The IMACS Cluster Building Survey uses the wide field spectroscopic capabilities of the IMACS spectrograph on the 6.5 m Baade Telescope to survey the large-scale environment surrounding rich intermediate-redshift clusters of galaxies. The goal is to understand the processes which may be transforming star-forming field galaxies into quiescent cluster members as groups and individual galaxies fall into the cluster from the surrounding supercluster. This first paper describes the survey: the data taking and reduction methods. We provide new calibrations of star formation rates (SFRs) derived from optical and infrared spectroscopy and photometry. We demonstrate that there is a tight relation between the observed SFR per unit B luminosity, and the ratio of the extinctions of the stellar continuum and the optical emission lines. With this, we can obtain accurate extinction-corrected colors of galaxies. Using these colors as well as other spectral measures, we determine new criteria for the existence of ongoing and recent starbursts in galaxies.

We perform a strong lensing analysis of the merging galaxy cluster MACS J0416.1-2403 (M0416; z = 0.42) in recent CLASH/HST observations. We identify 70 new multiple images and candidates of 23 background sources in the range 0.7 less than or similar to z(phot) less than or similar to 6.14 including two probable high-redshift dropouts, revealing a highly elongated lens with axis ratio similar or equal to 5:1, and a major axis of similar to 100 '' (z(s) similar to 2). Compared to other well-studied clusters, M0416 shows an enhanced lensing efficiency. Although the critical area is not particularly large (similar or equal to 0.6 square'; z(s) similar to 2), the number of multiple images, per critical area, is anomalously high. We calculate that the observed elongation boosts the number of multiple images, per critical area, by a factor of similar to 2.5x, due to the increased ratio of the caustic area relative to the critical area. Additionally, we find that the observed separation between the two main mass components enlarges the critical area by a factor of similar to 2. These geometrical effects can account for the high number (density) of multiple images observed. We find in numerical simulations that only similar to 4% of the clusters (with M-vir >= 6 x 10(14) h(-1) M-circle dot) exhibit critical curves as elongated as in M0416.

Our searches in the CLASH data have found many high-redshift galaxy candidates. One object at z = 6.2 in MACS J0329-02 is quadruply lensed. Another object in MACS J1149+ 22 is at redshift z = 9.6 and AB=25.7, the first candidate at z > 9 that is bright enough for spectroscopic observations. The discovery of more than 80 galaxy candidates at z > 7 demonstrates the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The galaxy cluster MACS J0717.5+3745 (z = 0.55) is the largest known cosmic lens, with complex internal structures seen in deep X-ray, Sunyaev-Zel'dovich effect, and dynamical observations. We perform a combined weak-and strong-lensing analysis with wide-field BVR(c)i'z' Subaru/Suprime-Cam observations and 16-band Hubble Space Telescope observations taken as part of the Cluster Lensing And Supernova survey with Hubble. We find consistent weak distortion and magnification measurements of background galaxies and combine these signals to construct an optimally estimated radial mass profile of the cluster and its surrounding large-scale structure out to 5 Mpc h(-1). We find consistency between strong-lensing and weak-lensing in the region where these independent data overlap, <500 kpc h(-1). The two-dimensional weak-lensing map reveals a clear filamentary structure traced by distinct mass halos. We model the lensing shear field with nine halos, including the main cluster, corresponding to mass peaks detected above 2.5 sigma(kappa). The total mass of the cluster as determined by the different methods is M-vir approximate to (2.8 +/- 0.4) x 10(15) M-circle dot. Although this is the most massive cluster known at z > 0.5, in terms of extreme value statistics, we conclude that the mass of MACS J0717.5+3745 by itself is not in serious tension with Lambda CDM, representing only a similar to 2 sigma departure above the maximum simulated halo mass at this redshift.

In this work, we analyze the mass distribution of MACSJ1206.2-0847, particularly focusing on the halo properties of its cluster members. The cluster appears relaxed in its X-ray emission, but has a significant amount of intracluster light that 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 (SFB) distribution 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 Navarro-Frenk-White profile and the galaxy halos with two parameters for the mass normalization and the extent of a reference halo assuming scalings with their observed near-infrared light. We match the multiple image positions at an rms level of 0 ''.85 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 the one hand and galaxy-galaxy weak-lensing results on the other hand. The velocity dispersion and halo size of a galaxy with m(160W),(AB) = 19.2 and M-B,M-Vega = -20.7 are sigma = 150 km s(-1) and r approximate to 26 +/- 6 kpc, respectively, indicating that the halos of the cluster galaxies are tidally stripped. We also reconstruct the unlensed source, which is smaller by a factor of similar to 5.8 in area, demonstrating the increase in morphological information due to lensing. We conclude that this galaxy likely has star-forming spiral arms with a red (older) central component.

We present a quintuply lensed z similar to 6 candidate discovered in the field of the galaxy cluster RXC J2248.7-4431 (z similar to 0.348) targeted within the Cluster Lensing and Supernova survey with Hubble (CLASH) and selected in the deep Hubble Space Telescope (HST) frontier fields survey. Thanks to the CLASH 16-band HST imaging, we identify the quintuply lensed z similar to 6 candidate as an optical dropout in the inner region of the cluster, the brightest image having mag(AB) = 24.8 +/- 0.1 in the f105w filter. We perform a detailed photometric analysis to verify its high-z and lensed nature. We get as photometric redshift z(ph) similar to 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 13 families of multiple lensed images identified in the HST images. Our final best model predicts the high-z quintuply lensed system with a position accuracy of 0.8 arcsec. The magnifications of the five images are between 2.2 and 8.3, which leads to a delensed UV luminosity of L-1600 similar to 0.5L(1600)* at z=6. We also estimate the UV slope from the observed NIR colours, finding a steep beta = -2.89 +/- 0.38. We use singular and composite stellar population SEDs to fit the photometry of the high-z candidate, and we conclude that it is a young (age <300 Myr) galaxy with mass of M similar to 10(8) M-circle dot, subsolar metallicity (Z < 0.2 Z(circle dot)) and low dust content (A(V) similar to 0.2-0.4).

A pressureless scenario for the dark matter (DM) fluid is a widely adopted hypothesis, despite the absence of 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 << 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 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 Cluster Lensing And Supernova survey with Hubble. 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) + 2p(t))/(3 c(2) rho) = 0.00 +/- 0.15 (stat) +/- 0.08 (syst), averaged over the radial range 0.5Mpc <= r <= 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 Cluster Lensing And Supernova Survey with Hubble-Very Large Telescope program.

The slope of the star formation rate/stellar mass relation (the SFR "Main Sequence"; SFR-M-*) is not quite unity: specific star formation rates (SFR/M*) are weakly but significantly anti-correlated with M-*. Here we demonstrate that this trend may simply reflect the well-known increase in bulge mass-fractions-portions of a galaxy not forming stars-with M-*. Using a large set of bulge/disk decompositions and SFR estimates derived from the Sloan Digital Sky Survey, we show that re-normalizing SFR by disk stellar mass (sSFR(disk) SFR/M*, disk) reduces the M-* dependence of SF efficiency by similar to 0.25 dex per dex, erasing it entirely in some subsamples. Quantitatively, we find log sSFR(disk)-log M-* to have a slope beta(disk) is an element of [-0.20, 0.00] +/- 0.02 (depending on the SFR estimator and Main Sequence definition) for star-forming galaxies with M-* >= 10(10) M-circle dot and bulge mass-fractions B/T less than or similar to 0.6, generally consistent with a pure-disk control sample (beta(control) = -0.05 +/- 0.04). That ( SFR/M-*,M- disk ) is (largely) independent of host mass for star-forming disks has strong implications for aspects of galaxy evolution inferred from any SFR-M-* relation, including manifestations of "mass quenching" (bulge growth), factors shaping the star-forming stellar mass function (uniform d log M-*/dt for low-mass, disk-dominated galaxies), and diversity in star formation histories (dispersion in SFR(M-*, t)). Our results emphasize the need to treat galaxies as composite systems-not integrated masses-in observational and theoretical work.

Growing observational evidence indicates that nebular line emission has a significant impact on the rest-frame optical fluxes of z similar to 5-7 galaxies. This line emission makes z similar to 5-7 galaxies appear more massive, with lower specific star-formation rates (sSFRs). However, corrections for this line emission have been difficult to perform reliably because of huge uncertainties on the strength of such emission at z greater than or similar to 5.5. In this paper, we present the most direct observational evidence thus far for ubiquitous high-equivalent-width (EW) [O (III)]+ H beta line emission in Lyman-break galaxies at z similar to 7, and we present a strategy for an improved measurement of the sSFR at z similar to 7. We accomplish this through the selection of bright galaxies in the narrow redshift window z similar to 6.6-7.0 where the Spitzer/Infrared Array Camera (IRAC) 4.5 mu m flux provides a clean measurement of the stellar continuum light, in contrast with the 3.6 mu m flux, which is contaminated by the prominent [O III]+ H beta lines. To ensure a high signal-to-noise ratio for our IRAC flux measurements, we consider only the brightest (H-160 < 26 mag) magnified galaxies we have identified behind galaxy clusters. It is remarkable that 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 [O III]+ H beta is greater than 637 angstrom for the average source. The four bluest sources from our seven-source sample require an even more extreme EW of 1582 angstrom. We can also set a robust lower limit of greater than or similar to 4Gyr(-1) on the sSFR of our sample based on the mean spectral energy distribution.

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 A383 (z = 0.187), respectively. Each SN was detected in Hubble Space Telescope 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 the classification of SN CLA11Tib is inconclusive. Using multi-color light-curve fits to determine a standardized SN Ia luminosity distance, we infer that SN CLO12Car was similar to 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 similar to 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 (in magnitude units, 2.5 log(10) mu): 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.