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Register a new userCosmology with the 6-degree Field Galaxy Survey
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Florian Beutler
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This thesis presents the analysis of the clustering of galaxies in the 6dF Galaxy Survey (6dFGS). At large separation scales the baryon acoustic oscillation (BAO) signal is detected which allows to make an absolute distance measurement at $z_{rm eff} = 0.106$. Such a measurement can be used to constrain the Hubble constant, $H_0 = 67.0pm3.2;$km s$^{-1};$Mpc$^{-1}$ (4.8% precision). Modelling the 2D galaxy correlation function of 6dFGS, $xi(r_p,pi)$, allows a measure of the parameter combination $f(z_{rm eff})sigma_8(z_{rm eff}) = 0.423 pm 0.055$, where $f simeq Omega_m^{gamma}(z)$ is the growth rate of cosmic structure and $sigma_8$ is the r.m.s. of matter fluctuations in $8h^{-1},$Mpc spheres. Such a measurement allows to test the relationship between matter and gravity on cosmic scales by constraining the growth index of density fluctuations, $gamma$. The 6dFGS measurement of $fsigma_8$ combined with WMAP-7, results in $gamma = 0.547 pm 0.088$, consistent with the prediction of General Relativity ($gamma_{rm GR} approx 0.55$). The last chapter of this thesis studies the stellar-mass dependence of galaxy clustering in the 6dF Galaxy Survey. Using the Halo Occupation Distribution (HOD) model, this analysis investigates the trend of dark matter halo mass and satellite fraction with stellar mass by measuring the projected correlation function, $w_p(r_p)$. The findings of this analysis are, that the typical halo mass ($M_1$) as well as the satellite power law index ($alpha$) increase with stellar mass. The 6dFGS results are compared to two different semi-analytic models derived from the Millennium Simulation, as well as weak lensing measurements.
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Low redshift measurements of Baryon Acoustic Oscillations (BAO) test the late time evolution of the Universe and are a vital probe of Dark Energy. Over the past decade both the 6-degree Field Galaxy Survey (6dFGS) and Sloan Digital Sky Survey (SDSS) have provided important distance constraints at $z < 0.3$. In this paper we re-evaluate the cosmological information from the BAO detection in 6dFGS making use of HOD populated COLA mocks for a robust covariance matrix and taking advantage of the now commonly implemented technique of density field reconstruction. For the 6dFGS data, we find consistency with the previous analysis, and obtain an isotropic volume averaged distance measurement of $D_{V}(z_{mathrm{eff}}=0.097) = 372pm17(r_{s}/r_{s}^{mathrm{fid}}),mathrm{Mpc}$, which has a non-Gaussian likelihood outside the $1sigma$ region. We combine our measurement from both the post-reconstruction clustering of 6dFGS and SDSS MGS offering the most robust constraint to date in this redshift regime, $D_{V}(z_{mathrm{eff}}=0.122)=539pm17(r_{s}/r^{mathrm{fid}}_{s}),mathrm{Mpc}$. These measurements are consistent with standard $Lambdamathrm{CDM}$ and after fixing the standard ruler using a Planck prior on $Omega_{m}h^{2}$, the joint analysis gives $H_{0}=64.0pm3.5,mathrm{kms}^{-1}mathrm{Mpc}^{-1}$. In the near future both the Taipan Galaxy Survey and the Dark Energy Spectroscopic Instrument (DESI) will improve this measurement to $1%$ at low redshift.
The peculiar velocities of galaxies cause their redshift-space clustering to depend on the angle to the line-of-sight, providing a key test of gravitational physics on cosmological scales. These effects may be described using a multipole expansion of the clustering measurements. Focussing on Fourier-space statistics, we present a new analysis of the effect of the survey window function, and the variation of the line-of-sight across a survey, on the modelling of power spectrum multipoles. We determine the joint covariance of the Fourier-space multipoles in a Gaussian approximation, and indicate how these techniques may be extended to studies of overlapping galaxy populations via multipole cross-power spectra. We apply our methodology to one of the widest-area galaxy redshift surveys currently available, the 6-degree Field Galaxy Survey, deducing a normalized growth rate f*sigma_8(z=0.06) = 0.38 +/- 0.12 in the low-redshift Universe, in agreement with previous analyses of this dataset using different techniques. Our framework should be useful for processing future wide-angle galaxy redshift surveys.
We present the results of our first year of quasar search in the on-going ESO public Kilo Degree Survey (KiDS) and VISTA Kilo-Degree Infrared Galaxy (VIKING) surveys. These surveys are among the deeper wide-field surveys that can be used to uncovered large numbers of z~6 quasars. This allows us to probe a more common population of z~6 quasars that is fainter than the well-studied quasars from the main Sloan Digital Sky Survey. From this first set of combined survey catalogues covering ~250 deg^2 we selected point sources down to Z_AB=22 that had a very red i-Z (i-Z>2.2) colour. After follow-up imaging and spectroscopy, we discovered four new quasars in the redshift range 5.8<z<6.0. The absolute magnitudes at a rest-frame wavelength of 1450 A are between -26.6 < M_1450 < -24.4, confirming that we can find quasars fainter than M^*, which at z=6 has been estimated to be between M^*=-25.1 and M^*=-27.6. The discovery of 4 quasars in 250 deg^2 of survey data is consistent with predictions based on the z~6 quasar luminosity function. We discuss various ways to push the candidate selection to fainter magnitudes and we expect to find about 30 new quasars down to an absolute magnitude of M_1450=-24. Studying this homogeneously selected faint quasar population will be important to gain insight into the onset of the co-evolution of the black holes and their stellar hosts.
In this paper, we present the tools used to search for galaxy clusters in the Kilo Degree Survey (KiDS), and our first results. The cluster detection is based on an implementation of the optimal filtering technique that enables us to identify clusters as over-densities in the distribution of galaxies using their positions on the sky, magnitudes, and photometric redshifts. The contamination and completeness of the cluster catalog are derived using mock catalogs based on the data themselves. The optimal signal to noise threshold for the cluster detection is obtained by randomizing the galaxy positions and selecting the value that produces a contamination of less than 20%. Starting from a subset of clusters detected with high significance at low redshifts, we shift them to higher redshifts to estimate the completeness as a function of redshift: the average completeness is ~ 85%. An estimate of the mass of the clusters is derived using the richness as a proxy. We obtained 1858 candidate clusters with redshift 0 < z_c < 0.7 and mass 13.5 < log(M500/Msun) < 15 in an area of 114 sq. degrees (KiDS ESO-DR2). A comparison with publicly available Sloan Digital Sky Survey (SDSS)-based cluster catalogs shows that we match more than 50% of the clusters (77% in the case of the redMaPPer catalog). We also cross-matched our cluster catalog with the Abell clusters, and clusters found by XMM and in the Planck-SZ survey; however, only a small number of them lie inside the KiDS area currently available.
We simulate the scientific performance of the Wide-Field Infrared Survey Telescope (WFIRST) High Latitude Survey (HLS) on dark energy and modified gravity. The 1.6 year HLS Reference survey is currently envisioned to image 2000 deg$^2$ in multiple bands to a depth of $sim$26.5 in Y, J, H and to cover the same area with slit-less spectroscopy beyond z=3. The combination of deep, multi-band photometry and deep spectroscopy will allow scientists to measure the growth and geometry of the Universe through a variety of cosmological probes (e.g., weak lensing, galaxy clusters, galaxy clustering, BAO, Type Ia supernova) and, equally, it will allow an exquisite control of observational and astrophysical systematic effects. In this paper we explore multi-probe strategies that can be implemented given WFIRSTs instrument capabilities. We model cosmological probes individually and jointly and account for correlated systematics and statistical uncertainties due to the higher order moments of the density field. We explore different levels of observational systematics for the WFIRST survey (photo-z and shear calibration) and ultimately run a joint likelihood analysis in N-dim parameter space. We find that the WFIRST reference survey alone (no external data sets) can achieve a standard dark energy FoM of >300 when including all probes. This assumes no information from external data sets and realistic assumptions for systematics. Our study of the HLS reference survey should be seen as part of a future community driven effort to simulate and optimize the science return of WFIRST.
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