We present an accurate and fast framework for generating mock catalogues including low-mass halos, based on an implementation of the COmoving Lagrangian Acceleration (COLA) technique. Multiple realisations of mock catalogues are crucial for analyses of large-scale structure, but conventional N-body simulations are too computationally expensive for the production of thousands of realisations. We show that COLA simulations can produce accurate mock catalogues with a moderate computation resource for low- to intermediate- mass galaxies in $10^{12} M_odot$ haloes, both in real and redshift space. COLA simulations have accurate peculiar velocities, without systematic errors in the velocity power spectra for k < 0.15 h/Mpc, and with only 3-per-cent error for k < 0.2 h/Mpc. We use COLA with 10 time steps and a Halo Occupation Distribution to produce 600 mock galaxy catalogues of the WiggleZ Dark Energy Survey. Our parallelized code for efficient generation of accurate halo catalogues is publicly available at github.com/junkoda/cola_halo.
The anisotropic galaxy 2-point correlation function (2PCF) allows measurement of the growth of large-scale structures from the effect of peculiar velocities on the clustering pattern. We present new measurements of the auto- and cross- correlation function multipoles of 69,180 WiggleZ and 46,380 BOSS-CMASS galaxies sharing an overlapping volume of ~0.2 (Gpc/h)^3. Analysing the redshift-space distortions (RSD) of galaxy 2-point statistics for these two galaxy tracers, we test for systematic errors in the modelling depending on galaxy type and investigate potential improvements in cosmological constraints. We build a large number of mock galaxy catalogues to examine the limits of different RSD models in terms of fitting scales and galaxy type, and to study the covariance of the measurements when performing joint fits. For the galaxy data, fitting the monopole and quadrupole of the WiggleZ 2PCF on scales 24<s<80 Mpc/h produces a measurement of the normalised growth rate $fsigma_8$(z=0.54)=0.409$pm$0.059, whereas for the CMASS galaxies we found a consistent constraint of $fsigma_8$(z=0.54)=0.466$pm$0.074. When combining the measurements, accounting for the correlation between the two surveys, we obtain $fsigma_8$(z=0.54)=0.413$pm$0.054, in agreement with the LCDM-GR model of structure growth and with other survey measurements.
We study the large-scale clustering of galaxies in the overlap region of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS sample and the WiggleZ Dark Energy Survey. We calculate the auto-correlation and cross-correlation functions in the overlap region of the two datasets and detect a Baryon Acoustic Oscillation (BAO) signal in each of them. The BAO measurement from the cross-correlation function represents the first such detection between two different galaxy surveys. After applying density-field reconstruction we report distance-scale measurements $D_V r_s^{rm fid} / r_s = (1970 pm 47, 2132 pm 67, 2100 pm 200)$ Mpc from CMASS, the cross-correlation and WiggleZ, respectively. We use correlated mock realizations to calculate the covariance between the three BAO constraints. The distance scales derived from the two datasets are consistent, and are also robust against switching the displacement fields used for reconstruction between the two surveys. This approach can be used to construct a correlation matrix, permitting for the first time a rigorous combination of WiggleZ and CMASS BAO measurements. Using a volume-scaling technique, our result can also be used to combine WiggleZ and future CMASS DR12 results. Finally, we use the cross-correlation function measurements to show that the relative velocity effect, a possible source of systematic uncertainty for the BAO technique, is consistent with zero for our samples.
We investigate the cosmological implications of the latest growth of structure measurement from the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS Data Release 11 with particular focus on the sum of the neutrino masses, $sum m_{ u}$. We examine the robustness of the cosmological constraints from the Baryon Acoustic Oscillation (BAO) scale, the Alcock-Paczynski effect and redshift-space distortions ($D_V/r_s$, $F_{rm AP}$, $fsigma_8$) of citet{Beutler:2013b}, when introducing a neutrino mass in the power spectrum template. We then discuss how the neutrino mass relaxes discrepancies between the Cosmic Microwave Background (CMB) and other low-redshift measurements within $Lambda$CDM. Combining our cosmological constraints with WMAP9 yields $sum m_{ u} = 0.36pm0.14,$eV ($68%$ c.l.), which represents a $2.6sigma$ preference for non-zero neutrino mass. The significance can be increased to $3.3sigma$ when including weak lensing results and other BAO constraints, yielding $sum m_{ u} = 0.35pm0.10,$eV ($68%$ c.l.). However, combining CMASS with Planck data reduces the preference for neutrino mass to $sim 2sigma$. When removing the CMB lensing effect in the Planck temperature power spectrum (by marginalising over $A_{rm L}$), we see shifts of $sim 1sigma$ in $sigma_8$ and $Omega_m$, which have a significant effect on the neutrino mass constraints. In case of CMASS plus Planck without the $A_{rm L}$-lensing signal, we find a preference for a neutrino mass of $sum m_{ u} = 0.34pm 0.14,$eV ($68%$ c.l.), in excellent agreement with the WMAP9+CMASS value. The constraint can be tightened to $3.4sigma$ yielding $sum m_{ u} = 0.36pm 0.10,$eV ($68%$ c.l.) when weak lensing data and other BAO constraints are included.
We analyse the anisotropic clustering of the Baryon Oscillation Spectroscopic Survey (BOSS) CMASS Data Release 11 (DR11) sample, which consists of $690,827$ galaxies in the redshift range $0.43 < z < 0.7$ and has a sky coverage of $8,498,text{deg}^2$. We perform our analysis in Fourier space using a power spectrum estimator suggested by Yamamoto et al. (2006). We measure the multipole power spectra in a self-consistent manner for the first time in the sense that we provide a proper way to treat the survey window function and the integral constraint, without the commonly used assumption of an isotropic power spectrum and without the need to split the survey into sub-regions. The main cosmological signals exploited in our analysis are the Baryon Acoustic Oscillations and the signal of redshift space distortions, both of which are distorted by the Alcock-Paczynski effect. Together, these signals allow us to constrain the distance ratio $D_V(z_{rm eff})/r_s(z_d) = 13.89pm 0.18$, the Alcock-Paczynski parameter $F_{rm AP}(z_{rm eff}) = 0.679pm0.031$ and the growth rate of structure $f(z_{rm eff})sigma_8(z_{rm eff}) = 0.419pm0.044$ at the effective redshift $z_{rm eff}=0.57$. We did not find significant systematic uncertainties for $D_V/r_s$ or $F_{rm AP}$ but include a systematic error for $fsigma_8$ of $3.1%$. Combining our dataset with Planck to test General Relativity (GR) through the simple $gamma$-parameterisation, reveals a $sim 2sigma$ tension between the data and the prediction by GR. The tension between our result and GR can be traced back to a tension in the clustering amplitude $sigma_8$ between CMASS and Planck.
We explore the cosmological implications of the clustering wedges, xi_perp(s) and xi_para(s), of the CMASS Data Release 9 (DR9) sample of the Baryon Oscillation Spectroscopic Survey (BOSS). These clustering wedges are defined by averaging the full two-dimensional correlation function, xi(mu,s), over the ranges 0<mu<0.5 and 0.5<mu<1, respectively. These measurements allow us to constrain the parameter combinations D_A(z)/r_s(z_d)=9.03 +- 0.21 and cz/(r_s(z_d)H(z)) = 12.14 +- 0.43 at the mean redsfhit of the sample, z=0.57. We combine the information from the clustering wedges with recent measurements of CMB, BAO and type Ia supernovae to obtain constraints on the cosmological parameters of the standard LCDM model and a number of potential extensions. The information encoded in the clustering wedges is most useful when the dark energy equation of state is allowed to deviate from its standard LCDM value. The combination of all datasets shows no evidence of a deviation from a constant dark energy equation of state, in which case we find w_DE = -1.013 +- 0.064, in complete agreement with a cosmological constant. We explore potential deviations from general relativity by constraining the growth rate f(z)=d ln D(a)/ d ln a, in which case the combination of the CMASS clustering wedges with CMB data implies f(z=0.57)=0.719 +- 0.094, in accordance with the predictions of GR. Our results clearly illustrate the additional constraining power of anisotropic clustering measurements with respect to that of angle-averaged quantities.
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.
Baryon acoustic oscillations (BAO) at low redshift provide a precise and largely model-independent way to measure the Hubble constant, H0. The 6dF Galaxy Survey measurement of the BAO scale gives a value of H0 = 67 +/- 3.2 km/s/Mpc, achieving a 1-sigma precision of 5%. With improved analysis techniques, the planned WALLABY (HI) and TAIPAN (optical) redshift surveys are predicted to measure H0 to 1-3% precision.
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-sigma 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-of-state 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 Omega_k = -0.004 +/- 0.006.
