The WiggleZ Dark Energy Survey: Survey Design and First Data Release

TL;DR

The WiggleZ study tackles the problem of constraining dark energy by measuring baryon acoustic oscillations at intermediate redshifts. It combines GALEX UV selection with optical data to target emission-line galaxies in $0.2<z<1.0$, assembling a ~1,000 deg^2 survey designed to map a volume of ~1 Gpc^3 and achieve BAO precision around a few percent. Through an extensive spectroscopic campaign with the AAOmega/2dF system, the project demonstrates robust redshift measurements from strong emission lines, a high fraction of high-z targets after optical color cuts, and a public data release (DR1) containing 169,000 spectra and 100,138 redshifts at half-way. The initial results reveal strong small-scale clustering, predominantly star-forming blue galaxies often in interacting systems, and a well-structured data platform enabling broad community access, setting the stage for precise BAO and dark-energy constraints from WiggleZ.

Abstract

The WiggleZ Dark Energy Survey is a survey of 240,000 emission line galaxies in the distant universe, measured with the AAOmega spectrograph on the 3.9-m Anglo-Australian Telescope (AAT). The target galaxies are selected using ultraviolet photometry from the GALEX satellite, with a flux limit of NUV<22.8 mag. The redshift range containing 90% of the galaxies is 0.2<z<1.0. The primary aim of the survey is to precisely measure the scale of baryon acoustic oscillations (BAO) imprinted on the spatial distribution of these galaxies at look-back times of 4-8 Gyrs. Detailed forecasts indicate the survey will measure the BAO scale to better than 2% and the tangential and radial acoustic wave scales to approximately 3% and 5%, respectively. This paper provides a detailed description of the survey and its design, as well as the spectroscopic observations, data reduction, and redshift measurement techniques employed. It also presents an analysis of the properties of the target galaxies, including emission line diagnostics which show that they are mostly extreme starburst galaxies, and Hubble Space Telescope images, which show they contain a high fraction of interacting or distorted systems. In conjunction with this paper, we make a public data release of data for the first 100,000 galaxies measured for the project.

Figures (22)

• Figure 1: The sky distribution of the seven WiggleZ survey regions compared to the coverage of the SDSS, RCS2 and GALEX data sets at the end of 2008.
• Figure 2: Properties of GALEX data used to select WiggleZ targets. Upper panel: distribution of exposure times. Lower panel: distribution of average dust extinction of each tile.
• Figure 3: Distribution of dust in each of the survey fields. The grey scale shows the Schlegel98 extinction values such that white is $E(B-V)=0.02$ and black is $E(B-V)=0.1$. The horizontal and vertical axes in each panel denote the Right Ascension and Declination, respectively, measured in degrees.
• Figure 4: Number counts of GALEX NUV detections in tiles from the 15-hour region as a function of dust extinction. The NUV magnitude limit of the WiggleZ survey is indicated by a vertical dashed line in each plot. In the left hand panels (a, b) we plot all objects detected before and after the dust correction. The counts are binned by the average dust extinction in each tile, one curve for each bin (see key). The upper panel shows the raw counts; in the lower panel the dust correction has been applied to every individual object. The improved agreement of the power-law region of the number counts in panel b demonstrates the effectiveness of the dust correction. The right hand panels (c, d) are similar, but only count objects that satisfy the WiggleZ target selection criteria. Panel d shows that the target numbers at the NUV survey limit are more sensitive to dust than the total counts of detections shown in panel b.
• Figure 5: The basic WiggleZ target selection criteria. The rectangle marked by the dashed line denotes the region in FUV-NUV,NUV-r colour space where WiggleZ targets lie. The solid lines are the model tracks for seven galaxy templates as a function of redshift for $z > 0.5$. The first track, from left to right, is for a Lyman break galaxy template Steidel1996. The remaining tracks are two starburst templates Kinney1996 and a series of (Im to E/S0) local galaxy templates Coleman1980, all extended in wavelength range by matching them with Bruzual1993 models (Hsaio-Wen Chen, private communication). The dashed lines at the end of the solid lines are these models for $z \le 0.5$. Also shown as points are galaxies from deep GALEX imaging that were detected in all three bands and have published redshifts from the DEEP2 survey Davis2003. The triangles indicate objects with redshift $z > 0.5$.