The local galaxy density field and its effects on the cosmic microwave background
Francis, Caroline Laura
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This thesis presents a reconstruction of the local galaxy density field to a maximum redshift of z = 0.3 from a photometric galaxy catalogue based on the Two Micron All-Sky Survey (2MASS) Extended Source Catalogue (XSC). A Wiener filter approach is adopted for the reconstruction, which is carried out using a basis of spherical harmonics to describe angular variations and spherical Bessel functions to describe the radial part of the field. The angular resolution is fixed at £max = 30 and the radial resolution is set to match this at the characteristic redshift of the survey, z ~ 0.1, resulting in Ar ~ 30/r_1Mpc. A novel technique for replacing missing information from the galactic plane is developed and tested using simulation data, before being applied to the reconstruction of the local density field.This reconstruction is used to predict the contribution to the Cosmic Microwave Background (CMB) of the local Integrated Sachs-Wolfe (ISW) effect and large-scale thermal Sunyaev-Zel’dovich (tSZ) effect. The impact of the predicted local ISW effect on the observed CMB signal is investigated, particularly with regard to reported anomalies on large angular scales. It is found that removal of the predicted local ISW signal to z m£LX = 0.3 from the CMB data can alleviate many of these anomalies.A technique is developed for predicting the large-scale thermal and kinetic Sunyaev- Zel’dovich signals arising from a baryon distribution, when only the corresponding dark matter density and velocity fields are known. This is used in conjunction with the reconstruction of the local density field to predict the large-scale tSZ signal in the Universe. The effect of this signal on the CMB is also analysed, including a discussion of its impact on cosmological parameter estimation and its influence, together with the predicted local ISW signal, on an anomalous cold spot observed in the CMB. Using the predicted large-scale tSZ signal, the prospects for Planck detecting this CMB foreground are examined. It is found that the sensitivity of Planckand its broad frequency range should enable the detection of this signal which is an important test of our preferred cosmological model.A cross-correlation of the photometric redshift 2MASS galaxy data with year-3 WMAP CMB data is performed to attempt to detect the local ISW signal and to investigate whether the addition of photometric redshifts to the 2MASS dataset improves its detection prospects. There is no significant ISW signal found in this analysis, and the expected cross-correlation signal in a ACDM universe is only weakly preferred over no correlation, with likelihood ratio 1.5:1. In this case, the addition of photometric redshifts resulted in no improvement in the detection. The ISW detection prospects of hypothetical future large-scale structure surveys are assessed in conjunction with a ‘best possible’ ISW experiment where one imagines measuring the ISW temperature fluctuations across the whole sky to some zmax. A photometric redshift large- scale structure survey with characteristic redshift z = 0.3 observing ~ 10 million galaxies out to Zmax = 0.7 has reasonable detection prospects, strongly preferring the ACDM hypothesis over a ‘no ISW’ hypothesis in the majority of cases, and with a small (less than 10%) chance of a Type I error at this threshold. The ‘best possible’ experiment with zmax — 0.7 is found to strongly prefer a ACDM hypothesis only 85% of the time, with a 1% chance of such data strongly preferring a ‘no ISW’ hypothesis.