Jean-Charles Cuillandre

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (75)224.67 Total impact

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    ABSTRACT: The Next Generation Virgo Cluster Survey has recently determined the luminosity function of galaxies in the core of the Virgo cluster down to unprecedented magnitude and surface brightness limits. Comparing simulations of cluster formation to the derived central stellar mass function, we attempt to estimate the stellar-to-halo-mass ratio (SHMR) for dwarf galaxies, as it would have been before they fell into the cluster. This approach ignores several details and complications, e.g., the contribution of ongoing star formation to the present-day stellar mass of cluster members, and the effects of adiabatic contraction and/or violent feedback on the subhalo and cluster potentials. The final results are startlingly simple, however; we find that the trends in the SHMR determined previously for bright galaxies appear to extend down in a scale-invariant way to the faintest objects detected in the survey. These results extend measurements of the formation efficiency of field galaxies by two decades in halo mass, or five decades in stellar mass, down to some of the least massive dwarf galaxies known, with stellar masses of $\sim 10^5 M_\odot$.
    The Astrophysical Journal 07/2015; 807(1). DOI:10.1088/0004-637X/807/1/88 · 6.28 Impact Factor
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    ABSTRACT: We report the discovery of three large (R29 >~ 1 arcminute) extremely low surface brightness (mu_(V,0) ~ 27.0) galaxies identified using our deep, wide-field imaging of the Virgo Cluster from the Burrell Schmidt telescope. Complementary data from the Next Generation Virgo Cluster Survey do not resolve red giant branch stars in these objects down to i=24, yielding a lower distance limit of 2.5 Mpc. At the Virgo distance, these objects have half-light radii 3-10 kpc and luminosities L_V=2-9x10^7 Lsun. These galaxies rival the most extreme LSB galaxies recently identified in the Coma cluster and are located well within Virgo's virial radius; two are projected directly on the cluster core. One object appears to be a nucleated LSB in the process of being tidally stripped to form a new Virgo ultracompact dwarf galaxy. The others show no sign of tidal disruption, despite the fact that such objects should be most vulnerable to tidal destruction in the cluster environment. The relative proximity of Virgo makes these objects amenable to detailed studies of their structural properties and stellar populations. They thus provide an important new window onto the connection between cluster environment and galaxy evolution at the extremes.
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    ABSTRACT: Context. The elliptical galaxy NGC 3923 is known to be surrounded by a number of stellar shells, a probable remnant of an accreted galaxy. Despite its uniqueness, the deepest images of its outskirts come from the 80s. B\'{i}lek et al. (2014) predicted a new shell to lie in this region on the basis of the MOND theory of modified dynamics. Aims. To obtain the deepest image ever of the galaxy and to map the tidal features in it. Methods. The image of the galaxy was taken by the MegaCam camera at the Canada-France-Hawaii Telescope in the $g'$ band. It reached the surface-brightness limit of 29 mag arcsec$^{-2}$. Moreover, we reanalyze an archival HST image of the galaxy. Results. We detected up to 42 shells in NGC 3923. This is by far most of all galaxies. We present the description of the shells and other tidal features in the galaxy. A probable progenitor of some of these features was discovered. The shell system likely originates from two or more progenitors. The predicted shell was not detected, but we found that the prediction was based on incorrect assumptions and poor data.
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    ABSTRACT: NGC 4203 is a nearby early-type galaxy surrounded by a very large, low-column-density HI disc. In this paper we study the star formation efficiency in the gas disc of NGC 4203 by using the UV, deep optical imaging and infrared data. We confirm that the HI disc consists of two distinct components: an inner star forming ring with radius from $\sim$ 1 to $\sim$ 3 R$_{eff}$, and an outer disc. The outer HI disc is 9 times more massive than the inner HI ring. At the location of the inner HI ring we detect spiral-like structure both in the deep $g'-r'$ image and in the 8 $\mu$m $Spitzer$-IRAC image, extending in radius up to $\sim$ 3 R$_{eff}$. These two gas components have a different star formation efficiency likely due to the different metallicity and dust content. The inner component has a star formation efficiency very similar to the inner regions of late-type galaxies. Although the outer component has a very low star formation efficiency, it is similar to that of the outer regions of spiral galaxies and dwarfs. We suggest that these differences can be explained with different gas origins for the two components such as stellar mass loss for the inner HI ring and accretion from the inter galactic medium (IGM) for the outer HI disc. The low level star formation efficiency in the outer HI disc is not enough to change the morphology of NGC 4203, making the depletion time of the HI gas much too long.
    Monthly Notices of the Royal Astronomical Society 05/2015; 451(1). DOI:10.1093/mnras/stv992 · 5.23 Impact Factor
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    ABSTRACT: We present Gemini GMOS-IFU data of eight compact low-mass early-type galaxies (ETGs) in the Virgo cluster. We analyse their stellar kinematics, stellar population, and present two-dimensional maps of these properties covering the central 5"x 7" region. We find a large variety of kinematics: from non- to highly-rotating objects, often associated with underlying disky isophotes revealed by deep images from the Next Generation Virgo Cluster Survey. In half of our objects, we find a centrally-concentrated younger and more metal-rich stellar population. We analyze the specific stellar angular momentum through the lambdaR parameter and find six fast-rotators and two slow-rotators, one having a thin counter-rotating disk. We compare the local galaxy density and stellar populations of our objects with those of 39 more extended low-mass Virgo ETGs from the SMAKCED survey and 260 massive ($M>10^{10}$\Msun) ETGs from the A3D sample. The compact low-mass ETGs in our sample are located in high density regions, often close to a massive galaxy and have, on average, older and more metal-rich stellar populations than less compact low-mass galaxies. We find that the stellar population parameters follow lines of constant velocity dispersion in the mass-size plane, smoothly extending the comparable trends found for massive ETGs. Our study supports a scenario where low-mass compact ETGs have experienced long-lived interactions with their environment, including ram-pressure stripping and gravitational tidal forces, that may be responsible for their compact nature.
    The Astrophysical Journal 04/2015; 804(1). DOI:10.1088/0004-637X/804/1/70 · 6.28 Impact Factor
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    ABSTRACT: The origin of ultra-compact dwarfs (UCDs)--objects larger and more massive than typical globular clusters (GCs), but more compact than typical dwarf galaxies--has been hotly debated in the 15 years since their discovery. Even whether UCDs should be considered galactic in origin, or simply the most extreme GCs, is not yet settled. We present the dynamical properties of 97 spectroscopically confirmed UCDs (rh >~10 pc) and 911 GCs associated with central cD galaxy of the Virgo cluster, M87. Our UCDs, of which 89% have M_star > ~2X10^6 M_sun and 92% are as blue as the classic blue GCs, nearly triple the sample of previous confirmed Virgo UCDs, providing by far the best opportunity for studying the global dynamics of a UCD system. We found that (1) UCDs have a surface number density profile that is shallower than that of the blue GCs in the inner ~ 70 kpc and as steep as that of the red GCs at larger radii; (2) UCDs exhibit a significantly stronger rotation than the GCs, and the blue GCs seem to have a velocity field that is more consistent with that of the surrounding dwarf ellipticals than with that of UCDs; (3) UCDs have a radially increasing orbital anisotropy profile, and are tangentially-biased at radii < ~ 40 kpc and radially-biased further out. In contrast, the blue GCs become more tangentially-biased at larger radii beyond ~ 40 kpc; (4) GCs with M_star > 2X10^6 M_sun have rotational properties indistinguishable from the less massive ones, suggesting that it is the size, instead of mass, that differentiates UCDs from GCs as kinematically distinct populations. We conclude that most UCDs in M87 are not consistent with being merely the most luminous and extended examples of otherwise normal GCs. The radially-biased orbital structure of UCDs at large radii is in general agreement with the "tidally threshed dwarf galaxy" scenario.
    The Astrophysical Journal 01/2015; 802(1). DOI:10.1088/0004-637X/802/1/30 · 6.28 Impact Factor
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    ABSTRACT: Galactic archeology based on star counts is instrumental to reconstruct the past mass assembly of Local Group galaxies. The development of new observing techniques and data-reduction, coupled with the use of sensitive large field of view cameras, now allows us to pursue this technique in more distant galaxies exploiting their diffuse low surface brightness (LSB) light. As part of the Atlas3D project, we have obtained with the MegaCam camera at the Canada-France Hawaii Telescope extremely deep, multi--band, images of nearby early-type galaxies. We present here a catalog of 92 galaxies from the Atlas3D sample, that are located in low to medium density environments. The observing strategy and data reduction pipeline, that achieve a gain of several magnitudes in the limiting surface brightness with respect to classical imaging surveys, are presented. The size and depth of the survey is compared to other recent deep imaging projects. The paper highlights the capability of LSB--optimized surveys at detecting new prominent structures that change the apparent morphology of galaxies. The intrinsic limitations of deep imaging observations are also discussed, among those, the contamination of the stellar halos of galaxies by extended ghost reflections, and the cirrus emission from Galactic dust. The detection and systematic census of fine structures that trace the present and past mass assembly of ETGs is one of the prime goals of the project. We provide specific examples of each type of observed structures -- tidal tails, stellar streams and shells --, and explain how they were identified and classified. We give an overview of the initial results. The detailed statistical analysis will be presented in future papers.
    Monthly Notices of the Royal Astronomical Society 10/2014; 446(1). DOI:10.1093/mnras/stu2019 · 5.23 Impact Factor
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    ABSTRACT: Our proximity and external vantage point make M31 an ideal testbed for understanding the structure of spiral galaxies. The Andromeda Optical and Infrared Disk Survey (ANDROIDS) has mapped M31's bulge and disk out to R=40 kpc in $ugriJK_s$ bands with CFHT using a careful sky calibration. We use Bayesian modelling of the optical-infrared spectral energy distribution (SED) to estimate profiles of M31's stellar populations and mass along the major axis. This analysis provides evidence for inside-out disk formation and a declining metallicity gradient. M31's $i$-band mass-to-light ratio ($M/L_i^*$) decreases from 0.5 dex in the bulge to $\sim 0.2$ dex at 40 kpc. The best-constrained stellar population models use the full $ugriJK_s$ SED but are also consistent with optical-only fits. Therefore, while NIR data can be successfully modelled with modern stellar population synthesis, NIR data do not provide additional constraints in this application. Fits to the $gi$-SED alone yield $M/L_i^*$ that are systematically lower than the full SED fit by 0.1 dex. This is still smaller than the 0.3 dex scatter amongst different relations for $M/L_i$ via $g-i$ colour found in the literature. We advocate a stellar mass of $M_*(30\mathrm{kpc})=10.3^{+2.3}_{-1.7}\times 10^{10}\mathrm{M}_\odot$ for the M31 bulge and disk.
    Proceedings of the International Astronomical Union 09/2014; 10(S311). DOI:10.1017/S1743921315003440
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    ABSTRACT: We report on a large-scale study of the distribution of globular clusters (GCs) throughout the Virgo cluster, based on photometry from the Next Generation Virgo Cluster Survey, a large imaging survey covering Virgo's primary subclusters to their virial radii. Using the g', (g'-i') color-magnitude diagram of unresolved and marginally-resolved sources, we constructed 2-D maps of the GC distribution. We present the clearest evidence to date showing the difference in concentration between red and blue GCs over the extent of the cluster, where the red (metal-rich) GCs are largely located around the massive early-type galaxies, whilst the blue (metal-poor) GCs have a more extended spatial distribution, with significant populations present beyond 83' (215 kpc) along the major axes of M49 and M87. The GC distribution around M87 and M49 shows remarkable agreement with the shape, ellipticity and boxiness of the diffuse light surrounding both galaxies. We find evidence for spatial enhancements of GCs surrounding M87 that may be indicative of recent interactions or an ongoing merger history. We compare the GC map to the locations of Virgo galaxies and the intracluster X-ray gas, and find good agreement between these baryonic structures. The Virgo cluster contains a total population of 67300$\pm$14400 GCs, of which 35% are located in M87 and M49 alone. We compute a cluster-wide specific frequency S_N,CL=$2.8\pm0.7$, including Virgo's diffuse light. The GC-to-baryonic mass fraction is e_b=$5.7\pm1.1\times10^{-4} $and the GC-to-total cluster mass formation efficiency is e_t=$2.9\pm0.5\times10^{-5}$, values slightly lower than, but consistent with, those derived for individual galactic halos. Our results show that the production of the complex structures in the unrelaxed Virgo cluster core (including the diffuse intracluster light) is an ongoing process.(abridged)
    The Astrophysical Journal 08/2014; 794(2). DOI:10.1088/0004-637X/794/2/103 · 6.28 Impact Factor
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    ABSTRACT: We aim at characterizing the accretion properties of several hundred members of the star-forming cluster NGC 2264 (3 Myr). We performed a deep u,g,r,i mapping and a simultaneous u+r monitoring of the region with CFHT/MegaCam in order to directly probe the accretion process from UV excess measurements. Photometric properties and stellar parameters are determined homogeneously for about 750 monitored young objects, spanning the mass range 0.1-2 Mo. About 40% are classical (accreting) T Tauri stars, based on various diagnostics (H_alpha, UV and IR excesses). The remaining non-accreting members define the (photospheric+chromospheric) reference UV emission level over which flux excess is detected and measured. We revise the membership status of cluster members based on UV accretion signatures and report a new population of 50 CTTS candidates. A large range of UV excess is measured for the CTTS population, varying from a few 0.1 to 3 mag. We convert these values to accretion luminosities and obtain mass accretion rates ranging from 1e-10 to 1e-7 Mo/yr. Taking into account a mass-dependent detection threshold for weakly accreting objects, we find a >6sigma correlation between mass accretion rate and stellar mass. A power-law fit, properly accounting for upper limits, yields M_acc $\propto$ M^{1.4+/-0.3}. At any given stellar mass, we find a large spread of accretion rates, extending over about 2 orders of magnitude. The monitoring of the UV excess on a timescale of a couple of weeks indicates that its variability typically amounts to 0.5 dex, much smaller than the observed spread. We suggest that a non-negligible age spread across the cluster may effectively contribute to the observed spread in accretion rates at a given mass. In addition, different accretion mechanisms (like, e.g., short-lived accretion bursts vs. more stable funnel-flow accretion) may be associated to different M_acc regimes.
    Astronomy and Astrophysics 08/2014; 570. DOI:10.1051/0004-6361/201423776 · 4.48 Impact Factor
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    ABSTRACT: We study the dynamics of the giant elliptical galaxy M87 from the central to the outermost regions with the made-to-measure (M2M) method. We use a new catalogue of 922 globular cluster line-of- sight velocities extending to a projected radius of 180 kpc (equivalent to 25 M87 effective radii), and SAURON integral field unit data within the central 2.4 kpc. 263 globular clusters, mainly located beyond 40 kpc, are newly observed by the Next Generation Virgo Survey (NGVS). For the M2M modelling, the gravitational potential is taken as a combination of a luminous matter potential with a constant stellar mass-to-light ratio and a dark matter potential modelled as a logarithmic potential. Our best dynamical model returns a stellar mass-to-light ratio in the I band of M/LI = 6.0(+ -0.3) M_sun/L_sun with a dark matter potential scale velocity of 591(+ -50) km/s and scale radius of 42(+ -10) kpc. We determine the total mass of M87 within 180 kpc to be (1.5 + - 0.2) 10^13 M_sun. The mass within 40 kpc is smaller than previous estimates determined using globular cluster kinematics that did not extend beyond 45 kpc. With our new globular cluster velocities at much larger radii, we see that globular clusters around 40 kpc show an anomalously large velocity dispersion which affected previous results. The mass we derived is in good agreement with that inferred from ROSAT X-ray observation out to 180 kpc. Within 30 kpc our mass is also consistent with that inferred from Chandra and XMM-Newton X-ray observations, while within 120 kpc it is about 20% smaller. The model velocity dispersion anisotropy beta parameter for the globular clusters in M87 is small, varying from -0.2 at the centre to 0.2 at 40 kpc, and gradually decreasing to zero at 120 kpc.
    The Astrophysical Journal 07/2014; 792(1). DOI:10.1088/0004-637X/792/1/59 · 6.28 Impact Factor
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    ABSTRACT: It has recently been proposed that the dwarf spheroidal galaxies located in the Local Group disks of satellites (DoSs) may be tidal dwarf galaxies (TDGs) born in a major merger at least 5 Gyr ago. Whether TDGs can live that long is still poorly constrained by observations. As part of deep optical and HI surveys with the CFHT MegaCam camera and Westerbork Synthesis Radio Telescope made within the ATLAS3D project, and follow-up spectroscopic observations with the Gemini-North telescope, we have discovered old TDG candidates around several early-type galaxies. At least one of them has an oxygen abundance close to solar, as expected for a tidal origin. This confirmed pre-enriched object is located within the gigantic, but very low surface brightness, tidal tail that emanates from the elliptical galaxy, NGC 5557. An age of 4 Gyr estimated from its SED fitting makes it the oldest securely identified TDG ever found so far. We investigated the structural and gaseous properties of the TDG and of a companion located in the same collisional debris, and thus most likely of tidal origin as well. Despite several Gyr of evolution close to their parent galaxies, they kept a large gas reservoir. Their central surface brightness is low and their effective radius much larger than that of typical dwarf galaxies of the same mass. This possibly provides us with criteria to identify tidal objects which can be more easily checked than the traditional ones requiring deep spectroscopic observations. In view of the above, we discuss the survival time of TDGs and question the tidal origin of the DoSs.
    Monthly Notices of the Royal Astronomical Society 03/2014; 440(2). DOI:10.1093/mnras/stu330 · 5.23 Impact Factor
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    ABSTRACT: The NGVS-IR project (Next Generation Virgo 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). The current state of NGVS-IR consists of Ks-band imaging of 4 deg^2 centered on M87, and J and Ks-band imaging of 16 deg^2 covering the region between M49 and M87. In this paper, we present the 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 hours distributed in 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 5\sigma limiting magnitude is Ks=24.4 AB mag and the 50% completeness limit is Ks=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 \mu_Ks=24.4 AB mag arcsec^-2 are detected. Combining the Ks data with optical and ultraviolet data, we build the uiK 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 sub-structures, and will help the design of future searches for globular clusters in extragalactic systems. Equipped with this powerful new tool, future NGVS-IR investigations based on the uiK diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies.
    The Astrophysical Journal Supplement Series 01/2014; 210:4. · 14.14 Impact Factor
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    ABSTRACT: 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 Ks-band imaging of 4 deg2 centered on M87 and J- and Ks-band imaging of ~16 deg2 covering the region between M49 and M87. We present observations of the central 4 deg2 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 Ks = 24.4 AB mag, and the 50% completeness limit is Ks = 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 AB mag arcsec–2 are detected. Combining the Ks data with optical and ultraviolet data, we build the uiKs 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 uiKs diagram displays significantly clearer substructure in the distribution of stars, globular clusters, and galaxies than the gzKs 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 uiKs diagram will address the mapping and analysis of extended structures and compact stellar systems in and around Virgo galaxies.
    The Astrophysical Journal Supplement Series 01/2014; 210(1):4. DOI:10.1088/0067-0049/210/1/4 · 14.14 Impact Factor
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    Jonathan Sick · Stéphane Courteau · Jean-Charles Cuillandre
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    ABSTRACT: The Andromeda Optical and Infrared Disk Survey has mapped M31 in $u^* g^\prime r^\prime i^\prime J K_s$ wavelengths out to R=40 kpc using the MegaCam and WIRCam wide-field cameras on the Canada-France-Hawaii Telescope. Our survey is uniquely designed to simultaneously resolve stars while also carefully reproducing the surface brightness of M31, allowing us to study M31's global structure in the context of both resolved stellar populations and spectral energy distributions. We use the Elixir-LSB method to calibrate the optical $u^* g^\prime r^\prime i^\prime$ images by building real-time maps of the sky background with sky-target nodding. These maps are stable to $\mu_g \lesssim 28.5$ mag arcsec$^{-2}$ and reveal warps in the outer M31 disk in surface brightness. The equivalent WIRCam mapping in the near-infrared uses a combination of sky-target nodding and image-to-image sky offset optimization to produce stable surface brightnesses. This study enables a detailed analysis of the systematics of spectral energy distribution fitting with near-infrared bands where asymptotic giant branch stars impose a significant, but ill-constrained, contribution to the near-infrared light of a galaxy. Here we present panchromatic surface brightness maps and initial results from our near-infrared resolved stellar catalog.
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    ABSTRACT: We report the discovery of 2010 GB$_{174}$, a likely new member of the Inner Oort Cloud (IOC). 2010 GB$_{174}$ is one of 91 Trans Neptunian Objects (TNOs) and Centaurs discovered in a 76 deg$^2$ contiguous region imaged as part of the Next Generation Virgo Cluster Survey (NGVS) --- a moderate ecliptic latitude survey reaching a mean limiting magnitude of $g^\prime \simeq 25.5$ --- using MegaPrime on the 3.6m Canada France Hawaii Telescope. 2010 GB$_{174}$ is found to have an orbit with semi-major axis $a\simeq350.8$ AU, inclination $i \simeq 21.6^\circ$ and pericentre $q\sim48.5$ AU. This is the second largest perihelion distance among known solar system objects. Based on the sky coverage and depth of the NGVS, we estimate the number of IOC members with sizes larger than 300 km ($H_V \le 6.2$ mag) to be $\simeq 11\,000$. A comparison of the detection rate from the NGVS and the PDSSS (a characterized survey that `re-discovered' the IOC object Sedna) gives, for an assumed a power-law LF for IOC objects, a slope of $\alpha \simeq 0.7 \pm 0.2$, with only two detections in this region this slope estimate is highly uncertain.
    The Astrophysical Journal Letters 08/2013; 775(1). DOI:10.1088/2041-8205/775/1/L8 · 5.60 Impact Factor
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    ABSTRACT: We present wide-field near-infrared J and Ks images of the Andromeda Galaxy taken with WIRCam on the Canada-France-Hawaii Telescope (CFHT) as part of the Andromeda Optical and Infrared Disk Survey (ANDROIDS). This data set allows simultaneous observations of resolved stars and NIR surface brightness across M31's entire bulge and disk (within R=22 kpc). The primary concern of this work is the development of NIR observation and reduction methods to recover a uniform surface brightness map across the 3x1 degree disk of M31. This necessitates sky-target nodding across 27 WIRCam fields. Two sky-target nodding strategies were tested, and we find that strictly minimizing sky sampling latency does not maximize sky subtraction accuracy, which is at best 2% of the sky level. The mean surface brightness difference between blocks in our mosaic can be reduced from 1% to 0.1% of the sky brightness by introducing scalar sky offsets to each image. The true surface brightness of M31 can be known to within a statistical zeropoint of 0.15% of the sky level (0.2 mag arcsec sq. uncertainty at R=15 kpc). Surface brightness stability across individual WIRCam frames is limited by both WIRCam flat field evolution and residual sky background shapes. To overcome flat field variability of order 1% over 30 minutes, we find that WIRCam data should be calibrated with real-time sky flats. Due either to atmospheric or instrumental variations, the individual WIRCam frames have typical residual shapes with amplitudes of 0.2% of the sky after real-time flat fielding and median sky subtraction. We present our WIRCam reduction pipeline and performance analysis here as a template for future near-infrared observers needing wide-area surface brightness maps with sky-target nodding, and give specific recommendations for improving photometry of all CFHT/WIRCam programs. (Abridged)
    The Astronomical Journal 03/2013; 147(5). DOI:10.1088/0004-6256/147/5/109 · 4.05 Impact Factor
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    ABSTRACT: We present an investigation into the origins of a series of interlaced narrow filamentary stellar structures, loops and plumes in the vicinity of the Virgo Cluster, edge-on spiral galaxy, NGC 4216 that were previously identified by the Blackbird Telescope. Using the deeper, higher-resolution and precisely calibrated optical CFHT/MegaCam images obtained as part of the Next Generation Virgo Cluster Survey (NGVS), we confirm the previously identified features and identify a few additional structures. The NGVS data allowed us to make a physical study of these low-surface brightness features and investigate their origin. The likely progenitors of the structures were identified as either already catalogued VCC dwarfs or newly discovered satellites caught in the act of being destroyed. They have the same g-i color index and likely contain similar stellar populations. The alignment of three dwarfs along an apparently single stream is intriguing, and we cannot totally exclude that these are second-generation dwarf galaxies being born inside the filament from the debris of an original dwarf. The observed complex structures, including in particular a stream apparently emanating from a satellite of a satellite, point to a high rate of ongoing dwarf destruction/accretion in the region of the Virgo Cluster where NGC 4216 is located. We discuss the age of the interactions and whether they occurred in a group that is just falling into the cluster and shows signs of so-called "pre-processing" before it gets affected by the cluster environment, or in a group which already ventured towards the central regions of Virgo Cluster.
    The Astrophysical Journal 02/2013; 767(2). DOI:10.1088/0004-637X/767/2/133 · 6.28 Impact Factor
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    ABSTRACT: We report the discovery of a giant HI tail in the intra-group medium of HCG 44 as part of the Atlas3D survey. The tail is ~300 kpc long in projection and contains ~5x10^8 M_sun of HI. We detect no diffuse stellar light at the location of the tail down to ~28.5 mag/arcsec^2 in g band. We speculate that the tail might have formed as gas was stripped from the outer regions of NGC 3187 (a member of HCG 44) by the group tidal field. In this case, a simple model indicates that about 1/3 of the galaxy's HI was stripped during a time interval of <1 Gyr. Alternatively, the tail may be the remnant of an interaction between HCG 44 and NGC 3162, a spiral galaxy now ~650 kpc away from the group. Regardless of the precise formation mechanism, the detected HI tail shows for the first time direct evidence of gas stripping in HCG 44. It also highlights that deep HI observations over a large field are needed to gather a complete census of this kind of events in the local Universe.
    Monthly Notices of the Royal Astronomical Society 09/2012; 428(1). DOI:10.1093/mnras/sts033 · 5.23 Impact Factor
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    ABSTRACT: The Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) is a high impact scientific program which will see its final official release open to the world in 2012. That release will seal the legacy aspect of the survey which has already produced a large collection of scientific articles with topics ranging from cosmology to the Solar system. The survey core science was focused on dark energy and dark matter: the full realization of the scientific potential of the data set gathered between 2003 and 2009 with the MegaCam wide-field imager mounted at the CFHT prime focus is almost complete with the Supernovae Legacy Survey (SNLS) team preparing its third and last release (SNLS5), and the CFHTLenS team planning the release based around the cosmic shear survey later this year. While the data processing center TERAPIX offered to the CFHTLS scientific community regular releases over the course of the survey in its data acquisition phase (T0001-T0006), the final release took three years to refine in order to produce a pristine data collection photometrically calibrated at better than the percent both internally and externally over the total survey surface of 155 square degrees in all five photometric bands (u*, g’, r’, i’, z’). This final release, called T0007, benefits from the various advances in photometric calibration MegaCam has benefited through the joint effort between SNLS and CFHT to calibrate MegaCam at levels unexplored for an optical wide-field imager. T0007 stacks and catalogs produced by TERAPIX will be made available to the world at CADC while the CDS will offer a full integration of the release in its VO tools from VizieR to Aladin. The photometric redshifts have been produced to be released in phase with the survey. This proceeding is a general introduction to the survey and aims at presenting its final release in broad terms.
    Proceedings of SPIE - The International Society for Optical Engineering 09/2012; DOI:10.1117/12.925584 · 0.20 Impact Factor

Publication Stats

761 Citations
224.67 Total Impact Points

Institutions

  • 2014
    • Shanghai Jiao Tong University
      Shanghai, Shanghai Shi, China
  • 2012
    • University of California, Irvine
      • Department of Physics and Astronomy
      Irvine, California, United States
  • 2001–2003
    • Observatoire de Paris
      Lutetia Parisorum, Île-de-France, France