The ACS Virgo and Fornax Cluster Surveys were unprecedented surveys of early-type galaxies belonging to two benchmark clusters in the local universe, Virgo and Fornax. The surveys were based on ACS imaging from the Hubble Space Telescope (HST), and helped change the way astronomers think about galaxy formation.
Left: An intermediate-luminosity galaxy (VCC1431) in the Virgo Cluster observed with the Advanced Camera for Surveys (ACS) on HST as part of the ACS Virgo Cluster Survey, which targeted 100 early-type galaxies (Cote et al. 2004). Note the central nucleus or “luminosity excess” (see below). A similar survey of the Fornax Cluster, targeting 43 galaxies, is described in Jordan et al. (2007). Top: The ACS/WFC CCDs before the camera was assembled.
The ACS Virgo and Fornax Cluster Surveys were unprecedented surveys of early-type galaxies belonging to two benchmark clusters in the local universe, Virgo and Fornax. The surveys were based on ACS imaging from the Hubble Space Telescope (HST), and helped change the way astronomers think about galaxy formation.
The ACS Virgo and Fornax Cluster Surveys were unprecedented surveys of early-type galaxies belonging to two benchmark clusters in the local universe, Virgo and Fornax. The surveys were based on ACS imaging from the Hubble Space Telescope (HST), and helped change the way astronomers think about galaxy formation.
The ACS Virgo and Fornax cluster surveys produced more than two dozen publications on topics ranging from the core and global structure of early-type galaxies, to globular cluster systems, new families of hot stellar systems (such as “Ultra Compact Dwarf Galaxies” and “Faint Fuzzies”) and the extragalactic distance scale. Some scientific highlights and data products from the surveys include:
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The first simultaneous characterization of the central and global structure for a large sample of early-type galaxies in the nearby universe (Virgo), made possible by the large field of view of the ACS instrument on HST (Ferrarese et al. 2006a; Cote et al. 2006; Cote et al. 2007).
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The demonstration that the Sersic family of models provides a remarkably accurate description of the brightness profiles of early-type galaxies spanning nearly three orders of magnitude in luminosity (i.e., from “giant” to “dwarf” galaxies, Ferrarese et al. 2006a). These findings build upon pioneering studies by Caon et al. (1993), Graham et al. (2003), Graham & Guzman (2003) and Jerjen & Binggeli (1997).
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The finding of a systematic transition from a central luminosity “deficit” to “excess” in the central regions of galaxies, relative to the global Sersic model fit, and a dramatic upward revision of the frequency of distinct nuclear components in the centers of low- and intermediate-luminosity galaxies (Ferrarese et al. 2006a; Cote et al. 2006; Cote et al. 2007). Once again, see the series of earlier papers by Graham and collaborators, including Graham et al. (2003), Graham & Guzman (2003) and Trujillo et al. (2004), as well as Carolla et al. (1998), Boker et al. (2002, 2004), Lotz et al. (2004) and Grant et al. (2005).
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The realization that these central excesses/nuclei probably arise, for at least some galaxies, through gas inflows and starbursts expected in mergers and accretions, as had been predicted by numerical models (Cote et al. 2006, Cote et al. 2007). See also Mihos & Hernquist (1994), who anticipated these results using pioneering numerical simulations.
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The discovery that the light “excesses” (i.e., compact stellar nuclei) in the faintest galaxies contain roughly the same percentage of the total galaxy mass as do the Supermassive Black Holes (SBHs) in the brightest galaxies, suggesting a possible link between these two components (Ferrarese et al. 2006b, Cote et al. 2006). See the contemporaneous papers by Rossa et al. (2006) and Wehner and Harris (2006), and the comprehensive subsequent study by Seth et al. (2008).
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A demonstration that the early-type galaxy populations do not show a dramatic “dichotomy” in terms of their central brightness profile slopes, as was previously believed; the ACS Virgo Cluster Survey was the first study to show that the previously reported class of “power-law galaxies” actually have a two-component structure on small scales (Ferrarese et al. 2006a; Cote et al. 2007). Once again, see also Jerjen & Binggeli (1997), Graham & Guzman (2003), as well as Rest et al. (2001) and Ravindranath et al. (2001).
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A large and homogeneous catalog of more than ≈ 10,000 globular cluster candidates in early-type galaxies (Jordan et al. 2009).
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The demonstration that the fundamental properties of globular cluster systems show unexpected continuous trends with host galaxy luminosity. Specific examples include their luminosity functions, size distributions, color/metallicity distributions, and formation efficiencies (Jordan et al.2005, 2006, 2007; Peng et al. 2006a,b, 2008; Mieske et al. 2006, 2010; Sivakoff et al. 2007; Masters et al. 2010; Villegas et al. 2010). These results build upon a number of previous studies by other researchers, including Gebhardt & Kissler-Patig (1998), Larsen et al. (2001) and Kundu et al. (2001).
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The discovery of Ultra-Compact Dwarf (UCD) galaxies in the Virgo Cluster, the first measurements for the dynamical masses of these systems, and the discovery of an apparently fundamental transition between globular clusters and UCDs at ≈ 2-3 million solar masses (Hasegan et al. 2005).
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The measurement of accurate SBF distances (i.e., typical errors of ≈ 0.5 Mpc) for a large sample of galaxies in both the Virgo and Fornax Clusters, the direct measurement of the line-of-sight depth of Virgo and a precise measurement of the relative distance of the two clusters (Mei et al. 2005a,b, 2007; Blakeslee et al. 2009).
Please see the science highlights to learn more about these and other topics. To read or download individual papers, see the publications section.
The Survey Teams
The Survey Teams
The ACS Virgo and Fornax Cluster Surveys were unprecedented surveys of early-type galaxies belonging to two benchmark clusters in the local universe, Virgo and Fornax. The surveys were based on ACS imaging from the Hubble Space Telescope (HST), and helped change the way astronomers think about galaxy formation.
Program Galaxies
Left: An intermediate-luminosity galaxy (VCC1431) in the Virgo Cluster observed with the Advanced Camera for Surveys (ACS) on HST as part of the ACS Virgo Cluster Survey, which targeted 100 early-type galaxies (Cote et al. 2004). Note the central nucleus or “luminosity excess” (see below). A similar survey of the Fornax Cluster, targeting 43 galaxies, is described in Jordan et al. (2007). Top: The ACS/WFC CCDs before the camera was assembled.
The Virgo Cluster is the rich cluster nearest to the Milky Way, and the dominant mass concentration in the local universe. It also represents the nearest large collection of early-type (red sequence) galaxies within ~50 Mpc. At a distance of ≈16.5 Mpc, it has historically played a central role in furthering our understanding of galaxy evolution, supermassive black holes, the extragalactic distance scale, the intracluster medium, extragalactic star clusters, and countless other topics in modern astrophysics.
The Virgo Cluster is the rich cluster nearest to the Milky Way, and the dominant mass concentration in the local universe. It also represents the nearest large collection of early-type (red sequence) galaxies within ~50 Mpc. At a distance of ≈16.5 Mpc, it has historically played a central role in furthering our understanding of galaxy evolution, supermassive black holes, the extragalactic distance scale, the intracluster medium, extragalactic star clusters, and countless other topics in modern astrophysics.
The Fornax Cluster is smaller and more compact than Virgo. At a slightly larger distance of ≈20.0 Mpc, it offers an unique opportunity to study the fossil record of galaxy formation in rather different environment than the Virgo Cluster.
The Next Generation Virgo Cluster Survey (NGVS)
Science Highlights
The NGVS has produced nearly 50 publications by the survey team, most focusing on the Virgo cluster and its member galaxies, but also ranging from the outer solar system to the high-redshift clusters. In addition, given the high legacy value of the survey, NGVS data have been used in numerous other publications. Here we describe some of the key scientific highlights by the survey team.
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The development of a new observing strategy for MegaCam, "Elixir LSB", optimized for the characterization of extended and/or low surface brightness features based on a limited number of images per field (Ferrarese et al. 2012, ApJS, 200, 4).
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The discovery of an extremely remote member of the Oort Cloud, 2010 GB_174, with a perihelion distance of 48.5 AU and one of only a handful of objects with a semi-major axis greater than 300 AU (Chen et al. 2013, ApJ, 775, L8).
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The introduction of a powerful new source classification and diagnostic tool, the uiK colour-colour diagram, to be used for the efficient selection of foreground stars, background galaxies and globular clusters from broadband optical and IR photometry (Munoz et al. 2014, ApJS, 210, 4).
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A tomographic analysis of the Sagitarrius Stream, including the detection of a clear distance gradient (from 25 to 40 kpc across the NGVS field) based on main-sequence turnoff halo stars which are detected reliably out to distances of ~ 90 kpc (Lokhorst et al. 2016, ApJ, 819, 124).
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The systematic detection and characterization of dozens of ultra-diffuse galaxies (UDGs) in the Virgo Cluster, including their structural, morphological and dynamical properties, based on deep, homogeneous NGVS imaging (Mihos 2015, ApJ, 809, 21; Toloba et al. 2018, ApJ, 856, 31; Lim et al. 2020, ApJ, 899, 69).
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State-of-the-art measurements of the luminosity function, colour-magnitude relation and intrinsic shape distributions based on hundreds of galaxies detected in the core of the Virgo Cluster, spanning a factor of roughly one million in luminosity: i.e., from super-giant elliptical to ultra-faint dwarf scales (Sanchez-Janssen et al. 2016, ApJ, 820, 69; Roediger et al. 2017, ApJ, 836, 120; Ferrarese et al. 2020, ApJ, 890, 126).
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A comprehensive analysis of galactic nuclei from NGVS imaging and space-based imaging and spectroscopy including the characterization of their occupation and mass fractions as a function of host luminosity, intrinsic shape and environment (Spengler et al. 2017, ApJ, 849, 55; Sanchez-Janssen et al. 2019a, ApJ, 878, 18; Sanchez-Janssen et al. 2019b, MNRAS, 486, L1).
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A census of ultra-compact dwarf galaxies (UCDs) in the Virgo cluster, including a catalogue of hundreds of UCD candidates, the discovery of the most massive UCD in the nearby universe, and the discovery of a correlation between location in the cluster and the prominence of the diffuse envelopes surrounding nucleated dwarf galaxies and some UCDs: strong evidence that at least some UCDs form through tidal stripping of low- and intermediate-mass galaxies (Liu et al. 2015a, ApJ, 812, 34; Liu et al. 2015b, ApJ, 812, L2; Liu et al. 2020, ApJS, 250, 17).
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Photometric redshift measurements for more than 1.2 million galaxies within the NGVS field, as well as shape measurements, made during conditions of excellent seeing. Both sets of measurements were analyzed, in the context of four other weak lensing surveys, to constrain the ellipticity of galaxy-scale dark matter haloes (Raichoor et al. 2014, ApJ, 797, 107; Schrabback et al. 2021, A&A, in press).
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The discovery of nearly 300 RR Lyrae variables belonging to the Galactic halo, including some of the most distant stars known in the Milky Way, with distances larger than 300 kpc. These stars show an 1/r^3.5 power-law radial density profile over most of this distance range with no signs of a break out to the viral radius of the Milky Way (Feng et al. 2021, ApJ, submitted).
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The measurement of accurate surface brightness fluctuation distances (i.e., typical errors of ≈ 1.0 Mpc) for a large number of Virgo cluster members, and a new measurement of the cluster's line-of-sight depth (2.4 +/- 0.4 Mpc; Cantiello 2018, ApJ, 856, 126; Cantiello et al. 2021, in preparation).