Unlike most other sciences, astrophysics is driven both by experimentation and observation. It is the role of surveys to discover, catalog and study astrophysical systems, and surveys have traditionally played an indispensable role in advancing the discipline. Surveys that are both complete and unbiased are especially powerful resources since they are the best tools for discovering new and unexpected phenomena, and for understanding the fundamental physics that underlies the formation of astronomical objects of all kinds.

Thanks to MegaPrime’s square degree field of view, and the exceptional natural seeing on Mauna Kea, CFHT is arguably the world’s premier facility for wide-field imaging surveys. The NGVS is designed fully exploit this unique capability, and is poised to become one of CFHT’s most valuable legacies.

Virgo SCIENCe

By imaging the 104 deg2 region enclosed within the virial radius of the Virgo cluster, in all five SDSS filters (u*,g′,r′,i′ ,z′), the Next Generation Virgo Cluster Survey (NGVS) will provide an unprecedented view of baryonic substructures spanning a factor 107 in mass, from supra-L* giants to small spheroidal galaxies, tidal debris and globular star clusters, and serve as a much needed local reference point for observational tests of cosmological models.

With a point-source depth of g′ ∼25.7 mag (10σ) and a corresponding surface brightness limit of μ(g′) ∼27.7 mag arcsec-2 (2σ), the NGVS will completely supersede all previous optical studies of this uniquely important system. By leveraging the vast amount of data available at other wavelengths, it will allow us to address a wide range of fundamental astrophysical questions, including:

1. •The faint-end shape of the luminosity function
   

2. •The characterization of galaxy scaling relations over a factor 107 in mass
   

3. •The study of stellar nuclei and their connection to supermassive black holes
   

4. •The connection between cluster, galaxies and the intracluster medium
   

5. •The fossil record of star formation and chemical enrichment in dense environments.
   

Foreground SCIENCe

The true power of surveys lies in their legacy value and in their ability to enable a diverse array of science investigations. True to the spirit of surveys, the NGVS legacy will extend far beyond the study of the Virgo cluster.

The NGVS field is located in the direction of the “Virgo overdensity”, the largest clump of tidal debris ever detected in the outer halo of the Milky Way. By combining the NGVS data with other surveys of the Galactic halo,  it will be possible to compare the line-of-sight distribution of stars along different halo sightlines with Galactic halo models, and to measure directly the shape and symmetry of the stellar halo.

Furthermore, at an ecliptic latitude of β=14°, the NGVS is well suited to the study of the outer solar system. It is expected that ∼90 Kuiper Belt Objects (KBOs) will leave a detectable trail in the NGVS fields. Dedicated follow-up observations to secure the KBO orbits have the potential of advancing our understanding of planetary formation.

Background SCIENCe

The NGVS will have the deepest and widest contiguous coverage of any optical medium-deep survey to date. At a Galactic latitude of b=75°, the NGVS fields are relatively unaffected by Galactic extinction and contamination from foreground stars, and are naturally conducive to studies of background structures. In particular, the NGVS will make it possible to:

1. •Discover ≈2000 galaxy clusters at redshifts between 0.1 and 1.0, and enable weak lensing measurements out to z ≈ 0.5.
   

2. •Discover up to 300 strong lensing structures, spanning the full range from massive galaxies to rich clusters.
   

3. •Enable a high-quality measurements of the matter power spectrum on scales beyond 8° through cosmic shear studies.
   

A comparison between the NGVS and a number of prominent deep and wide extragalatic surveys may be found in the table below.

SYNERGISTIC OPPORTUNITIES

The VCC, which serves as standard reference optical survey of the Virgo cluster, is hopelessly out of date by modern standards, and the large number of planned or ongoing surveys of the Virgo Cluster at X-ray, UV, infrared, submm and radio wavelengths (see Table below) are now, ironically, limited by the lack of deep, high quality optical data for this benchmark cluster. The NGVS will represent the perfect complement to surveys of the Virgo cluster at both longer and shorter wavelengths, enabling to address topics such as the properties of the interstellar medium, the history of star formation and chemical enrichment, and the distribution of dark matter.