Globular Clusters as Tracers of Fine Structure in the Dramatic Shell Galaxy NGC 474

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Virgo Redux: The Masses and Stellar Content of Nuclei in Early-type Galaxies from Multiband Photometry and Spectroscopy

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Erratum: “Virgo Redux: The Masses and Stellar Content of Nuclei in Early-type Galaxies from Multiband Photometry and Spectroscopy” (2017, ApJ, 849, 55)

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THE NEXT GENERATION VIRGO CLUSTER SURVEY. XXII. SHELL FEATURE EARLY-TYPE DWARF GALAXIES IN THE VIRGO CLUSTER

International audienceThe Next Generation Virgo Cluster Survey is a deep (with a 2sigma detection limit mug = 29 mag arcsec-2 in the g-band) optical panchromatic survey targeting the Virgo cluster from its core to virial radius, for a total areal coverage of 104 square degrees. As such, the survey is well suited for the study of galaxies' outskirts, haloes, and low surface brightness features that arise from dynamical interactions within the cluster environment. We report the discovery of extremely faint (mug > 25 mag arcsec-2) shells in three Virgo cluster early-type dwarf galaxies: VCC 1361, VCC 1447, and VCC 1668. Among them, VCC 1447 has an absolute magnitude Mg = -11.71 mag and is the least massive galaxy with a shell system discovered to date. We present a detailed study of these low surface brightness features. We detect between three and four shells in each of our galaxies. Within the uncertainties, we find no evidence of a color difference between the galaxy main body and shell features. The observed arcs of the shells are located up to several effective radii of the galaxies. We further explore the origin of these low surface brightness features with the help of idealized numerical simulations. We find that a near equal mass merger is best able to reproduce the main properties of the shells, including their quite symmetric appearance and their alignment along the major axis of the galaxy. The simulations provide support for a formation scenario in which a recent merger, between two near-equal mass, gas-free dwarf galaxies, forms the observed shell systems

The Next Generation Virgo Cluster Survey (NGVS). XXVI. The Issues of Photometric Age and Metallicity Estimates for Globular Clusters

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Dwarfs or Giants? Stellar Metallicities and Distances from ugrizG Multiband Photometry

International audienceWe present a new fully data-driven algorithm that uses photometric data from the Canada-France-Imaging-Survey (CFIS; u), Pan-STARRS 1 (PS1; griz), and Gaia (G) to discriminate between dwarf and giant stars and to estimate their distances and metallicities. The algorithm is trained and tested using the SDSS/SEGUE spectroscopic dataset and Gaia photometric/astrometric dataset. At [Fe/H]< −1.2, the algorithm succeeds in identifying more than 70% of the giants in the training/test set, with a dwarf contamination fraction below 30% (with respect to the SDSS/SEGUE dataset). The photometric metallicity estimates have uncertainties better than 0.2 dex when compared with the spectroscopic measurements. The distances estimated by the algorithm are valid out to a distance of at least ∼ 80 kpc without requiring any prior on the stellar distribution, and have fully independent uncertainities that take into account both random and systematic errors. These advances allow us to estimate these stellar parameters for approximately 12 million stars in the photometric dataset. This will enable studies involving the chemical mapping of the distant outer disc and the stellar halo, including their kinematics using the Gaia proper motions. This type of algorithm can be applied in the Southern hemisphere to the first release of LSST data, thus providing an almost complete view of the external components of our Galaxy out to at least ∼ 80 kpc. Critical to the success of these efforts will be ensuring well-defined spectroscopic training sets that sample a broad range of stellar parameters with minimal biases. A catalogue containing the training/test set and all relevant parameters within the public footprint of CFIS is available online

Erratum: “The Next Generation Virgo Cluster Survey. X. Properties of Ultra-compact Dwarfs in the M87, M49, and M60 Regions” (2015, APJ, 812, 34)

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Newly discovered dwarf galaxies in the MATLAS low density fields

International audienceWe present the photometric properties of 2210 newly identified dwarf galaxy candidates in the MATLAS fields. The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) deep imaging survey mapped ˜142 deg2 of the sky around nearby isolated early type galaxies using MegaCam on the Canada-France-Hawaii Telescope, reaching surface brightnesses of ˜ 28.5 - 29 in the g-band. The dwarf candidates were identified through a direct visual inspection of the images and by visually cleaning a sample selected using a partially automated approach, and were morphologically classified at the time of identification. Approximately 75% of our candidates are dEs, indicating that a large number of early type dwarfs also populate low density environments, and 23.2% are nucleated. Distances were determined for 13.5% of our sample using pre-existing zspec measurements and HI detections. We confirm the dwarf nature for 99% of this sub-sample based on a magnitude cut Mg = -18. Additionally, most of these (˜90%) have relative velocities suggesting that they form a satellite population around nearby massive galaxies rather than an isolated field sample. Assuming that the candidates over the whole survey are satellites of the nearby galaxies, we demonstrate that the MATLAS dwarfs follow the same scaling relations as dwarfs in the Local Group as well as the Virgo and Fornax clusters. We also find that the nucleated fraction increases with Mg, and find evidence of a morphology-density relation for dwarfs around isolated massive galaxies