A. Fritz

The VIMOS Public Extragalactic Redshift Survey (VIPERS) - Galaxy clustering and redshift-space distortions at z ≃ 0.8 in the first data release

We present in this paper the general real- and redshift-space clustering properties of galaxies as measured in the first data release of the VIPERS survey. VIPERS is a large redshift survey designed to probe the distant Universe and its large-scale structure at 0.5 < z < 1.2. We describe in this analysis the global properties of the sample and discuss the survey completeness and associated corrections. This sample allows us to measure the galaxy clustering with an unprecedented accuracy at these redshifts. From the redshift-space distortions observed in the galaxy clustering pattern we provide a first measurement of the growth rate of structure at z = 0.8: f\sigma_8 = 0.47 +/- 0.08. This is completely consistent with the predictions of standard cosmological models based on Einstein gravity, although this measurement alone does not discriminate between different gravity models.

A PHOTOMETRIC REDSHIFT OF z ∼ 9.4 FOR GRB 090429B

Gamma-ray bursts (GRBs) serve as powerful probes of the early universe, with their luminous afterglows revealing the locations and physical properties of star-forming galaxies at the highest redshifts, and potentially locating first-generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal-to-noise spectroscopy, or photometry. Here we present a photometric redshift of z ~ 9.4 for the Swift detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming a Small Magellanic Cloud dust law (which has been found in a majority of GRB sight lines), the 90% likelihood range for the redshift is 9.06 7. The non-detection of the host galaxy to deep limits (Y(AB) ~ 28, which would correspond roughly to 0.001L* at z = 1) in our late-time optical and infrared observations with the Hubble Space Telescope strongly supports the extreme-redshift origin of GRB 090429B, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs and suggest that its progenitor is not greatly different from those of lower redshift bursts.

The galaxy–halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field

We present new constraints on the relationship between galaxies and their host dark matter haloes, measured from the location of the peak of the stellar-to-halo mass ratio (SHMR), up to the most massive galaxy clusters at redshift z ∼ 0.8 and over a volume of nearly 0.1 Gpc3. We use a unique combination of deep observations in the CFHTLenS/VIPERS field from the near-UV to the near-IR, supplemented by ∼60 000 secure spectroscopic redshifts, analysing galaxy clustering, galaxy–galaxy lensing and the stellar mass function. We interpret our measurements within the halo occupation distribution (HOD) framework, separating the contributions from central and satellite galaxies. We find that the SHMR for the central galaxies peaks at Mh,peak=1.9+0.2−0.1×1012M⊙ Mh,peak=1.9−0.1+0.2×1012M⊙ with an amplitude of 0.025, which decreases to ∼0.001 for massive haloes ( Mh>1014M⊙ Mh>1014M⊙ ). Compared to central galaxies only, the total SHMR (including satellites) is boosted by a factor of 10 in the high-mass regime (cluster-size haloes), a result consistent with cluster analyses from the literature based on fully independent methods. After properly accounting for differences in modelling, we have compared our results with a large number of results from the literature up to z = 1: we find good general agreement, independently of the method used, within the typical stellar-mass systematic errors at low to intermediate mass ( M⋆<1011M⊙ M⋆<1011M⊙ ) and the statistical errors above. We have also compared our SHMR results to semi-analytic simulations and found that the SHMR is tilted compared to our measurements in such a way that they over- (under-) predict star formation efficiency in central (satellite) galaxies.

The VIMOS Public Extragalactic Redshift Survey (VIPERS) - A precise measurement of the galaxy stellar mass function and the abundance of massive galaxies at redshifts 0.5 < z < 1.3

We measure the evolution of the galaxy stellar mass function from z = 1.3 to z = 0.5 using the first 53 608 redshifts of the ongoing VIMOS Public Extragalactic Survey (VIPERS). Thanks to its large volume and depth, VIPERS provides a detailed picture of the galaxy distribution at z ≃ 0.8, when the Universe was ≃7 Gyr old. We carefully estimate the uncertainties and systematic effects associated with the SED fitting procedure used to derive galaxy stellar masses. We estimate the galaxy stellar mass function at several epochs between z = 0.5 and 1.3, discussing the amount of cosmic variance affecting our estimate in detail. We find that Poisson noise and cosmic variance of the galaxy mass function in the VIPERS survey are comparable to the statistical uncertainties of large surveys in the local universe. VIPERS data allow us to determine with unprecedented accuracy the high-mass tail of the galaxy stellar mass function, which includes a significant number of galaxies that are too rare to detect with any of the past spectroscopic surveys. At the epochs sampled by VIPERS, massive galaxies had already assembled most of their stellar mass. We compare our results with both previous observations and theoretical models. We apply a photometric classification in the (U − V) rest-frame colour to compute the mass function of blue and red galaxies, finding evidence for the evolution of their contribution to the total number density budget: the transition mass above which red galaxies dominate is found to be about 1010.4 ℳ⊙ at z ≃ 0.55, and it evolves proportionally to (1 + z)3. We are able to separately trace the evolution of the number density of blue and red galaxies with masses above 1011.4 ℳ⊙, in a mass range barely studied in previous work. We find that for such high masses, red galaxies show a milder evolution with redshift, when compared to objects at lower masses. At the same time, we detect a population of similarly massive blue galaxies, which are no longer detectable below z = 0.7. These results show the improved statistical power of VIPERS data, and give initial promising indications of mass-dependent quenching of galaxies at z ≃ 1.

The VIMOS Public Extragalactic Redshift Survey (VIPERS) ⋆ Luminosity and stellar mass dependence of galaxy clustering at 0.5< z< 1.1

Aims. We investigate the dependence of galaxy clustering on luminosity and stellar mass in the redshift range 0.5 < z < 1.1, using the first ~ 55 000 redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS). Methods. We measured the redshift-space two-point correlation functions (2PCF), ξ(s) and ξ(rp,π) , and the projected correlation function, wp(rp), in samples covering different ranges of B-band absolute magnitudes and stellar masses. We considered both threshold and binned galaxy samples, with median B-band absolute magnitudes − 21.6 ≲ MB − 5log (h) ≲ − 19.5 and median stellar masses 9.8 ≲ log (M⋆ [h-2 M⊙]) ≲ 10.7. We assessed the real-space clustering in the data from the projected correlation function, which we model as a power law in the range 0.2 < rp [h-1 Mpc ] < 20. Finally, we estimated the galaxy bias as a function of luminosity, stellar mass, and redshift, assuming a flat Λ cold dark matter model to derive the dark matter 2PCF. Results. We provide the best-fit parameters of the power-law model assumed for the real-space 2PCF – the correlation length, r0, and the slope, γ – as well as the linear bias parameter, as a function of the B-band absolute magnitude, stellar mass, and redshift. We confirm and provide the tightest constraints on the dependence of clustering on luminosity at 0.5 < z < 1.1. We prove the complexity of comparing the clustering dependence on stellar mass from samples that are originally flux-limited and discuss the possible origin of the observed discrepancies. Overall, our measurements provide stronger constraints on galaxy formation models, which are now required to match, in addition to local observations, the clustering evolution measured by VIPERS galaxies between z = 0.5 and z = 1.1 for a broad range of luminosities and stellar masses.

The VIMOS Public Extragalactic Redshift Survey (VIPERS): - A quiescent formation of massive red-sequence galaxies over the past 9 Gyr

We explore the evolution of the Colour-Magnitude Relation (CMR) and Luminosity Function (LF) at 0.4 10^11 M_sun) and expeditious RS formation over a short period of ~1.5 Gyr starting before z=1. This is supported by the detection of ongoing SF in ETGs at 0.9<z<1.0, in contrast with the quiescent red stellar populations of ETGs at 0.5<z<0.6. There is an increase in the observed CMR scatter with redshift, two times larger than in galaxy clusters and at variance with theoretical models. We discuss possible physical mechanisms that support the observed evolution of the red galaxy population. Our findings point out that massive galaxies have experienced a sharp SF quenching at z~1 with only limited additional merging. In contrast, less-massive galaxies experience a mix of SF truncation and minor mergers which build-up the low- and intermediate-mass end of the CMR.

Intracluster light properties in the CLASH-VLT cluster MACS J1206.2-0847

Aims. We aim constrain the assembly history of clusters by studying the intracluster light (ICL) properties, estimating its contribution to the fraction of baryons in stars, f∗, and understanding possible systematics or bias using different ICL detection techniques.Methods. 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, which is part of the CLASH sample. Using deep multiband Subaru images, we extracted the surface brightness (SB) profile of the BCG+ICL and 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.Results. The most peculiar feature of the ICL in MACS1206 is its asymmetric radial distribution, with an excess in the SE direction and extending toward the second brightest cluster galaxy, which is a post starburst galaxy. This suggests an interaction between the BCG and this galaxy that dates back to τ ≤ 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 stronger 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.

CLASH: Photometric redshifts with 16 HST bands in galaxy cluster fields

Context. The Cluster Lensing And Supernovae survey with Hubble (CLASH) is a Hubble Space Telescope (HST) Multi-Cycle Treasury programme that observes 25 massive galaxy clusters, 20 of which were X-ray-selected to preferably choose dynamically relaxed clusters, and 5 additional “high magnification” clusters, which were selected based on their optical lensing properties. CLASH aims to study the dark matter distribution of the clusters and find magnified high-redshift galaxies behind them. CLASH observations were carried out in 16 bands from UV to NIR to derive accurate and reliable estimates of photometric redshifts. Aims. We present the CLASH photometric redshifts using 16 HST bands and study the photometric redshift accuracy including a detailed comparison between photometric and spectroscopic redshifts for the strong lensing arcs using the measurements from the cluster MACSJ1206.2-0847. Methods. We used the publicly available Le Phare and BPZ photometric redshift estimation codes on 17 CLASH galaxy clusters for which the full photo-z data processing had been completed at the time of this analysis, and derive an estimate of the CLASH photo-z accuracy. Results. Using Le Phare code for objects with a S/N ≥ 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 is expected using the baseline sky substraction algorithm when taking into account extinction from dust, emission lines, and the finite range of SEDs included in the photo-z template library. An improved method for estimating galaxy colours that yields more accurate photometric redshifts will be explored in a forthcoming paper. We study photo-z results for different aperture photometry techniques and find that the SExtractor isophotal photometry works best. We check the robustness of the arcs photo-z results by rederiving the input photometry in the case of MACS1206. We describe and release a photometric redshift catalogue of the MACS1206 cluster we study. Conclusions. Our photo-z codes give similar results for the strong lensing arcs, as well as for galaxies of the cluster field. Results are improved when optimizing the photometric aperture shape that shows an optimal aperture size around 1′′ radius, giving results that are equivalent to isophotal photometry. Tailored photometry of the arcs improves the photo-z results by showing more consistency between the different arcs of the same strong lensing system.

CLASH-VLT : spectroscopic confirmation of a z = 6.11 quintuply lensed galaxy in the Frontier Fields cluster RXC J2248.7-4431

We present VIsible Multi-Object Spectrograph (VIMOS) observations of a galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431 . This sub-, high- 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 8700 a and 9300 a and a prominent emission line at 8643 , which can be readily identified with Lyman- at . The emission line exhibits an asymmetric profile, with a more pronounced red wing. The rest-frame equivalent width of the line is , relatively well constrained thanks to the detection of the UV continuum, which is rarely achieved for a sub- galaxy at this redshift. After correcting formagnification, the star formation rate (SFR) estimated from the Ly line is SFRLyyr and that estimated from the UV data is SFRUVyr. We estimate that the effective radius of the source is kpc, which implies a star formation surface mass density yrkpc and, using the Kennicutt-Schmidt relation, a gas surface mass density pc. Our results support the idea that this magnified, distant galaxy is a young and compact object with luminosity at , when the Universe was just 1 Gyr old, with a similar amount of mass in gas and stars. 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. This work is based on data collected at ESO VLT (prog.ID 186.A-0798) and at NASA HST.

CLASH-VLT: The stellar mass function and stellar mass density profile of the z = 0.44 cluster of galaxies MACS J1206.2-0847

Context. The study of the galaxy stellar mass function (SMF) in relation to the galaxy environment and the stellar mass density profile, ρ⋆(r), is a powerful tool to constrain models of galaxy evolution.Aims. We determine the SMF of the z = 0.44 cluster of galaxies MACS J1206.2-0847 separately for passive and star-forming (SF) galaxies, in different regions of the cluster, from the center out to approximately 2 virial radii. We also determine ρ⋆(r) to compare it to the number density and total mass density profiles. Methods. We use the dataset from the CLASH-VLT survey. Stellar masses are obtained by spectral energy distribution fitting with the MAGPHYS technique on 5-band photometric data obtained at the Subaru telescope. We identify 1363 cluster members down to a stellar mass of 109.5 M⊙, selected on the basis of their spectroscopic (~1/3 of the total) and photometric redshifts. We correct our sample for incompleteness and contamination by non members. Cluster member environments are defined using either the clustercentric radius or the local galaxy number density. Results. The whole cluster SMF is well fitted by a double Schechter function, which is the sum of the two Schechter functions that provide good fits to the SMFs of, separately, the passive and SF cluster populations. The SMF of SF galaxies is significantly steeper than the SMF of passive galaxies at the faint end. The SMF of the SF cluster galaxies does not depend on the environment. The SMF of the passive cluster galaxies has a significantly smaller slope (in absolute value) in the innermost (≤ 0.50 Mpc, i.e., ~0.25 virial radii), and in the highest density cluster region than in more external, lower density regions. The number ratio of giant/subgiant galaxies is maximum in this innermost region and minimum in the adjacent region, but then gently increases again toward the cluster outskirts. This is also reflected in a decreasing radial trend of the average stellar mass per cluster galaxy. On the other hand, the stellar mass fraction, i.e., the ratio of stellar to total cluster mass, does not show any significant radial trend. Conclusions. Our results appear consistent with a scenario in which SF galaxies evolve into passive galaxies due to density-dependent environmental processes and eventually get destroyed very near the cluster center to become part of a diffuse intracluster medium. Dynamical friction, on the other hand, does not seem to play an important role. Future investigations of other clusters of the CLASH-VLT sample will allow us to confirm our interpretation.