Canada France Hawaii Telescope Legacy Research Articles

All Puffed Up: Exploring Ultra-diffuse Galaxy Origins Through Galaxy Interactions

We present new follow-up observations of two ultra-diffuse galaxies (UDGs) selected for their distorted morphologies and tidal features, suggestive of tidal influence. Using Hubble Space Telescope Advanced Camera for Surveys F555W and F814W imaging, we identify 8 ± 2 globular clusters in KUG 0203-Dw1 and 6 ± 2 in KDG 013, abundances typical for normal dwarf galaxies of similar stellar mass. Jansky Very Large Array data reveal a clear H i detection of KUG 0203-Dw1 with a gas mass estimate of logMHI/M⊙≲7.4 and evidence of active stripping by the host, while KDG 013 has no clear gas detection. The UDGs likely originated as normal dwarf galaxies that have been subjected to significant stripping and tidal heating, causing them to become more diffuse. These two UDGs complete a sample of five exhibiting tidal features in the full Canada–France–Hawaii Telescope Legacy Survey area (∼1502 deg). These tidally influenced UDGs exhibit diverse properties; one stands out as a potential result of a dwarf merger, while the remainder suggest tidal heating origins. We also cannot conclusively rule out that these galaxies became UDGs in the field before processing by the group environment, underscoring the need for broader searches of diffuse galaxies to better understand the impact of galaxy interactions.

The Preexplosion Environments and the Progenitor of SN 2023ixf from the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX)

Supernova (SN) 2023ixf was discovered on 2023 May 19. The host galaxy, M101, was observed by the Hobby–Eberly Telescope Dark Energy Experiment collaboration over the period 2020 April 30–2020 July 10, using the Visible Integral-field Replicable Unit Spectrograph (3470 ≲ λ ≲ 5540 Å) on the 10 m Hobby–Eberly Telescope. The fiber filling factor within ±30″ of SN 2023ixf is 80% with a spatial resolution of 1″. The r < 5.″5 surroundings are 100% covered. This allows us to analyze the spatially resolved preexplosion local environments of SN 2023ixf with nebular emission lines. The two-dimensional maps of the extinction and the star formation rate (SFR) surface density (ΣSFR) show weak increasing trends in the radial distributions within the r < 5.″5 regions, suggesting lower values of extinction and SFR in the vicinity of the progenitor of SN 2023ixf. The median extinction and that of the surface density of SFR within r < 3″ are E(B − V) = 0.06 ± 0.14, and There is no significant change in extinction before and after the explosion. The gas metallicity does not change significantly with the separation from SN 2023ixf. The metal-rich branch of the R 23 calculations indicates that the gas metallicity around SN 2023ixf is similar to the solar metallicity (∼Z ☉). The archival deep images from the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) show a clear detection of the progenitor of SN 2023ixf in the z band at 22.778 ± 0.063 mag, but nondetections in the remaining four bands of CFHTLS (u, g, r, i). The results suggest a massive progenitor of ≈22 M ☉.

The Infrared Medium-deep Survey. IX. Discovery of Two New z ∼ 6 Quasars and Space Density Down to M 1450 ∼ −23.5 mag

We present the result of the Infrared Medium-deep Survey (IMS) z ∼ 6 quasar survey, using the combination of the IMS near-infrared images and the Canada–France–Hawaii Telescope Legacy Survey optical images. The traditional color selection method results in 25 quasar candidates over 86 deg2. We introduce the corrected Akaike information criterion (AICc) with the high-redshift quasar and late-type star models to prioritize the candidates efficiently. Among the color-selected candidates, seven plausible candidates finally passed the AICc selection, of which three are known quasars at z ∼ 6. The follow-up spectroscopic observations for the remaining four candidates were carried out, and we confirmed that two out of four are z ∼ 6 quasars. With this complete sample, we revisited the quasar space density at z ∼ 6 down to M 1450 ∼ −23.5 mag. Our result supports the low quasar space density at the luminosity where the quasar’s ultraviolet ionizing emissivity peaks, favoring a minor contribution of quasars to the cosmic reionization.

The Role of Dust, UV Luminosity and Large-scale Environment on the Escape of Lyα Photons: A Case Study of a Protocluster Field at z = 3.1

Abstract We present a detailed characterization of the Lyα properties for 93 Lyα emitters (LAEs) at z ∼ 3.1 selected from the D1 field of the Canada–France–Hawaii Telescope Legacy Survey, including 24 members of a massive protocluster. The median-stacked Lyα image shows an extended Lyα halo (LAH) surrounding the galaxy with the exponential scale length 4.9 ± 0.7 kpc, which accounts for roughly half of the total line flux. Accounting for the LAH contribution, the total Lyα escape fraction, f esc, is 40% ± 26%. Combining the data set with existing measurements, we find a dependence of f esc on the galaxy’s UV slope (β) and UV luminosity (L UV). The simultaneous use of both parameters allows prediction of f esc within 0.18 dex, a substantial improvement over 0.23 dex when only β is used. The correlation between f esc and E(B − V) suggests that Lyα photons undergo interstellar dust attenuation in a similar manner to continuum photons. Yet, Lyα transmission is typically higher than that expected for continuum photons at a similar wavelength by a factor, which depends on UV luminosity, up to 2 in the samples we studied. These results hint at complex geometries and physical conditions of the interstellar medium, which affect the Lyα transmission or production. Alternatively, the dust law may change with luminosity leading to an over- or underestimation of f esc. Finally, we report that protocluster LAEs tend to be bluer and more UV luminous than their field cousins, resulting in systematically higher f esc values. We speculate that it may be due to the widespread formation of young low-mass galaxies in dense gas-rich environments.

An obscured AGN population hidden in the VIPERS galaxies: identification through spectral energy distribution decomposition

ABSTRACT The detection of X-ray emission constitutes a reliable and efficient tool for the selection of active galactic nuclei (AGNs), although it may be biased against the most heavily absorbed AGNs. Simple mid-infrared (IR) broad-band selection criteria identify a large number of luminous and absorbed AGNs, yet again host contamination could lead to non-uniform and incomplete samples. Spectral energy distribution (SED) decomposition is able to decouple the emission from the AGN versus that from star-forming regions, revealing weaker AGN components. We aim to identify the obscured AGN population in the VIMOS Public Extragalactic Redshift Survey in the Canada–France–Hawaii Telescope Legacy Survey W1 field through SED modelling. We construct SEDs for 6860 sources and identify 160 AGNs at a high confidence level using a Bayesian approach. Using optical spectroscopy, we confirm the nature of ∼85 per cent of the AGNs. Our AGN sample is highly complete (∼92 per cent) compared to mid-IR colour-selected AGNs, including a significant number of galaxy-dominated systems with lower luminosities. In addition to the lack of X-ray emission (80 per cent), the SED fitting results suggest that the majority of the sources are obscured. We use a number of diagnostic criteria in the optical, IR, and X-ray regimes to verify these results. Interestingly, only 35 per cent of the most luminous mid-IR-selected AGNs have X-ray counterparts suggesting strong absorption. Our work emphasizes the importance of using SED decomposition techniques to select a population of type II AGNs, which may remain undetected by either X-ray or IR colour surveys.

LATIS: The Lyα Tomography IMACS Survey

Abstract We introduce LATIS, the Lyα Tomography IMACS Survey, a spectroscopic survey at Magellan designed to map the z = 2.2–2.8 intergalactic medium (IGM) in three dimensions by observing the Lyα forest in the spectra of galaxies and QSOs. Within an area of 1.7 deg2, we will observe approximately half of ≳L* galaxies at z = 2.2–3.2 for typically 12 hr, providing a dense network of sightlines piercing the IGM with an average transverse separation of 2.5 h −1 comoving Mpc (1 physical Mpc). At these scales, the opacity of the IGM is expected to be closely related to the dark matter density, and LATIS will therefore map the density field in the z ∼ 2.5 universe at ∼Mpc resolution over the largest volume to date. Ultimately, LATIS will produce approximately 3800 spectra of z = 2.2–3.2 galaxies that probe the IGM within a volume of 4 × 106 h −3 Mpc3, large enough to contain a representative sample of structures from protoclusters to large voids. Observations are already complete over one-third of the survey area. In this paper, we describe the survey design and execution. We present the largest IGM tomographic maps at comparable resolution yet made. We show that the recovered matter overdensities are broadly consistent with cosmological expectations based on realistic mock surveys, that they correspond to galaxy overdensities, and that we can recover structures identified using other tracers. LATIS is conducted in Canada–France–Hawaii Telescope Legacy Survey fields, including COSMOS. Coupling the LATIS tomographic maps with the rich data sets collected in these fields will enable novel studies of environment-dependent galaxy evolution and the galaxy–IGM connection at cosmic noon.

Discovery of Protoclusters at z ∼ 3.7 and 4.9: Embedded in Primordial Superclusters

Abstract We have carried out follow-up spectroscopy on three overdense regions of g- and r-dropout galaxies in the Canada–France–Hawaii Telescope Legacy Survey Deep Fields, finding two new protoclusters at z = 4.898 and 3.721 and a possible protocluster at z = 3.834. The z = 3.721 protocluster overlaps with a previously identified protocluster at z = 3.675. The redshift separation between these two protoclusters is Δz = 0.05, which is slightly larger than the size of typical protoclusters. Therefore, if they are not the progenitors of a &gt;1015 M ☉ halo, they would grow into closely located independent halos like a supercluster. The other protocluster at z = 4.898 is also surrounded by smaller galaxy groups. These systems including protoclusters and neighboring groups are regarded as the early phase of superclusters. We quantify the spatial distribution of member galaxies of the protoclusters at z = 3.675 and 3.721 by fitting triaxial ellipsoids, finding a tentative difference: one has a pancake-like shape, while the other is filamentary. This could indicate that these two protoclusters are in different stages of formation. We investigate the relation between redshift and the velocity dispersion of protoclusters, including other protoclusters from the literature, in order to compare their dynamical states. Although there is no significant systematic trend in the velocity dispersions of protoclusters with redshift, the distribution is skewed to higher velocity dispersion over the redshift range of z = 2–6. This could be interpreted as two phases of cluster formation, one dominated by the steady accretion of galaxies and the other by the merging between group-size halos, perhaps depending on the surrounding large-scale environments.

Deep ugrizY imaging and DEEP2/3 spectroscopy: a photometric redshift testbed for LSST and public release of data from the DEEP3 Galaxy Redshift Survey

ABSTRACT We present catalogues of calibrated photometry and spectroscopic redshifts in the Extended Groth Strip, intended for studies of photometric redshifts (photo-z’s). The data includes ugriz photometry from Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) and Y-band photometry from the Subaru Suprime camera, as well as spectroscopic redshifts from the DEEP2, DEEP3, and 3D-HST surveys. These catalogues incorporate corrections to produce effectively matched-aperture photometry across all bands, based upon object size information available in the catalogue and Moffat profile point spread function fits. We test this catalogue with a simple machine learning-based photometric redshift algorithm based upon Random Forest regression, and find that the corrected aperture photometry leads to significant improvement in photo-z accuracy compared to the original SExtractor catalogues from CFHTLS and Subaru. The deep ugrizY photometry and spectroscopic redshifts are well suited for empirical tests of photometric redshift algorithms for LSST. The resulting catalogues are publicly available at http://d-scholarship.pitt.edu/36064/. We include a basic summary of the strategy of the DEEP3 Galaxy Redshift Survey to accompany the recent public release of DEEP3 data.

Multiband Optical and Near-Infrared Properties of Faint Submillimeter Galaxies with Serendipitous ALMA Detections

Abstract We present a catalog of 26 faint submillimeter galaxies (SMGs) in the XMM Large Scale Structure (XMM-LSS) field identified by cross-matching serendipitously detected sources in archival pre–Atacama Large Millimeter Array (ALMA) band 6 and 7 data with multiband near-infrared (NIR) and optical data from the Spitzer Extragalactic Representative Volume Survey, the VISTA Deep Extragalactic Survey, the Canada–France–Hawaii Telescope Legacy Large Survey, and the Hyper Suprime-Cam Subaru Strategic Program. Of the 26 SMGs in our sample, 15 are identified here for the first time. The majority of the sources in our sample (16/26) have faint submillimeter fluxes (0.1 mJy &lt; S 1mm &lt; 1 mJy). In addition to the 26 SMGs with multiband optical and NIR detections, there are 60 highly reliable (&gt;5σ) ALMA sources with no counterpart in any other band down to an Infrared Array Camera (IRAC) [4.5] AB magnitude of ≈23.7. To further characterize the 26 galaxies with both ALMA and optical/NIR counterparts, we provide 13-band forced photometry for the entire catalog using the Tractor and calculate photometric redshifts and rest-frame colors. The median redshift of our sample is . We find that our sample galaxies have bluer colors compared to bright SMGs, and the UVJ color plot indicates that their colors are consistent with main-sequence star-forming galaxies. Our results provide new insights into the nature of the faint population of SMGs and also highlight opportunities for galaxy evolution studies based on archival ALMA data.

The XXL Survey

Context. The luminosity function (LF) is a powerful statistical tool used to describe galaxies and learn about their evolution. In particular, the LFs of galaxies inside clusters allow us to better understand how galaxies evolve in these dense environments. Knowledge of the LFs of galaxies in clusters is also crucial for clusters studies in the optical and near-infrared (NIR) as they encode, along with their density profiles, most of their observational properties. However, no consensus has been reached yet about the evolution of the cluster galaxy LF with halo mass and redshift. Aims. The main goal of this study is to investigate the LF of a sample of 142 X-ray selected clusters, with spectroscopic redshift confirmation and a well defined selection function, spanning a wide redshift and mass range, and to test the LF dependence on cluster global properties, in a homogeneous and unbiased way. Methods. Our study is based on the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) photometric galaxy catalogue, associated with photometric redshifts. We constructed LFs inside a scaled radius using a selection in photometric redshift around the cluster spectroscopic redshift in order to reduce projection effects. The width of the photometric redshift selection was carefully determined to avoid biasing the LF and depended on both the cluster redshift and the galaxy magnitudes. The purity was then enhanced by applying a precise background subtraction. We constructed composite luminosity functions (CLFs) by stacking the individual LFs and studied their evolution with redshift and richness, analysing separately the brightest cluster galaxy (BCG) and non-BCG members. We fitted the dependences of the CLFs and BCG distributions parameters with redshift and richness conjointly in order to distinguish between these two effects. Results. We find that the usual photometric redshift selection methods can bias the LF estimate if the redshift and magnitude dependence of the photometric redshift quality is not taken into account. Our main findings concerning the evolution of the galaxy luminosity distribution with redshift and richness are that, in the inner region of clusters and in the redshift-mass range we probe (about 0 &lt; z &lt; 1 and 1013 M⊙ &lt; M500 &lt; 5 × 1014 M⊙), the bright part of the LF (BCG excluded) does not depend much on mass or redshift except for its amplitude, whereas the BCG luminosity increases both with redshift and richness.

Complete IRAC Mapping of the CFHTLS-DEEP, MUSYC, and NMBS-II Fields

The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5 μm with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada–France–Hawaii Telescope Legacy Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 deg2, with at least ∼2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5 μm. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25% best-seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described here publicly available via the Spitzer Science Center.

Evidence for Ultra-diffuse Galaxy “Formation” through Galaxy Interactions

Abstract We report the discovery of two ultra-diffuse galaxies (UDGs) that show clear evidence of an association with tidal material and an interaction with a larger galaxy halo, found during a search of the Wide portion of the Canada–France–Hawaii Telescope Legacy Survey. The two new UDGs, NGC 2708-Dw1 and NGC 5631-Dw1, are faint (M g = −13.7 and −11.8 mag), extended (r h = 2.60 and 2.15 kpc), and have low central surface brightness (μ(g, 0) = 24.9 and 27.3 mag arcsec−2), while the stellar stream associated with each has a surface brightness μ(g) ≳ 28.2 mag arcsec−2. These observations provide evidence that the origin of some UDGs may connect to galaxy interactions, either by transforming normal dwarf galaxies by expanding them, or because UDGs can collapse out of tidal material (i.e., they are tidal dwarf galaxies). Further work is needed to understand the fraction of the UDG population “formed” through galaxy interactions, and wide field searches for diffuse dwarf galaxies will provide further clues to the origin of these enigmatic stellar systems.

The CFHQSIR survey: a Y-band extension of the CFHTLS-Wide survey

Context. The Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) has been conducted over a 5-yr period at the CFHT with the MegaCam instrument, totaling 450 nights of observations. The Wide Synoptic Survey is one component of the CFHTLS, covering 155 square degrees in four patches of 23 to 65 square degrees through the whole MegaCam filter set (u*, g’, r’, i’, z’) down to i’AB = 24.5. Aims. With the motivation of searching for high-redshift quasars at redshifts above 6.5, we extend the multi-wavelength CFHTLS-Wide data in the Y -band down to magnitudes of ~22.5 for point sources (5σ). Methods. We observed the four CFHTLS-Wide fields (except one quarter of the W3 field) in the Y -band with the Wide-field InfraRed Camera (WIRCam) at the CFHT. Each field was visited twice, at least three weeks apart. Each visit consisted of two dithered exposures. The images are reduced with the Elixir software used for the CFHTLS and modified to account for the properties of near-InfraRed (IR) data. Two series of image stacks are subsequently produced: four-image stacks for each WIRCam pointing, and one-square-degree tiles matched to the format of the CFHTLS data release. Photometric calibration is performed on stars by fitting stellar spectra to their CFHTLS photometric data and extrapolating their Y -band magnitudes. Results. After corrections accounting for correlated noise, we measure a limiting magnitude of YAB ≃ 22.4 for point sources (5σ) in an aperture diameter of 0.′′93, over 130 square degrees. We produce a multi-wavelength catalogue combining the CFHTLS-Wide optical data with our CFHQSIR (Canada–France High-z quasar survey in the near-InfraRed) Y -band data. We derive the Y -band number counts and compare them to the Vista Deep Extragalactic Observations survey (VIDEO). We find that the addition of the CFHQSIR Y -band data to the CFHTLS optical data increases the accuracy of photometric redshifts and reduces the outlier rate from 13.8% to 8.8% in the redshift range 1.05 ≲ z ≲ 1.2.

Models of gravitational lens candidates from Space Warps CFHTLS

We report modelling follow-up of recently-discovered gravitational-lens candidates in the Canada France Hawaii Telescope Legacy Survey. Lens modelling was done by a small group of specially-interested volunteers from the SpaceWarps citizen-science community who originally found the candidate lenses. Models are categorised according to seven diagnostics indicating (a) the image morphology and how clear or indistinct it is, (b) whether the mass map and synthetic lensed image appear to be plausible, and (c) how the lens-model mass compares with the stellar mass and the abundance-matched halo mass. The lensing masses range from ~10^11 Msun to >10^13 Msun. Preliminary estimates of the stellar masses show a smaller spread in stellar mass (except for two lenses): a factor of a few below or above ~10^11 Msun. Therefore, we expect the stellar-to-total mass fraction to decline sharply as lensing mass increases. The most massive system with a convincing model is J1434+522 (SW05). The two low-mass outliers are J0206-095 (SW19) and J2217+015 (SW42); if these two are indeed lenses, they probe an interesting regime of very low star-formation efficiency. Some improvements to the modelling software (SpaghettiLens), and discussion of strategies regarding scaling to future surveys with more and frequent discoveries, are included.

Next Generation Virgo Cluster Survey. XXI. The Weak Lensing Masses of the CFHTLS and NGVS RedGOLD Galaxy Clusters and Calibration of the Optical Richness

Abstract We measured stacked weak lensing cluster masses for a sample of 1323 galaxy clusters detected by the RedGOLD algorithm in the Canada–France–Hawaii Telescope Legacy Survey W1 and the Next Generation Virgo Cluster Survey at , in the optical richness range . This is the most comprehensive lensing study of a complete and pure optical cluster catalog in this redshift range. We test different mass models, and our final model includes a basic halo model with a Navarro Frenk and White profile, as well as correction terms that take into account cluster miscentering, non-weak shear, the two-halo term, the contribution of the Brightest Cluster Galaxy, and an a posteriori correction for the intrinsic scatter in the mass–richness relation. With this model, we obtain a mass–richness relation of (statistical uncertainties). This result is consistent with other published lensing mass–richness relations. We give the coefficients of the scaling relations between the lensing mass and X-ray mass proxies, L X and T X, and compare them with previous results. When compared to X-ray masses and mass proxies, our results are in agreement with most previous results and simulations, and consistent with the expected deviations from self-similarity.

An Optically Faint Quasar Survey at z ∼ 5 in the CFHTLS Wide Field: Estimates of the Black Hole Masses and Eddington Ratios

Abstract We present the result of our spectroscopic follow-up observation for faint quasar candidates at z ∼ 5 in part of the Canada–France–Hawaii Telescope Legacy Survey wide field. We select nine photometric candidates and identify three z ∼ 5 faint quasars, one z ∼ 4 faint quasar, and a late-type star. Since two faint quasar spectra show the C iv emission line without suffering from a heavy atmospheric absorption, we estimate their black hole masses ( ) and Eddington ratios ( ). The inferred are 9.04 ± 0.14 and 8.53 ± 0.20, respectively. In addition, the inferred are −1.00 ± 0.15 and −0.42 ± 0.22, respectively. If we adopt that , the seed black hole masses ( ) of our z ∼ 5 faint quasars are expected to be in most cases. We also compare the observational results with a mass accretion model, where angular momentum is lost due to supernova explosions. Accordingly, of the z ∼ 5 faint quasars in our sample can be explained even if is . Since z ∼ 6 luminous qusars and our z ∼ 5 faint quasars are not on the same evolutionary track, z ∼ 6 luminous quasars and our z ∼ 5 quasars are not the same populations but different populations, due to the difference of a period of the mass supply from host galaxies. Furthermore, we confirm that one can explain of z ∼ 6 luminous quasars and our z ∼ 5 faint quasars even if their seed black holes are formed at z ∼ 7.

The Galaxy–Halo Connection in High-redshift Universe: Details and Evolution of Stellar-to-halo Mass Ratios of Lyman Break Galaxies on CFHTLS Deep Fields

Abstract We present the results of clustering analyses of Lyman break galaxies (LBGs) at , 4, and 5 using the final data release of the Canada–France–Hawaii Telescope Legacy Survey (CFHTLS). Deep- and wide-field images of the CFHTLS Deep Survey enable us to obtain sufficiently accurate two-point angular correlation functions to apply a halo occupation distribution analysis. The mean halo masses, calculated as , increase with the stellar-mass limit of LBGs. The threshold halo mass to have a central galaxy, follows the same increasing trend as the low-z results, whereas the threshold halo mass to have a satellite galaxy, M 1, shows higher values at than , over the entire stellar mass range. Satellite fractions of dropout galaxies, even at less massive halos, are found to drop sharply, from z = 2 down to less than 0.04, at . These results suggest that satellite galaxies form inefficiently within dark halos at , even for less massive satellites with . We compute stellar-to-halo mass ratios (SHMRs) assuming a main sequence of galaxies, which is found to provide SHMRs consistent with those derived from a spectral energy distribution fitting method. The observed SHMRs are in good agreement with model predictions based on the abundance-matching method, within confidence intervals. We derive observationally, for the first time, , which is the halo mass at a peak in the star-formation efficiency, at , and it shows a small increasing trend with cosmic time at . In addition, and its normalization are found to be almost unchanged during . Our study provides observational evidence that galaxy formation is ubiquitously most efficient near a halo mass of over cosmic time.

THE NEXT GENERATION VIRGO CLUSTER SURVEY. XX. RedGOLD BACKGROUND GALAXY CLUSTER DETECTIONS

ABSTRACT We build a background cluster candidate catalog from the Next Generation Virgo Cluster Survey (NGVS) using our detection algorithm RedGOLD. The NGVS covers 104 deg2 of the Virgo cluster in the -bandpasses to a depth of g ∼ 25.7 mag (5σ). Part of the survey was not covered or has shallow observations in the r band. We build two cluster catalogs: one using all bandpasses, for the fields with deep r-band observations (∼20 deg2), and the other using four bandpasses ( ) for the entire NGVS area. Based on our previous Canada–France–Hawaii Telescope Legacy Survey W1 studies, we estimate that both of our catalogs are ∼100% (∼70%) complete and ∼80% pure, at z ≤ 0.6 (z ≲ 1), for galaxy clusters with masses of M ≳ 1014 M ⊙. We show that when using four bandpasses, though the photometric redshift accuracy is lower, RedGOLD detects massive galaxy clusters up to z ∼ 1 with completeness and purity similar to the five-band case. This is achieved when taking into account the bias in the richness estimation, which is ∼40% lower at 0.5 ≤ z &lt; 0.6 and ∼20% higher at 0.6 &lt; z &lt; 0.8, with respect to the five-band case. RedGOLD recovers all the X-ray clusters in the area with mass M 500 &gt; 1.4 × 1014 M ⊙ and 0.08 &lt; z &lt; 0.5. Because of our different cluster richness limits and the NGVS depth, our catalogs reach lower masses than the published redMaPPer cluster catalog over the area, and we recover ∼90%–100% of its detections.

WEAK GRAVITATIONAL LENSING ANALYSIS OF A SAMPLE OF 50 MASSIVE GALAXY CLUSTERS

Weak gravitational lensing is an ecient technique for detecting galaxy clusters and probing their mass distribution. We present a weak gravitational lensing analysis of a large sample of galaxy clusters. We have built a nearly complete sample of 50 optically rich clusters, located in the redshift range 0:1 < z < 0:6 and observed in the Canada France Hawaii Telescope Legacy Survey (CFHT-LS). We used weak gravitational lensing to measure, for each galaxy cluster, the density radial prole, the total mass and the mass-to-light ratio (by comparing with the total luminosity of the member galaxies). This project is a preliminary step towards the next analysis of the weak lensing galaxy clusters in the surveys KiDS and VOICE, which are currently collecting data with the VLT Survey Telescope, in Chile.

THE POPULATION OF GALAXY–GALAXY STRONG LENSES IN FORTHCOMING OPTICAL IMAGING SURVEYS

Ongoing and future imaging surveys represent significant improvements in depth, area, and seeing compared to current data sets. These improvements offer the opportunity to discover up to three orders of magnitude more galaxy–galaxy strong lenses than are currently known. In this work we forecast the number of lenses that will be discoverable in forthcoming surveys and simulate their properties. We generate a population of statistically realistic strong lenses and simulate observations of this population for the Dark Energy Survey (DES), the Large Synoptic Survey Telescope (LSST), and Euclid surveys. We verify our model against the galaxy-scale lens search of the Canada–France–Hawaii Telescope Legacy Survey, predicting 250 discoverable lenses compared to 220 found by Gavazzi et al. The predicted Einstein radius distribution is also remarkably similar to that found by Sonnenfeld et al. For future surveys we find that, assuming Poisson limited lens galaxy subtraction, searches of the DES, LSST, and Euclid data sets should discover 2400, 120000, and 170000 galaxy–galaxy strong lenses, respectively. Finders using blue-minus-red () difference imaging for lens subtraction can discover 1300 and 62000 lenses in DES and LSST. The uncertainties on the model are dominated by the high-redshift source population, which typically gives fractional errors on the discoverable lens number at the level of tens of percent. We find that doubling the signal-to-noise ratio required for a lens to be detectable approximately halves the number of detectable lenses in each survey, indicating the importance of understanding the selection function and the sensitivity of future lens finders in interpreting strong lens statistics. We make our population forecasting and simulated observation codes publicly available so that the selection function of strong lens finders can easily be calibrated.