I. Apples to apples A2A^2: realistic galaxy simulated catalogs and photometric redshift predictions for next-generation surveys

We present new mock catalogues for two of the largest stage-IV next-generation surveys in the optical and infrared: LSST and Euclid, based on an N-body simulation+semi-analytical cone with a posterior modification with \texttt{PhotReal}. This technique modifies the original photometry by using an empirical library of spectral templates to make it more realistic. The reliability of the catalogues is confirmed by comparing the obtained color-magnitude relation, the luminosity and mass function and the angular correlation function with those of real data. Consistent comparisons between the expected photometric redshifts for different surveys are also provided. Very deep near infrared surveys such as Euclid will provide very good performance ($\Delta z/(1+z) \sim 0.025-0.053$) down to $H\sim24$ AB mag and up to $z\sim3$ depending on the optical observations available from the ground whereas extremely deep optical surveys such as LSST will obtain an overall lower photometric redshift resolution ($\Delta z/(1+z) \sim 0.045$) down to $i\sim27.5$ AB mag, being considerably improved ($\Delta z/(1+z) \sim 0.035$) if we restrict the sample down to i$\sim$24 AB mag. Those numbers can be substantially upgraded by selecting a subsample of galaxies with the best quality photometric redshifts. We finally discuss the impact that these surveys will have for the community in terms of photometric redshift legacy. This is the first of a series of papers where we set a framework for comparability between mock catalogues and observations with a particular focus on cluster surveys. The Euclid and LSST mocks are made publicly available in the following link: http://photmocks.obspm.fr/.Comment: accepted in MNRAS. Mocks available in the following link: http://photmocks.obspm.fr

II. Apples to apples A2A^2: cluster selection functions for next-generation surveys

We present the cluster selection function for three of the largest next-generation stage-IV surveys in the optical and infrared: Euclid-Optimistic, Euclid-Pessimistic and the Large Synoptic Survey Telescope (LSST). To simulate these surveys, we use the realistic mock catalogues introduced in the first paper of this series. We detected galaxy clusters using the Bayesian Cluster Finder (BCF) in the mock catalogues. We then modeled and calibrated the total cluster stellar mass observable-theoretical mass ($M^*_{\rm CL}-M_{\rm h}$) relation using a power law model, including a possible redshift evolution term. We find a moderate scatter of $\sigma_{M^*_{\rm CL} | M_{\rm h}}$ of 0.124, 0.135 and 0.136 $\rm dex$ for Euclid-Optimistic, Euclid-Pessimistic and LSST, respectively, comparable to other work over more limited ranges of redshift. Moreover, the three datasets are consistent with negligible evolution with redshift, in agreement with observational and simulation results in the literature. We find that Euclid-Optimistic will be able to detect clusters with $>80\%$ completeness and purity down to $8\times10^{13} h^{-1} M_{\odot}$ up to $z<1$. At higher redshifts, the same completeness and purity are obtained with the larger mass threshold of $2\times10^{14} h^{-1} M_{\odot}$ up to $z=2$. The Euclid-Pessimistic selection function has a similar shape with $\sim10\%$ higher mass limit. LSST shows $\sim 5\%$ higher mass limit than Euclid-Optimistic up to $z<0.7$ and increases afterwards, reaching values of $2\times10^{14} h^{-1} M_{\odot}$ at $z=1.4$. Similar selection functions with only $80\%$ completeness threshold have been also computed. The complementarity of these results with selection functions for surveys in other bands is discussed.Comment: 13 pages, 10 figures, accepted for publication in MNRA

The ACS Virgo Cluster Survey. XVII. The Spatial Alignment of Globular Cluster Systems With Early-Type Host Galaxies

We study the azimuthal distribution of globular clusters (GCs) in early-type galaxies and compare them to their host galaxies using data from the ACS Virgo Cluster Survey. We find that in host galaxies with visible elongation (epsilon > 0.2) and intermediate to high luminosities (M_z<-19), the GCs are preferentially aligned along the major axis of the stellar light. The red (metal-rich) GC subpopulations show strong alignment with the major axis of the host galaxy, which supports the notion that these GCs are associated with metal-rich field stars. The metal-rich GCs in lenticular galaxies show signs of being more strongly associated with disks rather than bulges. Surprisingly, we find that the blue (metal-poor) GCs can also show the same correlation. If the metal-poor GCs are part of the early formation of the halo and built up through mergers, then our results support a picture where halo formation and merging occur anisotropically, and where the present day major axis is an indicator of the preferred merging axis.Comment: 8 pages, 7 figures, accepted for publication in The Astrophysical Journa

The RedGOLD cluster detection algorithm and its cluster candidate catalogue for the CFHT-LS W1

We present RedGOLD (Red-sequence Galaxy Overdensity cLuster Detector), a new optical/NIR galaxy cluster detection algorithm, and apply it to the CFHT-LS W1 field. RedGOLD searches for red-sequence galaxy overdensities while minimizing contamination from dusty star-forming galaxies. It imposes an Navarro–Frenk–White profile and calculates cluster detection significance and richness. We optimize these latter two parameters using both simulations and X-ray-detected cluster catalogues, and obtain a catalogue ∼80 per cent pure up to z ∼ 1, and ∼100 per cent (∼70 per cent) complete at z ≤ 0.6 (z ≲ 1) for galaxy clusters with M ≳ 10^(14) M_⊙ at the CFHT-LS Wide depth. In the CFHT-LS W1, we detect 11 cluster candidates per deg^2 out to z ∼ 1.1. When we optimize both completeness and purity, RedGOLD obtains a cluster catalogue with higher completeness and purity than other public catalogues, obtained using CFHT-LS W1 observations, for M ≳ 10^(14) M_⊙. We use X-ray-detected cluster samples to extend the study of the X-ray temperature–optical richness relation to a lower mass threshold, and find a mass scatter at fixed richness of σ_(lnM|λ) = 0.39 ± 0.07 and σ_(lnM|λ) = 0.30 ± 0.13 for the Gozaliasl et al. and Mehrtens et al. samples. When considering similar mass ranges as previous work, we recover a smaller scatter in mass at fixed richness. We recover 93 per cent of the redMaPPer detections, and find that its richness estimates is on average ∼40–50 per cent larger than ours at z > 0.3. RedGOLD recovers X-ray cluster spectroscopic redshifts at better than 5 per cent up to z ∼ 1, and the centres within a few tens of arcseconds

Understanding the Unique Assembly History of Central Group Galaxies

Central Galaxies (CGs) in massive halos live in unique environments with formation histories closely linked to that of the host halo. In local clusters they have larger sizes ($R_e$) and lower velocity dispersions (sigma) at fixed stellar mass M_star, and much larger R_e at a fixed $\sigma$ than field and satellite galaxies (non-CGs). Using spectroscopic observations of group galaxies selected from the COSMOS survey, we compare the dynamical scaling relations of early-type CGs and non-CGs at z~0.6, to distinguish possible mechanisms that produce the required evolution. CGs are systematically offset towards larger R_e at fixed $\sigma$ compared to non-CGs with similar M_star. The CG R_e-M_star relation also shows differences, primarily driven by a sub-population (~15%) of galaxies with large $R_e$, while the M_star-sigma relations are indistinguishable. These results are accentuated when double Sersic profiles, which better fit light in the outer regions of galaxies, are adopted. They suggest that even group-scale CGs can develop extended components by these redshifts that can increase total $R_e$ and M_star estimates by factors of ~2. To probe the evolutionary link between our sample and cluster CGs, we also analyze two cluster samples at z~0.6 and z~0. We find similar results for the more massive halos at comparable z, but much more distinct CG scaling relations at low-z. Thus, the rapid, late-time accretion of outer components, perhaps via the stripping and accretion of satellites, would appear to be a key feature that distinguishes the evolutionary history of CGs.Comment: 18 pages, 14 Figures, ApJ in pres

The Next Generation Virgo Cluster Survey-Infrared (NGVS-IR). I. A New Near-Ultraviolet, Optical, and Near-Infrared Globular Cluster Selection Tool

The NGVS-IR project (Next Generation Virgo Cluster Survey-Infrared) is a contiguous, near-infrared imaging survey of the Virgo cluster of galaxies. It complements the optical wide-field survey of Virgo (NGVS). In its current state, NGVS-IR consists of K_s -band imaging of 4 deg^2 centered on M87 and J- and K_s -band imaging of ~16 deg^2 covering the region between M49 and M87. We present observations of the central 4 deg^2 centered on Virgo's core region. The data were acquired with WIRCam on the Canada-France-Hawaii Telescope, and the total integration time was 41 hr distributed over 34 contiguous tiles. A survey-specific strategy was designed to account for extended galaxies while still measuring accurate sky brightness within the survey area. The average 5σ limiting magnitude is K_s = 24.4 AB mag, and the 50% completeness limit is K_s = 23.75 AB mag for point-source detections, when using only images with better than 0."7 seeing (median seeing 0."54). Star clusters are marginally resolved in these image stacks, and Virgo galaxies with µ_K_s ≃ 24.4 AB mag arcsec^(–2) are detected. Combining the K_s data with optical and ultraviolet data, we build the uiK_s color-color diagram, which allows a very clean color-based selection of globular clusters in Virgo. This diagnostic plot will provide reliable globular cluster candidates for spectroscopic follow-up campaigns, needed to continue the exploration of Virgo's photometric and kinematic substructures, and will help the design of future searches for globular clusters in extragalactic systems. We show that the new uiK_s diagram displays significantly clearer substructure in the distribution of stars, globular clusters, and galaxies than the gzK_s diagram—the NGVS + NGVS-IR equivalent of the BzK diagram that is widely used in cosmological surveys. Equipped with this powerful new tool, future NGVS-IR investigations based on the uiK_s diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies

The ACS Virgo Cluster Survey II. Data Reduction Procedures

The ACS Virgo Cluster Survey is a large program to carry out multi-color imaging of 100 early-type members of the Virgo Cluster using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope. Deep F475W and F850LP images (~ SDSS g and z) are being used to study the central regions of the program galaxies, their globular cluster systems, and the three-dimensional structure of Virgo itself. In this paper, we describe in detail the data reduction procedures used for the survey, including image registration, drizzling strategies, the computation of weight images, object detection, the identification of globular cluster candidates, and the measurement of their photometric and structural parameters.Comment: 33 pages, 8 figures. Accepted for publication in ApJS. Also available at http://www.physics.rutgers.edu/~pcote/acs/publications.htm

Environmental dependence of bulge-dominated galaxy sizes in hierarchical models of galaxy formation. Comparison with the local Universe

We compare state-of-the-art semi-analytic models of galaxy formation as well as advanced sub-halo abundance matching models with a large sample of early-type galaxies from SDSS at z < 0.3. We focus our attention on the dependence of median sizes of central galaxies on host halo mass. The data do not show any difference in the structural properties of early-type galaxies with environment, at fixed stellar mass. All hierarchical models considered in this work instead tend to predict a moderate to strong environmental dependence, with the median size increasing by a factor of about 1.5-3 when moving from low to high mass host haloes. At face value the discrepancy with the data is highly significant, especially at the cluster scale, for haloes above log Mhalo > 14. The convolution with (correlated) observational errors reduces some of the tension. Despite the observational uncertainties, the data tend to disfavour hierarchical models characterized by a relevant contribution of disc instabilities to the formation of spheroids, strong gas dissipation in (major) mergers, short dynamical friction timescales, and very short quenching timescales in infalling satellites. We also discuss a variety of additional related issues, such as the slope and scatter in the local size-stellar mass relation, the fraction of gas in local early-type galaxies, and the general predictions on satellite galaxies.Comment: 27 pages, 14 figures, 2 tables. MNRAS, in pres

Trends in the Globular Cluster Luminosity Function of Early-Type Galaxies

We present results from a study of the globular cluster luminosity function (GCLF) in a sample of 89 early-type galaxies observed as part of the ACS Virgo Cluster Survey. Using a Gaussian parametrization of the GCLF, we find a highly significant correlation between the GCLF dispersion, sigma, and the galaxy luminosity, M_B, in the sense that the GC systems in fainter galaxies have narrower luminosity functions. The GCLF dispersions in the Milky Way and M31 are fully consistent with this trend, implying that the correlation between sigma and galaxy luminosity is more fundamental than older suggestions that GCLF shape is a function of galaxy Hubble type. We show that the sigma - M_B relation results from a bonafide narrowing of the distribution of (logarithmic) cluster masses in fainter galaxies. We further show that this behavior is mirrored by a steepening of the GC mass function for relatively high masses, M >~ 3 x 10^5 M_sun, a mass regime in which the shape of the GCLF is not strongly affected by dynamical evolution over a Hubble time. We argue that this trend arises from variations in initial conditions and requires explanation by theories of cluster formation. Finally, we confirm that in bright galaxies, the GCLF "turns over" at the canonical mass scale of M_TO ~ 2 x 10^5 M_sun. However, we find that M_TO scatters to lower values (~1-2 x 10^5 M_sun) in galaxies fainter than M_B >~ -18.5, an important consideration if the GCLF is to be used as a distance indicator for dwarf ellipticals.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letters. Also available at http://www.cadc.hia.nrc.gc.ca/community/ACSVCS/publications.htm

The ACS Virgo Cluster Survey XV. The Formation Efficiencies of Globular Clusters in Early-Type Galaxies: The Effects of Mass and Environment

The fraction of stellar mass contained in globular clusters (GCs), also measured by number as the specific frequency, is a fundamental quantity that reflects both a galaxy's early star formation and its entire merging history. We present specific frequencies, luminosities, and mass fractions for the globular cluster systems of 100 early-type galaxies in the ACS Virgo Cluster Survey, the largest homogeneous catalog of its kind. We find that 1) GC mass fractions can be high in both giants and dwarfs, but are universally low in galaxies with intermediate luminosities. 2) The behavior of specific frequency across galaxy mass is dominated by the blue GCs. 3) The GC fractions of low-mass galaxies exhibit a dependence on environment. Nearly all dwarf galaxies with high GC fractions are within 1 Mpc of the cD galaxy M87, presenting the first strong evidence that GC formation in dwarfs is biased toward dense environments. 4) GC formation in central dwarfs is biased because their stars form earliest and most intensely. Comparisons to the Millennium Simulation show that central dwarfs have older stellar populations and form more stars at higher star formation rates (SFRs) and SFR surface densities. The SFR surface density in simulated dwarfs peaks before the total SFR, naturally producing GC populations that are older and more metal-poor than the field stars. 5) Dwarfs within ~40 kpc of the giant ellipticals M87 and M49 are red and have few or no GCs, suggesting that they have been tidally stripped and have contributed their GCs to the halos of their giant neighbors. The central dwarfs with high GC mass fractions are thus likely to be the survivors most similar to the protogalaxies that assembled the rich M87 globular cluster system.(Abridged)Comment: 27 pages, 21 figures, 7 tables. Accepted for publication in the Astrophysical Journa