and star-forming cluster members are similar, close to isotropic near the center and increasingly radial outside. Passive cluster members follow extremely well the theoretical expectations for the pseudo-phase-space density profile and the relation between the slope of the mass-density profile and the velocity anisotropy. Star-forming cluster members show marginal deviations from theoretical expectations. This is the most accurate determination of a cluster mass profile out to a radius of 5 Mpc, and the only determination of the velocity-anisotropy and pseudo-phase-space density profiles of both passive and star-forming galaxies for an individual cluster [abridged]
    Astronomy and Astrophysics 10/2013; 558(A1). · 5.08 Impact Factor
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    ABSTRACT: We present VIsible Multi-Object Spectrograph (VIMOS) observations of a z 6 galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431 (z=0.348). This sub-L^*, high-z galaxy has been recently discovered by Monna et al. (2013) using dropout techniques with the 16-band HST photometry acquired as part of the Cluster Lensing And Supernova survey with Hubble (CLASH). Obtained as part of the CLASH-VLT survey, the VIMOS medium-resolution spectra of this source show a very faint continuum between ~8700A and ~9300A and a prominent emission line at 8643A, which can be readily identified with Lyman-alpha at z=6.110. The emission line exhibits an asymmetric profile, with a more pronounced red wing. The rest-frame equivalent width of the line is EW=79+-10A. After correcting for magnification, the star-formation rate (SFR) estimated from the Lya line is SFR(Lya)=11 M_{sol}/yr and that estimated from the UV data is SFR(UV)=3 M_{sol}/yr. We estimate that the effective radius of the source is R_e<~0.4 kpc, which implies a star formation surface mass density Sigma_{SFR}>6 M_{sol}/yr/kpc^2 and, using the Kennicutt-Schmidt relation, a gas surface mass density Sigma_{gas}>10^3 M_{sol}/pc^2. Our results support the idea that this magnified, distant galaxy is a young and compact object with 0.4 L^* at z=6, with comparable amount of mass in gas and stars. Future follow-up observations with ALMA will provide valuable insight into the SFR and molecular gas content of this source. In the spirit of the Frontier Fields initiative, we also publish the redshifts of several multiply imaged sources and other background objects which will help improving the strong lensing model of this galaxy cluster.
    09/2013;
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    ABSTRACT: We present a quintuply lensed z ~ 6 candidate discovered in the field of the galaxy cluster RXC J2248.7-4431 (z ~ 0.348) targeted within the Cluster Lensing and Supernova survey with Hubble (CLASH) and selected in the deep HST Frontier Fields survey. Thanks to the CLASH 16-band HST imaging, we identify the quintuply lensed z ~ 6 candidate as an optical dropout in the inner region of the cluster, the brightest image having magAB=24.81+-0.02 in the f105w filter. We perform a detailed photometric analysis to verify its hiz and lensed nature. We get as photometric redshift z_phot ~ 5.9, and given the extended nature and NIR colours of the lensed images, we rule out low-z early type and galactic star contaminants. We perform a strong lensing analysis of the cluster, using 11 families of multiple lensed images identified in the HST images. Our final best model predicts the hiz quintuply lensed system with a position accuracy of 0.8''. The magnifications of the five images are between 2.4 and 10, which leads to a delensed UV luminosity of L_1600 ~ 0.4L*_1600 at z=6. We also estimate the UV slope from the observed NIR colours, finding a steep beta=-2.89+-0.25. We use singular and composite stellar population SEDs to fit the photometry of the hiz candidate, and we conclude that it is a young (age <300 Myr) galaxy with mass of M ~ 10^8Msol, subsolar metallicity (Z<0.2Zsol) and low dust content (AV ~ 0.2-0.4).
    08/2013;
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    ABSTRACT: We utilize 16-band Hubble Space Telescope (HST) observations of 18 lensing clusters obtained as part of the Cluster Lensing And Supernova survey with Hubble (CLASH) Multi-Cycle Treasury program to search for z~6-8 galaxies. We report the discovery of 206, 45, and 13 Lyman-break galaxy (LBG) candidates at z~6, z~7, and z~8, respectively, identified from purely photometric redshift selections. This large sample, representing nearly an order of magnitude increase in the number of magnified star-forming galaxies at z~6-8 presented to date, is unique in that we have observations in four WFC3/UVIS UV, seven ACS/WFC optical and all five WFC3/IR broad-band filters, which enable very accurate photometric redshift selections. We construct detailed lensing models for all 18 clusters (although some are preliminary) to estimate object magnifications and to identify two new multiply-lensed z >~ 6 candidates. The median magnifications for these 18 clusters are 4, 4, and 5 for the z~6, z~7, and z~8 samples, respectively, over an average area of 4.5 arcmin^2 per cluster. We compare our observed number counts with expectations based on convolving "blank" field UV luminosity functions through our cluster lens models and find agreement down to ~27 mag, where we begin to suffer significant incompleteness. In all three redshift bins we find a higher number density at brighter observed magnitudes than the field predictions, in excellent agreement with the lensed expectations and clearly demonstrating the enhanced efficiency of lensing clusters over field surveys. Once again, lensing clusters appear to be a powerful tool in the discovery and study of high-redshift galaxies and allow for the first glimpse of faint galaxies beyond the reach of the deepest HST legacy field surveys, a technique that will continue be exploited with the upcoming ultradeep Hubble Frontier Fields campaign.
    08/2013;
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    ABSTRACT: We provide a new observational test for a key prediction of the \Lambda CDM cosmological model: the contributions of mergers with different halo-to-main-cluster mass ratios to cluster-sized halo growth. We perform this test by dynamically analyzing seven galaxy clusters, spanning the redshift range $0.13 < z_c < 0.45$ and caustic mass range $0.4-1.5$ $10^{15} h_{0.73}^{-1}$ M$_{\odot}$, with an average of 293 spectroscopically-confirmed bound galaxies to each cluster. The large radial coverage (a few virial radii), which covers the whole infall region, with a high number of spectroscopically identified galaxies enables this new study. For each cluster, we identify bound galaxies. Out of these galaxies, we identify infalling and accreted halos and estimate their masses and their dynamical states. Using the estimated masses, we derive the contribution of different mass ratios to cluster-sized halo growth. For mass ratios between ~0.2 and ~0.7, we find a ~1 $\sigma$ agreement with \Lambda CDM expectations based on the Millennium simulations I and II. At low mass ratios, $\lesssim 0.2$, our derived contribution is underestimated since the detection efficiency decreases at low masses, $\sim 2 \times 10^{14}$ $h_{0.73}^{-1}$ M$_{\odot}$. At large mass ratios, $\gtrsim 0.7$, we do not detect halos probably because our sample, which was chosen to be quite X-ray relaxed, is biased against large mass ratios. Therefore, at large mass ratios, the derived contribution is also underestimated.
    08/2013;
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    ABSTRACT: The Cluster Lensing And Supernovae survey with Hubble (CLASH) is an Hubble Space Telescope (HST) Multi-Cycle Treasury program observing 25 massive galaxy clusters. CLASH observations are carried out in 16 bands from UV to NIR to derive accurate and reliable estimates of photometric redshifts. We present the CLASH photometric redshifts and study the photometric redshift accuracy of the arcs in more detail for the case of MACS1206.2-0847. We use the publicly available Le Phare and BPZ photometric redshift codes on 17 CLASH galaxy clusters. Using Le Phare code for objects with StoN>=10, we reach a precision of 3%(1+z) for the strong lensing arcs, which is reduced to 2.4%(1+z) after removing outliers. For galaxies in the cluster field the corresponding values are 4%(1+z) and 3%(1+z). Using mock galaxy catalogues, we show that 3%(1+z) precision is what one would expect from the CLASH photometry when taking into account extinction from dust, emission lines and the finite range of SEDs included in the photo-z template library. We study photo-z results for different aperture photometry and find that the SExtractor isophotal photometry works best. Le Phare and BPZ give similar photo-z results for the strong lensing arcs as well as galaxies of the cluster field. Results are improved when optimizing the photometric aperture shape showing an optimal aperture size around 1" radius giving results which are equivalent to isophotal photometry. Tailored photometry of the arcs improve the photo-z results.
    07/2013;
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    ABSTRACT: We study structure formation in non-minimally coupled dark energy models, where there is a coupling in the Lagrangian between a quintessence scalar field and gravity via the Ricci scalar. We consider models with a range of different non-minimal coupling strengths and compare these to minimally coupled quintessence models with time-dependent dark energy densities. The equations of state of the latter are tuned to either reproduce the equation of state of the non-minimally coupled models or their background history. Thereby they provide a reference to study the unique imprints of coupling on structure formation. We show that the coupling between gravity and the scalar field, which effectively results in a time-varying gravitational constant G, is not negligible and its effect can be distinguished from a minimally coupled model. We extend previous work on this subject by showing that major differences appear in the determination of the mass function at high masses, where we observe differences of the order of 40% at z=0. Our new results concern effects on the non-linear matter power spectrum and on the lensing signal (differences of ~10% for both quantities), where we find that non-minimally coupled models could be distinguished from minimally coupled ones.
    Monthly Notices of the Royal Astronomical Society 07/2013; 437(1). · 5.52 Impact Factor
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    ABSTRACT: Growing observational evidence now indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z~5-7 galaxies observed with Spitzer. This line emission makes z~5-7 galaxies appear more massive, with lower specific star formation rates. However, corrections for this line emission have been very difficult to perform reliably due to huge uncertainties on the overall strength of such emission at z>~5.5. Here, we present the most direct observational evidence yet for ubiquitous high-EW [OIII]+Hbeta line emission in Lyman-break galaxies at z~7, while also presenting a strategy for an improved measurement of the sSFR at z~7. We accomplish this through the selection of bright galaxies in the narrow redshift window z~6.6-7.0 where the IRAC 4.5 micron flux provides a clean measurement of the stellar continuum light. Observed 4.5 micron fluxes in this window contrast with the 3.6 micron fluxes which are contaminated by the prominent [OIII]+Hbeta lines. To ensure a high S/N for our IRAC flux measurements, we consider only the brightest (H_{160}<26 mag) magnified galaxies we have identified in CLASH and other programs targeting galaxy clusters. Remarkably, the mean rest-frame optical color for our bright seven-source sample is very blue, [3.6]-[4.5]=-0.9+/-0.3. Such blue colors cannot be explained by the stellar continuum light and require that the rest-frame EW of [OIII]+Hbeta be greater than 637 Angstroms for the average source. The bluest four sources from our seven-source sample require an even more extreme EW of 1582 Angstroms. Our derived lower limit for the mean [OIII]+Hbeta EW could underestimate the true EW by ~2x based on a simple modeling of the redshift distribution of our sources. We can also set a robust lower limit of >~4 Gyr^-1 on the specific star formation rates based on the mean SED for our seven-source sample. (abridged)
    07/2013;
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    ABSTRACT: In this work we analyze the mass distribution of MACSJ1206.2-0847, especially focusing on the halo properties of its cluster members. The cluster appears relaxed in its X-ray emission, but has significant amounts of intracluster light which is not centrally concentrated, suggesting that galaxy-scale interactions are still ongoing despite the overall relaxed state. The cluster lenses 12 background galaxies into multiple images and one galaxy at $z=1.033$ into a giant arc and its counterimage. The multiple image positions and the surface brightness distribution (SFB) of the arc which is bent around several cluster members are sensitive to the cluster galaxy halo properties. We model the cluster mass distribution with a NFW profile and the galaxy halos with two parameters for the mass normalization and extent of a reference halo assuming scalings with their observed NIR--light. We match the multiple image positions at an r.m.s. level of $0.85\arcsec$ and can reconstruct the SFB distribution of the arc in several filters to a remarkable accuracy based on this cluster model. The length scale where the enclosed galaxy halo mass is best constrained is about 5 effective radii -- a scale in between those accessible to dynamical and field strong lensing mass estimates on one hand and galaxy--galaxy weak lensing results on the other hand. The velocity dispersion and halo size of a galaxy with $m_{\rm 160W,AB}=19.2$ or $M_{\rm B,Vega}=-20.7$ are $\sigma=150 \rm kms^{-1}$ and $r\approx 26\pm 6 \rm kpc$, indicating that the halos of the cluster galaxies are tidally stripped. We also reconstruct the unlensed source (which is smaller by a factor of $\sim5.8$ in area), demonstrating the increase of morphological information due to lensing and conclude that this galaxy has likely star--forming spiral arms with a red (older) central component.
    The Astrophysical Journal 06/2013; 774(2). · 6.73 Impact Factor

Publication Stats

4k Citations
915.15 Total Impact Points

Institutions

  • 2004–2014
    • Universität Heidelberg
      • • Institute of Theoretical Physics
      • • Centre for Astronomy (ZAH)
      Heidelburg, Baden-Württemberg, Germany
  • 2011–2013
    • Space Telescope Science Institute
      Baltimore, Maryland, United States
  • 2012
    • Universidad del País Vasco / Euskal Herriko Unibertsitatea
      • Theoretical physics and Science History
      Leioa, Basque Country, Spain
    • University College London
      • Department of Physics and Astronomy
      Londinium, England, United Kingdom
    • Leiden University
      • Leiden Observartory
      Leiden, South Holland, Netherlands
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
    • University of California, San Diego
      • Center for Astrophysics and Space Sciences (CASS)
      San Diego, California, United States
  • 2009
    • Heidelberger Institut für Theoretische Studien
      Heidelburg, Baden-Württemberg, Germany
  • 1993–2009
    • Max Planck Institute for Astrophysics
      Arching, Bavaria, Germany
  • 2008
    • Northeast Institute of Geography and Agroecology
      • Shanghai Astronomical Observatory
      Peping, Beijing, China
  • 2004–2005
    • University of Bologna
      • Department of Physics and Astronomy DIFA
      Bologna, Emilia-Romagna, Italy
  • 2002
    • University of Chicago
      • Department of Astronomy and Astrophysics
      Chicago, Illinois, United States
  • 2000
    • University of Padova
      Padua, Veneto, Italy