italo balestra | Ludwig-Maximilians-Universität München (original) (raw)

Papers by italo balestra

Recent work based on a global measurement of the ICM properties find evidence for an increase of ... more Recent work based on a global measurement of the ICM properties find evidence for an increase of the iron abundance in galaxy clusters with temperature around 2-4 keV. We have undertaken a study of the metal distribution in nearby clusters in this temperature range, aiming at resolving spatially the metal content of the ICM. The XMM observation of the first

Astronomy & Astrophysics, 2015

The Astrophysical Journal, 2015

We present high resolution (9 ) imaging of the Sunyaev-Zel'dovich Effect (SZE) toward two massive... more We present high resolution (9 ) imaging of the Sunyaev-Zel'dovich Effect (SZE) toward two massive galaxy clusters, MACS J0647.7+7015 (z = 0.591) and MACS J1206.2-0847 (z = 0.439). We compare these 90 GHz measurements, taken with the MUSTANG receiver on the Green Bank Telescope, with generalized Navarro-Frenk-White (gNFW) models derived from Bolocam 140 GHz SZE data as well as maps of the thermal gas derived from Chandra X-ray observations. For MACS J0647.7+7015, we find a gNFW profile with core slope parameter γ = 0.9 fits the MUSTANG image with χ 2 red = 1.005 and probability to exceed (PTE) = 0.34. For MACS J1206.2-0847, we find γ = 0.7, χ 2 red = 0.993, and PTE = 0.70. In addition, we find a significant (>3-σ) residual SZE feature in MACS J1206.2-0847 coincident with a group of galaxies identified in VLT data and filamentary structure found in a weak-lensing mass reconstruction. We suggest the detected sub-structure may be the SZE decrement from a low mass foreground group or an infalling group. GMRT measurements at 610 MHz reveal diffuse extended radio emission to the west, which we posit is either an AGN-driven radio lobe, a bubble expanding away from disturbed gas associated with the SZE signal, or a bubble detached and perhaps re-accelerated by sloshing within the cluster. Using the spectroscopic redshifts available, we find evidence for a foreground (z = 0.423) or infalling group, coincident with the residual SZE feature.

Astronomy & Astrophysics, 2015

Aims. In the effort to understand the link between the structure of galaxy clusters and their gal... more Aims. In the effort to understand the link between the structure of galaxy clusters and their galaxy populations, we focus on MACSJ1206.2-0847, at z ∼ 0.44, probing its substructure in the projected phase space through the spectrophotometric properties of a large number of galaxies from the CLASH-VLT survey. Methods. Our analysis is mainly based on an extensive spectroscopic dataset of 445 member galaxies, mostly acquired with VIMOS@VLT as part of our ESO Large Programme, sampling the cluster out to a radius ∼ 2R 200 (4 h −1 70 Mpc). We classify 412 galaxies as: passive, with strong Hδ absorption (red and blue ones), and with emission lines from weak to very strong ones. A number of tests for substructure detection is applied to analyze the galaxy distribution in the velocity space, in the 2D space, and in the (3D) projected phase-space. Results. Studied in its entirety, the cluster appears as a large-scale relaxed system with a few, secondary, minor overdensities in 2D distribution. We detect no velocity gradient or evidence of deviations in local mean velocities. The main feature is the WNW-ESE elongation. The analysis of galaxy populations per spectral class highlights a more complex scenario. The passive and red strong Hδ galaxies trace the cluster center and the WNW-ESE elongated structure. The red strong Hδ galaxies also mark a secondary, dense peak ∼ 2 h −1 70 Mpc at ESE. The emission line galaxies cluster in several loose structures, mostly outside R 200 . Two of these structures are also detected through our 3D analysis. The observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the direction of the main cluster accretion, traced by passive and red strong Hδ galaxies. The latter ones, interpreted as poststarburst galaxies, date a likely important event 1-2 Gyr before the epoch of observation. The emission line galaxies trace a secondary, ongoing infall where groups are accreted along several directions.

Proceedings of the International Astronomical Union, 2014

ABSTRACT We investigate the environmental dependence of the mass-metallicty (MZ) relation and it&... more ABSTRACT We investigate the environmental dependence of the mass-metallicty (MZ) relation and it's connection to galaxy stellar structures and morphologies. In our studies, we analyze galaxies in massive clusters at z~0.4 from the CLASH (HST) and CLASH-VLT surveys and measure their gas metallicities, star-formation rates, stellar structures and morphologies. We establish the MZ relation for 90 cluster and 40 field galaxies finding a shift of ~-0.3 dex in comparison to the local trends seen in SDSS for the majority of galaxies with logM<10.5. We do not find significant differences of the distribution of 4 distinct morphological types that we introduce by our classification scheme (smooth, disc-like, peculiar, compact). Some variations between cluster and field galaxies in the MZ relation are visible at the high mass end. However, obvious trends for cluster specific interactions (enhancements or quenching of SFRs) are missing. In particular, galaxies with peculiar stellar structures that hold signs for galaxy interactions, are distributed in a similar way as disc-like galaxies - in SFRs, masses and O/H abundances. We further show that our sample falls around an extrapolation of the star-forming main sequence (the SFR-M* relation) at this redshift, indicating that emission-line selected samples do not have preferentially high star-formation rates (SFRs). However, we find that half of the high mass cluster members (M*>10^10Msun) lie below the main sequence which corresponds to the higher mass objects that reach solar abundances in the MZ diagram.

The Astrophysical Journal, 2014

We utilize 16-band Hubble Space Telescope (HST ) observations of 18 lensing clusters obtained as ... more 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.

The Astrophysical Journal, 2015

We present a new determination of the concentration-mass relation for galaxy clusters based on ou... more 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 groundbased 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 × 10 15 M /h and 1.76 × 10 15 M /h and the halo concentrations are distributed around c 200c ∼ 3.7 with a 1σ 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.

The Astrophysical Journal, 2014

We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodyna... more We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodynamical 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 linesof-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 unrelaxed systems. For such a heterogeneous 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.

The Astrophysical Journal, 2015

We present a detailed mass reconstruction and a novel study on the substructure properties in the... more We present a detailed mass reconstruction and a novel study on the substructure properties in the core of the Cluster Lensing And Supernova survey with Hubble (CLASH) and Frontier Fields galaxy cluster MACS J0416.1−2403. We show and employ our extensive spectroscopic data set taken with the VIsible Multi-Object Spectrograph (VIMOS) instrument as part of our CLASH-VLT program, to confirm spectroscopically 10 strong lensing systems and to select a sample of 175 plausible cluster members to a limiting stellar mass of log(M * /M ⊙ ) ≃ 8.6. We reproduce the measured positions of a set of 30 multiple images with a remarkable median offset of only 0.3 ′′ by means of a comprehensive strong lensing model comprised of 2 cluster dark-matter halos, represented by cored elliptical pseudoisothermal mass distributions, and the cluster member components, parametrized with dual pseudoisothermal total mass profiles. The latter have total mass-to-light ratios increasing with the galaxy HST /WFC3 near-IR (F160W) luminosities. The measurement of the total enclosed mass within the Einstein radius is accurate to ∼ 5%, including systematic uncertainties. We emphasize that the use of multiple-image systems with spectroscopic redshifts and knowledge of cluster membership based on extensive spectroscopic information is key to constructing robust high-resolution mass maps. We also produce magnification maps over the central area that is covered with HST observations. We investigate the galaxy contribution, both in terms of total and stellar mass, to the total mass budget of the cluster. When compared with the outcomes of cosmological N -body simulations, our results point to a lack of massive subhalos in the inner regions of simulated clusters with total masses similar to that of MACS J0416.1−2403. Our findings of the location and shape of the cluster dark-matter halo density profiles and on the cluster substructures provide intriguing tests of the assumed collisionless, cold nature of dark matter and of the role played by baryons in the process of structure formation.

The Astrophysical Journal, 2014

ABSTRACT In the local universe, there is good evidence that, at a given stellar mass M, the gas-p... more ABSTRACT In the local universe, there is good evidence that, at a given stellar mass M, the gas-phase metallicity Z is anti-correlated with the star formation rate (SFR) of the galaxies. It has also been claimed that the resulting Z(M, SFR) relation is invariant with redshift—the so-called "fundamental metallicity relation" (FMR). Given a number of difficulties in determining metallicities, especially at higher redshifts, the form of the Z(M, SFR) relation and whether it is really independent of redshift is still very controversial. To explore this issue at z > 2, we used VLT-SINFONI and Subaru-MOIRCS near-infrared spectroscopy of 20 zCOSMOS-deep galaxies at 2.1 < z < 2.5 to measure the strengths of up to five emission lines: [O II] λ3727, Hβ, [O III] λ5007, Hα, and [N II] λ6584. This near-infrared spectroscopy enables us to derive O/H metallicities, and also SFRs from extinction corrected Hα measurements. We find that the mass-metallicity relation (MZR) of these star-forming galaxies at z 2.3 is lower than the local Sloan Digital Sky Survey (SDSS) MZR by a factor of three to five, a larger change than found by Erb et al. using [N II]/Hα-based metallicities from stacked spectra. We discuss how the different selections of the samples and metallicity calibrations used may be responsible for this discrepancy. The galaxies show direct evidence that the SFR is still a second parameter in the MZR at these redshifts. However, determining whether the Z(M, SFR) relation is invariant with epoch depends on the choice of extrapolation used from local samples, because z > 2 galaxies of a given mass have much higher SFRs than the local SDSS galaxies. We find that the zCOSMOS galaxies are consistent with a non-evolving FMR if we use the physically motivated formulation of the Z(M, SFR) relation from Lilly et al., but not if we use the empirical formulation of Mannucci et al.

The Astrophysical Journal, 2015

We present results from a comprehensive lensing analysis in Hubble Space Telescope (HST) data, of... more We present results from a comprehensive lensing analysis in Hubble Space Telescope (HST) data, of the complete Cluster Lensing And Supernova survey with Hubble (CLASH) cluster sample. In most galaxy clusters we identify new multiple-images previously undiscovered, allowing improved or, in some cases, first constraints on the cluster inner mass distributions and profiles. We combine these strong-lensing constraints with weak lensing shape measurements within the HST field-of-view (FOV), to jointly constrain the mass distributions. In nearly all clusters the analysis is performed in two different common parameterizations (one adopts light-traces-mass for both galaxies and dark matter while the other adopts an analytical, elliptical NFW form for the dark matter), to provide a better assessment of the underlying systematics. The characterization of systematics between different lens modeling techniques is most important in the current era of precision cosmology and deep cluster and lensing surveys such as CLASH and the Hubble Frontier Fields, especially when studying high-redshift magnified objects. We find that the typical (median), relative systematic differences throughout the central [4.6 × 4.6 ] analysis FOV, are ∼ 40% in the (dimensionless) mass density, κ, and ∼ 20% in the magnification, µ. We show maps of these differences for each cluster, as well as the mass distributions, critical curves, and 2D integrated mass profiles. For the Einstein radii (z s = 2) we find that all typically agree within 10% between the two models, and Einstein masses agree, typically, within ∼ 15%. At larger radii, the total projected, 2D integrated mass profiles of the two models, within r ∼ 2 , differ by ∼ 30%. Stacking the surface-density profiles of the sample from the two methods together, we obtain an average slope of d log(Σ)/d log(r) ∼ −0.64 ± 0.1, in the radial range [5,350] kpc. Lastly, we examine the behavior of the average magnification, surface density, and shear differences between the two models, as a function of both the radius (normalized to the Einstein radius of each cluster) and the best-fit values of these quantities, uncovering some interesting trends. All mass models and magnification maps are made publicly available for the community.

ABSTRACT The GOODS/VIMOS spectroscopic campaign is structured in two separate surveys using two d... more ABSTRACT The GOODS/VIMOS spectroscopic campaign is structured in two separate surveys using two different VIMOS grisms. The VIMOS Low Resolution Blue (LR-Blue) and Medium Resolution (MR) orange grisms have been used to cover different redshift ranges. The LR-Blue campaign is aimed at observing galaxies mainly at 1.8

We present a compared analysis of a 23 ks XMM-Newton and a 47 ks Chandra observation of the Ultra... more We present a compared analysis of a 23 ks XMM-Newton and a 47 ks Chandra observation of the Ultraluminous Infrared Galaxy Mrk 273. The hard X-ray spectrum can be modelled by a highly absorbed (∼ 7 × 10 23 cm −2 ) power law plus a Fe Kα emission line. The Fe line is broad (σ = 260 +370 −170 eV), suggesting possible superposition of a neutral line at 6.4 keV and a blend of ionized iron lines from Fe XXV and XXVI. The broad band spectrum requires three collisionally ionized plasma components, which may be associated with star-forming regions, having temperatures of about 0.3, 0.8 and 5 keV. The thermal emission at ∼ 0.3 keV extends on ∼ 45 kpc embracing the long tidal tail of the merger. Interestingly, thermal emission at ∼ 0.7 keV seems to be ubiquitous in ULIRGs, probably associated with circumnuclear starburst. A high temperature (kT > 5 keV) thermal component is also detected in two other ULIRGs (namely NGC 6240 and Arp 220). The absorption corrected Xray luminosity (L 2−10 keV ∼ 7×10 42 erg s −1 ) is ∼ 0.2% of the far-IR luminosity, similar to typical values found in pure starbursts. The thermal contribution to the soft Xray luminosity is approximately 0.2 − 0.7 × 10 42 erg s −1 , comparable to those found in NGC 6240 and other starburst dominated ULIRGs.

ABSTRACT The primary observing mode of the VLT visible imager and multi-object/integral field spe... more ABSTRACT The primary observing mode of the VLT visible imager and multi-object/integral field spectrometer, VIMOS, is multi-object spectroscopy, for which pre-imaging with VIMOS is currently mandatory. We report on the results of a study of the astrometric calibration of the VIMOS imaging mode and the efforts to improve it. Based on this study, we announce the introduction of an option that allows users to omit the VIMOS pre-imaging step and create masks directly from sufficiently accurate astrometric catalogues.

ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the p... more ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the properties of dark matter. One of these key tests is the mass density profile of clusters - the concentration-mass relation. There is a reported tension between the observed concentration-mass relation and the one theoretically expected using simulated galaxy clusters, where the observed clusters appear to have higher concentration than simulated clusters of similar total mass. In The Cluster Lensing And Supernova survey with Hubble (CLASH), we use different and independent techniques to estimate the mass distribution in clusters. The comparison between different techniques offers an observational test of the techniques and understanding of the systematics. In this work, we estimate the concentration-mass relation for about 8 (at the 0.2< z &;lt; 0.6 redshift range) of the 20 X-ray selected CLASH clusters using galaxy dynamics. We use a unique spectroscopic data set with more than about 300 cluster members per cluster. Finally, we compare our results to the theoretical expected ones and to the estimations derived using the lensing technique.

ABSTRACT We report the LBT/MODS1 spectroscopic confirmation of two images of faint Lyman alpha em... more ABSTRACT We report the LBT/MODS1 spectroscopic confirmation of two images of faint Lyman alpha emitters at z=6.4 behind the Frontier Fields galaxy cluster MACSJ0717.5+3745. A wide range of lens models suggests that the two images are highly magnified, with a strong lower limit of mu>5. These are the faintest z>6 candidates spectroscopically confirmed to date. These may be also multiple images of the same z=6.4 source as supported by their similar intrinsic properties, but the lens models are inconclusive regarding this interpretation. To be cautious, we derive the physical properties of each image individually. Thanks to the high magnification, the observed near-infrared (restframe ultraviolet) part of the spectral energy distributions and Lya lines are well detected with S/N(m_1500)>~10 and S/N(Lya)~10-15. Adopting mu > 5, the absolute magnitudes, M_1500, and Lya fluxes, are fainter than -18.7 and 2.8x10^-18 erg/s/cm2, respectively. We find a very steep ultraviolet spectral slope beta=-3.0+/-0.5 (F_lambda=lambda^beta), implying that these are very young, dust-free and low metallicity objects, made of standard stellar populations or even extremely metal poor stars (age <~ 30 Myr, E(B-V)=0 and metallicity 0.0 - 0.2 Z/Z_solar). The objects are compact (< 1 kpc^2), and with a stellar mass M* < 10^8 M_solar. The presence of the Lya line and the intrinsic FWHM (<300 km/s) of these newborn objects do not exclude a possible leakage of ionizing radiation. We discuss the possibility that such faint galaxies may resemble those responsible for cosmic reionization.

Recent work based on a global measurement of the ICM properties find evidence for an increase of ... more Recent work based on a global measurement of the ICM properties find evidence for an increase of the iron abundance in galaxy clusters with temperature around 2-4 keV. We have undertaken a study of the metal distribution in nearby clusters in this temperature range, aiming at resolving spatially the metal content of the ICM. The XMM observation of the first

Astronomy & Astrophysics, 2015

The Astrophysical Journal, 2015

We present high resolution (9 ) imaging of the Sunyaev-Zel'dovich Effect (SZE) toward two massive... more We present high resolution (9 ) imaging of the Sunyaev-Zel'dovich Effect (SZE) toward two massive galaxy clusters, MACS J0647.7+7015 (z = 0.591) and MACS J1206.2-0847 (z = 0.439). We compare these 90 GHz measurements, taken with the MUSTANG receiver on the Green Bank Telescope, with generalized Navarro-Frenk-White (gNFW) models derived from Bolocam 140 GHz SZE data as well as maps of the thermal gas derived from Chandra X-ray observations. For MACS J0647.7+7015, we find a gNFW profile with core slope parameter γ = 0.9 fits the MUSTANG image with χ 2 red = 1.005 and probability to exceed (PTE) = 0.34. For MACS J1206.2-0847, we find γ = 0.7, χ 2 red = 0.993, and PTE = 0.70. In addition, we find a significant (>3-σ) residual SZE feature in MACS J1206.2-0847 coincident with a group of galaxies identified in VLT data and filamentary structure found in a weak-lensing mass reconstruction. We suggest the detected sub-structure may be the SZE decrement from a low mass foreground group or an infalling group. GMRT measurements at 610 MHz reveal diffuse extended radio emission to the west, which we posit is either an AGN-driven radio lobe, a bubble expanding away from disturbed gas associated with the SZE signal, or a bubble detached and perhaps re-accelerated by sloshing within the cluster. Using the spectroscopic redshifts available, we find evidence for a foreground (z = 0.423) or infalling group, coincident with the residual SZE feature.

Astronomy & Astrophysics, 2015

Aims. In the effort to understand the link between the structure of galaxy clusters and their gal... more Aims. In the effort to understand the link between the structure of galaxy clusters and their galaxy populations, we focus on MACSJ1206.2-0847, at z ∼ 0.44, probing its substructure in the projected phase space through the spectrophotometric properties of a large number of galaxies from the CLASH-VLT survey. Methods. Our analysis is mainly based on an extensive spectroscopic dataset of 445 member galaxies, mostly acquired with VIMOS@VLT as part of our ESO Large Programme, sampling the cluster out to a radius ∼ 2R 200 (4 h −1 70 Mpc). We classify 412 galaxies as: passive, with strong Hδ absorption (red and blue ones), and with emission lines from weak to very strong ones. A number of tests for substructure detection is applied to analyze the galaxy distribution in the velocity space, in the 2D space, and in the (3D) projected phase-space. Results. Studied in its entirety, the cluster appears as a large-scale relaxed system with a few, secondary, minor overdensities in 2D distribution. We detect no velocity gradient or evidence of deviations in local mean velocities. The main feature is the WNW-ESE elongation. The analysis of galaxy populations per spectral class highlights a more complex scenario. The passive and red strong Hδ galaxies trace the cluster center and the WNW-ESE elongated structure. The red strong Hδ galaxies also mark a secondary, dense peak ∼ 2 h −1 70 Mpc at ESE. The emission line galaxies cluster in several loose structures, mostly outside R 200 . Two of these structures are also detected through our 3D analysis. The observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the direction of the main cluster accretion, traced by passive and red strong Hδ galaxies. The latter ones, interpreted as poststarburst galaxies, date a likely important event 1-2 Gyr before the epoch of observation. The emission line galaxies trace a secondary, ongoing infall where groups are accreted along several directions.

Proceedings of the International Astronomical Union, 2014

ABSTRACT We investigate the environmental dependence of the mass-metallicty (MZ) relation and it&... more ABSTRACT We investigate the environmental dependence of the mass-metallicty (MZ) relation and it's connection to galaxy stellar structures and morphologies. In our studies, we analyze galaxies in massive clusters at z~0.4 from the CLASH (HST) and CLASH-VLT surveys and measure their gas metallicities, star-formation rates, stellar structures and morphologies. We establish the MZ relation for 90 cluster and 40 field galaxies finding a shift of ~-0.3 dex in comparison to the local trends seen in SDSS for the majority of galaxies with logM<10.5. We do not find significant differences of the distribution of 4 distinct morphological types that we introduce by our classification scheme (smooth, disc-like, peculiar, compact). Some variations between cluster and field galaxies in the MZ relation are visible at the high mass end. However, obvious trends for cluster specific interactions (enhancements or quenching of SFRs) are missing. In particular, galaxies with peculiar stellar structures that hold signs for galaxy interactions, are distributed in a similar way as disc-like galaxies - in SFRs, masses and O/H abundances. We further show that our sample falls around an extrapolation of the star-forming main sequence (the SFR-M* relation) at this redshift, indicating that emission-line selected samples do not have preferentially high star-formation rates (SFRs). However, we find that half of the high mass cluster members (M*>10^10Msun) lie below the main sequence which corresponds to the higher mass objects that reach solar abundances in the MZ diagram.

The Astrophysical Journal, 2014

We utilize 16-band Hubble Space Telescope (HST ) observations of 18 lensing clusters obtained as ... more 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.

The Astrophysical Journal, 2015

We present a new determination of the concentration-mass relation for galaxy clusters based on ou... more 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 groundbased 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 × 10 15 M /h and 1.76 × 10 15 M /h and the halo concentrations are distributed around c 200c ∼ 3.7 with a 1σ 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.

The Astrophysical Journal, 2014

We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodyna... more We present the results of a numerical study based on the analysis of the MUSIC-2 N-body/hydrodynamical 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 linesof-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 unrelaxed systems. For such a heterogeneous 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.

The Astrophysical Journal, 2015

We present a detailed mass reconstruction and a novel study on the substructure properties in the... more We present a detailed mass reconstruction and a novel study on the substructure properties in the core of the Cluster Lensing And Supernova survey with Hubble (CLASH) and Frontier Fields galaxy cluster MACS J0416.1−2403. We show and employ our extensive spectroscopic data set taken with the VIsible Multi-Object Spectrograph (VIMOS) instrument as part of our CLASH-VLT program, to confirm spectroscopically 10 strong lensing systems and to select a sample of 175 plausible cluster members to a limiting stellar mass of log(M * /M ⊙ ) ≃ 8.6. We reproduce the measured positions of a set of 30 multiple images with a remarkable median offset of only 0.3 ′′ by means of a comprehensive strong lensing model comprised of 2 cluster dark-matter halos, represented by cored elliptical pseudoisothermal mass distributions, and the cluster member components, parametrized with dual pseudoisothermal total mass profiles. The latter have total mass-to-light ratios increasing with the galaxy HST /WFC3 near-IR (F160W) luminosities. The measurement of the total enclosed mass within the Einstein radius is accurate to ∼ 5%, including systematic uncertainties. We emphasize that the use of multiple-image systems with spectroscopic redshifts and knowledge of cluster membership based on extensive spectroscopic information is key to constructing robust high-resolution mass maps. We also produce magnification maps over the central area that is covered with HST observations. We investigate the galaxy contribution, both in terms of total and stellar mass, to the total mass budget of the cluster. When compared with the outcomes of cosmological N -body simulations, our results point to a lack of massive subhalos in the inner regions of simulated clusters with total masses similar to that of MACS J0416.1−2403. Our findings of the location and shape of the cluster dark-matter halo density profiles and on the cluster substructures provide intriguing tests of the assumed collisionless, cold nature of dark matter and of the role played by baryons in the process of structure formation.

The Astrophysical Journal, 2014

ABSTRACT In the local universe, there is good evidence that, at a given stellar mass M, the gas-p... more ABSTRACT In the local universe, there is good evidence that, at a given stellar mass M, the gas-phase metallicity Z is anti-correlated with the star formation rate (SFR) of the galaxies. It has also been claimed that the resulting Z(M, SFR) relation is invariant with redshift—the so-called "fundamental metallicity relation" (FMR). Given a number of difficulties in determining metallicities, especially at higher redshifts, the form of the Z(M, SFR) relation and whether it is really independent of redshift is still very controversial. To explore this issue at z > 2, we used VLT-SINFONI and Subaru-MOIRCS near-infrared spectroscopy of 20 zCOSMOS-deep galaxies at 2.1 < z < 2.5 to measure the strengths of up to five emission lines: [O II] λ3727, Hβ, [O III] λ5007, Hα, and [N II] λ6584. This near-infrared spectroscopy enables us to derive O/H metallicities, and also SFRs from extinction corrected Hα measurements. We find that the mass-metallicity relation (MZR) of these star-forming galaxies at z 2.3 is lower than the local Sloan Digital Sky Survey (SDSS) MZR by a factor of three to five, a larger change than found by Erb et al. using [N II]/Hα-based metallicities from stacked spectra. We discuss how the different selections of the samples and metallicity calibrations used may be responsible for this discrepancy. The galaxies show direct evidence that the SFR is still a second parameter in the MZR at these redshifts. However, determining whether the Z(M, SFR) relation is invariant with epoch depends on the choice of extrapolation used from local samples, because z > 2 galaxies of a given mass have much higher SFRs than the local SDSS galaxies. We find that the zCOSMOS galaxies are consistent with a non-evolving FMR if we use the physically motivated formulation of the Z(M, SFR) relation from Lilly et al., but not if we use the empirical formulation of Mannucci et al.

The Astrophysical Journal, 2015

We present results from a comprehensive lensing analysis in Hubble Space Telescope (HST) data, of... more We present results from a comprehensive lensing analysis in Hubble Space Telescope (HST) data, of the complete Cluster Lensing And Supernova survey with Hubble (CLASH) cluster sample. In most galaxy clusters we identify new multiple-images previously undiscovered, allowing improved or, in some cases, first constraints on the cluster inner mass distributions and profiles. We combine these strong-lensing constraints with weak lensing shape measurements within the HST field-of-view (FOV), to jointly constrain the mass distributions. In nearly all clusters the analysis is performed in two different common parameterizations (one adopts light-traces-mass for both galaxies and dark matter while the other adopts an analytical, elliptical NFW form for the dark matter), to provide a better assessment of the underlying systematics. The characterization of systematics between different lens modeling techniques is most important in the current era of precision cosmology and deep cluster and lensing surveys such as CLASH and the Hubble Frontier Fields, especially when studying high-redshift magnified objects. We find that the typical (median), relative systematic differences throughout the central [4.6 × 4.6 ] analysis FOV, are ∼ 40% in the (dimensionless) mass density, κ, and ∼ 20% in the magnification, µ. We show maps of these differences for each cluster, as well as the mass distributions, critical curves, and 2D integrated mass profiles. For the Einstein radii (z s = 2) we find that all typically agree within 10% between the two models, and Einstein masses agree, typically, within ∼ 15%. At larger radii, the total projected, 2D integrated mass profiles of the two models, within r ∼ 2 , differ by ∼ 30%. Stacking the surface-density profiles of the sample from the two methods together, we obtain an average slope of d log(Σ)/d log(r) ∼ −0.64 ± 0.1, in the radial range [5,350] kpc. Lastly, we examine the behavior of the average magnification, surface density, and shear differences between the two models, as a function of both the radius (normalized to the Einstein radius of each cluster) and the best-fit values of these quantities, uncovering some interesting trends. All mass models and magnification maps are made publicly available for the community.

ABSTRACT The GOODS/VIMOS spectroscopic campaign is structured in two separate surveys using two d... more ABSTRACT The GOODS/VIMOS spectroscopic campaign is structured in two separate surveys using two different VIMOS grisms. The VIMOS Low Resolution Blue (LR-Blue) and Medium Resolution (MR) orange grisms have been used to cover different redshift ranges. The LR-Blue campaign is aimed at observing galaxies mainly at 1.8

We present a compared analysis of a 23 ks XMM-Newton and a 47 ks Chandra observation of the Ultra... more We present a compared analysis of a 23 ks XMM-Newton and a 47 ks Chandra observation of the Ultraluminous Infrared Galaxy Mrk 273. The hard X-ray spectrum can be modelled by a highly absorbed (∼ 7 × 10 23 cm −2 ) power law plus a Fe Kα emission line. The Fe line is broad (σ = 260 +370 −170 eV), suggesting possible superposition of a neutral line at 6.4 keV and a blend of ionized iron lines from Fe XXV and XXVI. The broad band spectrum requires three collisionally ionized plasma components, which may be associated with star-forming regions, having temperatures of about 0.3, 0.8 and 5 keV. The thermal emission at ∼ 0.3 keV extends on ∼ 45 kpc embracing the long tidal tail of the merger. Interestingly, thermal emission at ∼ 0.7 keV seems to be ubiquitous in ULIRGs, probably associated with circumnuclear starburst. A high temperature (kT > 5 keV) thermal component is also detected in two other ULIRGs (namely NGC 6240 and Arp 220). The absorption corrected Xray luminosity (L 2−10 keV ∼ 7×10 42 erg s −1 ) is ∼ 0.2% of the far-IR luminosity, similar to typical values found in pure starbursts. The thermal contribution to the soft Xray luminosity is approximately 0.2 − 0.7 × 10 42 erg s −1 , comparable to those found in NGC 6240 and other starburst dominated ULIRGs.

ABSTRACT The primary observing mode of the VLT visible imager and multi-object/integral field spe... more ABSTRACT The primary observing mode of the VLT visible imager and multi-object/integral field spectrometer, VIMOS, is multi-object spectroscopy, for which pre-imaging with VIMOS is currently mandatory. We report on the results of a study of the astrometric calibration of the VIMOS imaging mode and the efforts to improve it. Based on this study, we announce the introduction of an option that allows users to omit the VIMOS pre-imaging step and create masks directly from sufficiently accurate astrometric catalogues.

ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the p... more ABSTRACT Galaxy clusters play a key role in testing cosmological models and in constraining the properties of dark matter. One of these key tests is the mass density profile of clusters - the concentration-mass relation. There is a reported tension between the observed concentration-mass relation and the one theoretically expected using simulated galaxy clusters, where the observed clusters appear to have higher concentration than simulated clusters of similar total mass. In The Cluster Lensing And Supernova survey with Hubble (CLASH), we use different and independent techniques to estimate the mass distribution in clusters. The comparison between different techniques offers an observational test of the techniques and understanding of the systematics. In this work, we estimate the concentration-mass relation for about 8 (at the 0.2< z &;lt; 0.6 redshift range) of the 20 X-ray selected CLASH clusters using galaxy dynamics. We use a unique spectroscopic data set with more than about 300 cluster members per cluster. Finally, we compare our results to the theoretical expected ones and to the estimations derived using the lensing technique.

ABSTRACT We report the LBT/MODS1 spectroscopic confirmation of two images of faint Lyman alpha em... more ABSTRACT We report the LBT/MODS1 spectroscopic confirmation of two images of faint Lyman alpha emitters at z=6.4 behind the Frontier Fields galaxy cluster MACSJ0717.5+3745. A wide range of lens models suggests that the two images are highly magnified, with a strong lower limit of mu>5. These are the faintest z>6 candidates spectroscopically confirmed to date. These may be also multiple images of the same z=6.4 source as supported by their similar intrinsic properties, but the lens models are inconclusive regarding this interpretation. To be cautious, we derive the physical properties of each image individually. Thanks to the high magnification, the observed near-infrared (restframe ultraviolet) part of the spectral energy distributions and Lya lines are well detected with S/N(m_1500)>~10 and S/N(Lya)~10-15. Adopting mu > 5, the absolute magnitudes, M_1500, and Lya fluxes, are fainter than -18.7 and 2.8x10^-18 erg/s/cm2, respectively. We find a very steep ultraviolet spectral slope beta=-3.0+/-0.5 (F_lambda=lambda^beta), implying that these are very young, dust-free and low metallicity objects, made of standard stellar populations or even extremely metal poor stars (age <~ 30 Myr, E(B-V)=0 and metallicity 0.0 - 0.2 Z/Z_solar). The objects are compact (< 1 kpc^2), and with a stellar mass M* < 10^8 M_solar. The presence of the Lya line and the intrinsic FWHM (<300 km/s) of these newborn objects do not exclude a possible leakage of ionizing radiation. We discuss the possibility that such faint galaxies may resemble those responsible for cosmic reionization.