Chengze Liu

Galaxies at the Extremes: Ultra-diffuse Galaxies in the Virgo Cluster

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 are comparable in size but lower in surface brightness than the large ultradiffuse LSB galaxies recently identified in the Coma cluster, and are located well within Virgos 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.

Stripped gas as fuel for newly formed H ii regions in the encounter between VCC 1249 and M 49: a unified picture from NGVS and GUViCS

Context. We study the peculiar interacting galaxy system of VCC 1249/M 49 located in the core of the Virgo B subcluster. Owing to a recent interaction between the dwarf galaxy VCC 1249 and the halo gas of the elliptical galaxy M 49, neutral hydrogen has been displaced from the interstellar medium of this dwarf into the Virgo intracluster medium. Observations also reveal multiple compact star-forming regions (aka H  II regions) that are embedded in this H  I cloud, with a projected separation up to 13 kpc from VCC 1249 in the northwest direction. Aims. Motivated by recent near-ultraviolet imaging from the GALEX Ultraviolet Virgo Cluster Survey (GUViCS) of the VCC 1249/M 49 system that shows significant ongoing/recent star formation in the compact regions, we aim to constrain the origin of these outlying H  II regions with a multi-wavelength approach. Methods. Using deep optical (u,g,i,z) imaging from the Next Generation Virgo Cluster Survey (NGVS) and new Hα imaging obtained at the San Pedro Martir observatory together with Keck long-slit spectroscopy, we characterize the star formation rates, ages, and metallicity of VCC 1249 and its outlying compact regions. Moreover, we analyze the color and luminosity profile of the galaxy to investigate its recent interaction with M 49. Results. Our new observations indicate that VCC 1249 underwent a recent interaction with M 49 in which both ram-pressure stripping and tidal interaction occured. The joint action of the two mechanisms led to the removal of the H  I gas from the interstellar medium of VCC 1249, while the gravitational tides triggered the stellar tail and counter-tail of VCC 1249. Our stellar population synthesis analysis reveals that the star formation in this galaxy was truncated around 200 Myr ago and that the outlying H  II regions were born in situ ≈10 Myr ago out of pre-enriched gas removed from the dwarf galaxy. These observations also reveal that interactions between central and satellite galaxies similar to those between VCC 1249/M 49 may be an effective way of dispersing metals into the halos of massive galaxies.

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 similar to 16 deg(2) covering the region between M49 and M87. We present observations of the central 4 deg(2) centered on Virgos 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 5s 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 mu(Ks) similar or equal to 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 Virgos 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 NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). XIII. THE LUMINOSITY AND MASS FUNCTION OF GALAXIES IN THE CORE OF THE VIRGO CLUSTER AND THE CONTRIBUTION FROM DISRUPTED SATELLITES

We present measurements of the galaxy luminosity and stellar mass function in a 3.71 deg

THE NEXT GENERATION VIRGO CLUSTER SURVEY. X. PROPERTIES OF ULTRA-COMPACT DWARFS IN THE M87, M49, AND M60 REGIONS

^2

THE NEXT GENERATION VIRGO CLUSTER SURVEY. XV. THE PHOTOMETRIC REDSHIFT ESTIMATION FOR BACKGROUND SOURCES

(0.3 Mpc

ELUCID - Exploring the Local Universe with reConstructed Initial Density field III: Constrained Simulation in the SDSS Volume

^2

The GALEX Ultraviolet Virgo Cluster Survey (GUViCS) - III. The ultraviolet source catalogs

) area in the core of the Virgo cluster, based on

EXPLORING THE COSMIC REIONIZATION EPOCH IN FREQUENCY SPACE: AN IMPROVED APPROACH TO REMOVE THE FOREGROUND IN 21 cm TOMOGRAPHY

ugriz

THE NEXT GENERATION VIRGO CLUSTER SURVEY XVI: THE ANGULAR MOMENTUM OF DWARF EARLY-TYPE GALAXIES FROM GLOBULAR CLUSTER SATELLITES

data from the Next Generation Virgo Cluster Survey (NGVS). The galaxy sample consists of 352 objects brighter than