Scott M. Croom

The WiggleZ Dark Energy Survey: mapping the distance–redshift relation with baryon acoustic oscillations

We present measurements of the baryon acoustic peak at redshifts z = 0.44, 0.6 and 0.73 in the galaxy correlation function of the final dataset of the WiggleZ Dark Energy Survey. We combine our correlation function with lower-redshift measurements from the 6-degree Field Galaxy Survey and Sloan Digital Sky Survey, producing a stacked survey correlation function in which the statistical significance of the detection of the baryon acoustic peak is 4.9-σ relative to a zero-baryon model with no peak. We fit cosmological models to this combined baryon acoustic oscillation (BAO) dataset comprising six distance-redshift data points, and compare the results to similar fits to the latest compilation of supernovae (SNe) and Cosmic Microwave Background (CMB) data. The BAO and SNe datasets produce consistent measurements of the equation-ofstate w of dark energy, when separately combined with the CMB, providing a powerful check for systematic errors in either of these distance probes. Combining all datasets we determine w = 1.03 ± 0.08 for a flat Universe, consistent with a cosmological constant model. Assuming dark energy is a cosmological constant and varying the spatial curvature, we find k = 0.004± 0.006.

Galaxy and Mass Assembly (GAMA): survey diagnostics and core data release

The Galaxy and Mass Assembly (GAMA) survey has been operating since 2008 February on the 3.9-m Anglo-Australian Telescope using the AAOmega fibre-fed spectrograph facility to acquire spectra with a resolution of R ≈ 1300 for 120 862 Sloan Digital Sky Survey selected galaxies. The target catalogue constitutes three contiguous equatorial regions centred at 9h (G09), 12h (G12) and 14.5h (G15) each of 12 × 4 deg2 to limiting fluxes of rpet < 19.4, rpet < 19.8 and rpet <19.4 mag, respectively (and additional limits at other wavelengths). Spectra and reliable redshifts have been acquired for over 98 per cent of the galaxies within these limits. Here we present the survey footprint, progression, data reduction, redshifting, re-redshifting, an assessment of data quality after 3 yr, additional image analysis products (including ugrizYJHK photometry, S´ersic profiles and photometric redshifts), observing mask and construction of our core survey catalogue (GamaCore). From this we create three science-ready catalogues: GamaCoreDR1 for public release, which includes data acquired during year 1 of operations within specified magnitude limits (2008 February to April); GamaCoreMainSurvey containing all data above our survey limits for use by the GAMA Team and collaborators; and GamaCore-AtlasSV containing year 1, 2 and 3 data matched to Herschel-ATLAS science demonstration data. These catalogues along with the associated spectra, stamps and profiles can be accessed via the GAMA website: http://www.gama-survey.org/

The 6dF Galaxy Survey: final redshift release (DR3) and southern large-scale structures

We report the final redshift release of the 6dF Galaxy Survey (6dFGS), a combined redshift and peculiar velocity survey over the southern sky (|b| > 10°). Its 136 304 spectra have yielded 110 256 new extragalactic redshifts and a new catalogue of 125 071 galaxies making near-complete samples with (K, H, J, r_F, b_J) ≤ (12.65, 12.95, 13.75, 15.60, 16.75). The median redshift of the survey is 0.053. Survey data, including images, spectra, photometry and redshifts, are available through an online data base. We describe changes to the information in the data base since earlier interim data releases. Future releases will include velocity dispersions, distances and peculiar velocities for the brightest early-type galaxies, comprising about 10 per cent of the sample. Here we provide redshift maps of the southern local Universe with z ≤ 0.1, showing nearby large-scale structures in hitherto unseen detail. A number of regions known previously to have a paucity of galaxies are confirmed as significantly underdense regions. The URL of the 6dFGS data base is http://www-wfau.roe.ac.uk/6dFGS.

The 2dF QSO Redshift Survey – XII. The spectroscopic catalogue and luminosity function

We present the final catalogue of the 2dF QSO Redshift Survey (2QZ), based on Anglo-Australian Telescope 2dF spectroscopic observations of 44 576 colour-selected (ub J r) objects with 18.25 < b J < 20.85 selected from automated plate measurement scans of UK Schmidt Telescope (UKST) photographic plates. The 2QZ comprises 23 338 quasi-stellar objects (QSOs), 12 292 galactic stars (including 2071 white dwarfs) and 4558 compact narrow emission-line galaxies. We obtained a reliable spectroscopic identification for 86 per cent of objects observed with 2dF. We also report on the 6dF QSO Redshift Survey (6QZ), based on UKST 6dF observations of 1564 brighter (16 < b J < 18.25) sources selected from the same photographic input catalogue. In total, we identified 322 QSOs spectroscopically in the 6QZ. The completed 2QZ is, by more than a factor of 50, the largest homogeneous QSO catalogue ever constructed at these faint limits (b J < 20.85) and high QSO surface densities (35 QSOs deg -2 ). As such, it represents an important resource in the study of the Universe at moderate-to-high redshifts. As an example of the results possible with the 2QZ, we also present our most recent analysis of the optical QSO luminosity function and its cosmological evolution with redshift. For a flat, Ω m = 0.3 and Ω A = 0.7, universe, we find that a double power law with luminosity evolution that is exponential in look-back time, τ, of the form L* bJ (z) α e 6.15τ , equivalent to an e-folding time of 2 Gyr, provides an acceptable fit to the redshift dependence of the QSO LF over the range 0.4 < z < 2.1 and M bJ < -22.5. Evolution described by a quadratic in redshift is also an acceptable fit, with L* bJ (z) α 10 1.39 z-0.29z 2 .

The 2dF QSO Redshift Survey — I. The optical luminosity function of quasi-stellar objects

We present a determination of the optical QSO luminosity function and its cosmological evolution with redshift for a sample of over 6000 QSOs identified primarily from the first observations of the 2dF QSO Redshift Survey (2QZ). For QSOs with -26<M_B<-23 and 0.35<z<2.3, we find that pure luminosity evolution (PLE) models provide an acceptable fit to the observed redshift dependence of the luminosity function. The luminosity function is best fit by a two-power-law function of the form. Exponential luminosity evolution models, both as a function of look-back time, and as a general second-order polynomial with redshift, were found to provide acceptable fits to the dataset comprising the 2QZ and the Large Bright Quasar Survey. Exponential evolution with look-back time is prefered for q_0=0.05, while the polynomial evolution model is prefered for q_0=0.5. The shape and evolution of the LF at low redshifts (z<0.5) and/or high luminosities, not currently well sampled by the 2dF QSO survey, may show departures from pure luminosity evolution, but the results presented here show that over a significant range of redshift, PLE is a good description of QSO evolution.

The WiggleZ Dark Energy Survey: Joint measurements of the expansion and growth history at z < 1

We perform a joint determination of the distance–redshift relation and cosmic expansion rate at redshifts z = 0.44, 0.6 and 0.73 by combining measurements of the baryon acoustic peak and Alcock–Paczynski distortion from galaxy clustering in the WiggleZ Dark Energy Survey, using a large ensemble of mock catalogues to calculate the covariance between the measurements. We find that D_A(z) = (1205 ± 114, 1380 ± 95, 1534 ± 107) Mpc and H(z) = (82.6 ± 7.8, 87.9 ± 6.1, 97.3 ± 7.0) km s^(−1) Mpc^(−1) at these three redshifts. Further combining our results with other baryon acoustic oscillation and distant supernovae data sets, we use a Monte Carlo Markov Chain technique to determine the evolution of the Hubble parameter H(z) as a stepwise function in nine redshift bins of width Δz = 0.1, also marginalizing over the spatial curvature. Our measurements of H(z), which have precision better than 7 per cent in most redshift bins, are consistent with the expansion history predicted by a cosmological constant dark energy model, in which the expansion rate accelerates at redshift z < 0.7.

Galaxy And Mass Assembly (GAMA): The galaxy stellar mass function at z < 0.06.

We determine the low-redshift field galaxy stellar mass function (GSMF) using an area of 143 deg 2 from the first three years of the Galaxy And Mass Assembly (GAMA) survey. The magnitude limits of this redshift survey are r < 19.4 mag over two-thirds and 19.8 mag over one-third of the area. The GSMF is determined from a sample of 5210 galaxies using a densitycorrected maximum volume method. This efficiently overcomes the issue of fluctuations in the number density versus redshift. With H0 = 70 km s −1 Mpc −1 , the GSMF is well described

The WiggleZ Dark Energy Survey: survey design and first data release

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 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 Gyr. The target galaxies are selected using ultraviolet (UV) photometry from the Galaxy Evolution Explorer satellite, with a flux limit of NUV < 22.8 mag . We also require that the targets are detected at optical wavelengths, specifically in the range 20.0 < r < 22.5 mag . We use the Lyman break method applied to the UV colours, with additional optical colour limits, to select high-redshift galaxies. The galaxies generally have strong emission lines, permitting reliable redshift measurements in relatively short exposure times on the AAT. The median redshift of the galaxies is z_(med)= 0.6 . The redshift range containing 90 per cent of the galaxies is 0.2 < z < 1.0 . The survey will sample a volume of ~1 Gpc^3 over a projected area on the sky of 1000 deg^2, with an average target density of 350 deg^(−2). Detailed forecasts indicate that the survey will measure the BAO scale to better than 2 per cent and the tangential and radial acoustic wave scales to approximately 3 and 5 per cent, respectively. Combining the WiggleZ constraints with existing cosmic microwave background measurements and the latest supernova data, the marginalized uncertainties in the cosmological model are expected to be σ(Ω_m) = 0.02 and σ(w) = 0.07 (for a constant w model). The WiggleZ measurement of w will constitute a robust, precise and independent test of dark energy models. 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 that 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.

The WiggleZ Dark Energy Survey: the growth rate of cosmic structure since redshift z=0.9

We present precise measurements of the growth rate of cosmic structure for the redshift range 0.1 < z < 0.9, using redshift-space distortions in the galaxy power spectrum of the WiggleZ Dark Energy Survey. Our results, which have a precision of around 10 per cent in four independent redshift bins, are well fitted by a flat Λ cold dark matter (ΛCDM) cosmological model with matter density parameter Ω_m = 0.27. Our analysis hence indicates that this model provides a self-consistent description of the growth of cosmic structure through large-scale perturbations and the homogeneous cosmic expansion mapped by supernovae and baryon acoustic oscillations. We achieve robust results by systematically comparing our data with several different models of the quasi-linear growth of structure including empirical models, fitting formulae calibrated to N-body simulations, and perturbation theory techniques. We extract the first measurements of the power spectrum of the velocity divergence field, P_(θθ) (k), as a function of redshift (under the assumption that P_(gθ) (k) = − √P_(gg)(k)P_(θθ) (k), where g is the galaxy overdensity field), and demonstrate that the WiggleZ galaxy–mass cross-correlation is consistent with a deterministic (rather than stochastic) scale-independent bias model for WiggleZ galaxies for scales k < 0.3 h Mpc^(−1). Measurements of the cosmic growth rate from the WiggleZ Survey and other current and future observations offer a powerful test of the physical nature of dark energy that is complementary to distance–redshift measures such as supernovae and baryon acoustic oscillations.

Galaxy And Mass Assembly (GAMA): stellar mass estimates

This paper describes the first catalogue of photometrically derived stellar mass estimates for intermediate-redshift (z < 0.65; median z= 0.2) galaxies in the Galaxy And Mass Assembly (GAMA) spectroscopic redshift survey. These masses, as well as the full set of ancillary stellar population parameters, will be made public as part of GAMA data release 2. Although the GAMA database does include near-infrared (NIR) photometry, we show that the quality of our stellar population synthesis fits is significantly poorer when these NIR data are included. Further, for a large fraction of galaxies, the stellar population parameters inferred from the optical-plus-NIR photometry are formally inconsistent with those inferred from the optical data alone. This may indicate problems in our stellar population library, or NIR data issues, or both; these issues will be addressed for future versions of the catalogue. For now, we have chosen to base our stellar mass estimates on optical photometry only. In light of our decision to ignore the available NIR data, we examine how well stellar mass can be constrained based on optical data alone. We use generic properties of stellar population synthesis models to demonstrate that restframe colour alone is in principle a very good estimator of stellar mass-to-light ratio, M*/Li. Further, we use the observed relation between restframe (g−i) and M*/Li for real GAMA galaxies to argue that, modulo uncertainties in the stellar evolution models themselves, (g−i) colour can in practice be used to estimate M*/Li to an accuracy of ≲0.1 dex (1σ). This ‘empirically calibrated’ (g−i)–M*/Li relation offers a simple and transparent means for estimating galaxies’ stellar masses based on minimal data, and so provides a solid basis for other surveys to compare their results to z≲0.4 measurements from GAMA.