The VIMOS Public Extragalactic Redshift Survey (VIPERS). An unprecedented view of galaxies and large-scale structure at 0.5<z<1.2

Abstract: We describe the construction and general features of VIPERS, the VIMOS Public Extragalactic Redshift Survey. This `Large Programme' has been using the ESO VLT with the aim of building a spectroscopic sample of ~100,000 galaxies with i_{AB}<22.5 and 0.5<z<1.5. The survey covers a total area of ~24 deg^2 within the CFHTLS-Wide W1 and W4 fields. VIPERS is designed to address a broad range of problems in large-scale structure and galaxy evolution, thanks to a unique combination of volume (~ 5 x 10^7 h^{-3} Mpc^3) and sampling rate (~ 40%), comparable to state-of-the-art surveys of the local Universe, together with extensive multi-band optical and near-infrared photometry. Here we present the survey design, the selection of the source catalogue and the development of the spectroscopic observations. We discuss in detail the overall selection function that results from the combination of the different constituents of the project. This includes the masks arising from the parent photometric sample and the spectroscopic instrumental footprint, together with the weights needed to account for the sampling and the success rates of the observations. Using the catalogue of 53,608 galaxy redshifts composing the forthcoming VIPERS Public Data Release 1 (PDR-1), we provide a first assessment of the quality of the spectroscopic data. Benefiting from the combination of size and detailed sampling of this dataset, we conclude by presenting a map showing in unprecedented detail the large-scale distribution of galaxies between 5 and 8 billion years ago. [abridged]

• The paper presents VIPERS, a survey that gathered redshifts for about 100,000 galaxies to map cosmic structure at 0.5<z<1.2.
• It employs a precise color-color selection method achieving over 98% completeness for z>0.6 and a target sampling rate near 40%.
• The study attains a redshift precision of σz/(1+z) = 4.7×10⁻⁴, offering critical insights into galaxy clustering and dark energy.

Analysis of the VIMOS Public Extragalactic Redshift Survey (VIPERS)

The VIMOS Public Extragalactic Redshift Survey (VIPERS) constitutes a crucial advancement in the study of large-scale structure and galaxy evolution across the redshift range $0.5 < z < 1.2$. This survey utilizes the ESO VLT with the VIMOS spectrograph. VIPERS aims to assemble a spectroscopic sample of approximately 100,000 galaxies with magnitudes $i_{AB}<22.5$, which is significant for understanding galaxy distribution and clustering over a substantial cosmological volume of approximately $5 \times 10^7 \, h^{-3}\mathrm{Mpc}^3$.

The survey adopts several strategies to achieve its scientific goals. The observational data extends over a sky area of about 24 square degrees within the CFHTLS-Wide fields, providing a unique combination of volume and sampling density analogous to local Universe surveys. This design allows VIPERS to deliver unprecedented insights into the large-scale structures present during an epoch when the Universe was approximately half its present age.

Key Methodological Features

The survey employs a color selection technique utilizing data from the CFHTLS to isolate galaxies likely to reside at $z > 0.5$. This allows an efficient allocation of spectroscopic resources by minimizing the inclusion of low-redshift foreground objects. The color-color selection is demonstrated to maintain $>98\%$ completeness for $z > 0.6$, verified against pre-existing datasets from VVDS, highlighting the robustness of this approach.

VIPERS achieved a high target sampling rate (TSR) of approximately 40% due to the optimal placement of VIMOS slits, and a similarly high spectroscopic success rate (SSR). These efficiencies are important, given the necessity of balancing observing conditions and instrument constraints with scientific sampling goals.

Additionally, redshift accuracy is a critical aspect of VIPERS, addressed through careful validation processes resulting in a standard redshift error of $\sigma_z/(1+z) = 4.7 \times 10^{-4}$. This precision enables detailed statistical analyses of structure growth over the redshift range probed.

Scientific Implications

Quantifying large-scale structure, the survey explores galaxy clustering, contributing significantly to our understanding of galaxy bias and dark matter halo occupation. Beyond providing a detailed map of the cosmic web at a crucial epoch, VIPERS enhances insights into the underlying cosmological model, particularly in relation to the nature of dark energy and possible deviations from General Relativity on large scales.

The impact extends to studies of galaxy evolution. VIPERS' rich dataset informs on the stellar mass, star formation rates, and other properties of galaxies, thereby elucidating how these evolve in relation to their environment. The magnitude of this dataset allows for high-confidence measurements of key relationships, such as the color-density relation, which is pivotal in characterizing how galaxies evolve within varying density environments.

Future Prospects

The insights gained from VIPERS will propel subsequent investigations in cosmology and galaxy evolution. The VIPERS data, especially when integrated with complementary data such as weak lensing maps, can serve as critical inputs into models of galaxy formation and the broader framework of structure formation. Furthermore, subsequent data releases can be anticipated to expand the breadth of research, inviting broader community participation and enabling discoveries well beyond the original scope envisaged by the VIPERS Team.

VIPERS, through strategic design and thorough data utilization, not only offers a definitive snapshot of large-scale cosmic structure at an intermediate epoch but also sets a benchmark for future extragalactic surveys. As a public dataset, it promises a continued scientific yield, fostering advancements in astrophysics and cosmology.