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 ACS Virgo and Fornax Cluster Surveys
Program Galaxies
Mosaic showing the 100 ACS Virgo Cluster Survey galaxies, sorted by their apparent B-band magnitude. Galaxy luminosity decreases from left to right, and from top to bottom. Nearly all of these galaxies fall along the red sequence of the Virgo Cluster.
A Survey of Early-Type (Red Sequence) Galaxies in the Virgo and Fornax Clusters
Astronomers divide galaxies into two broad categories based on their location in the colour-magnitude diagram (CMD) where galaxies separate into two distinct populations: (1) a “Red Sequence” of old, gas-poor, mostly passively evolving galaxies; and (2) a “Blue Cloud” of younger, gas-rich galaxies that are continuing to form stars.
(Left) Schematic representation of the galaxy colour-magnitude diagram (CMD) showing two populations. (Right) Location in the CMD of galaxies from the ACS Virgo and Fornax Cluster Surveys (blue and red symbols, respectively). The grey scale image is from Baldry et al. (2006) and is based on observations of thousands of low-redshift galaxies from the Sloan Digital Sky Survey. Figure adapted from Côté et al. (2009).
In fact, these two populations were first characterized in 1970s by astronomers studying “early-type” and “late-type” galaxies in the Virgo Cluster. These respective morphological classifications correspond broadly with the Red Sequence (E, S0, and their “dwarf” varieties) and Blue Cloud populations (Sa-Irr) seen in CMDs.
(Left) Early-type (E + S0 + dE + dS0 + dE,N + dS0,N) luminosity function for galaxies belonging to the Virgo Cluster from Sandage et al. (1985). The solid curve is the best-fit Schechter Function. (Right) The luminosity function of early-type galaxies in Virgo (dashed histogram and open symbols) compared to that of the ACS Virgo Cluster Survey program galaxies (filled histogram and symbols). From Côté et al. (2004, ACS Virgo Cluster Survey Paper I).
The ACSVCS and ACSFCS Surveys targeted an unbiased sample of 143 early-type (red sequence) galaxies in the Virgo and Fornax clusters. The sample was chosen without any further selection on the basis of morphology, given the well-known ambiguities involved in quantitatively distinguishing E galaxies from S0s, and “giants” from “dwarfs”. The final selection criteria for the two surveys were the following:
ACS Virgo Cluster Survey (100 galaxies):
− Morphological Types: E, S0, E/S0, S0/E, dE, dS0, dE,N, dS0,N
− B-band magnitudes: 9.31 to 15.97 mag
ACS Fornax Cluster Survey (43 galaxies):
− Morphological Types: E, S0, E/S0, S0/E, dE, dS0, dE,N, dS0,N
− B-band magnitudes: 9.4 to 15.5 mag
The ACSVCS sample is 100% complete for Virgo early-types down to B ≈ 12.15 (MB ≈ −19.0) and 61% complete overall for early-types brighter than B ≈ 16.0 (MB ≈ −15.2). By contrast, the ACSFCS sample is 100% complete for early-types in Fornax down to its limiting magnitude of B ≈ 15.5 (MB ≈ −16.0)
For more details on the sample galaxies, including adopted and measured properties, please consult the individual publications from the surveys.