Abstract
The Cosmic Microwave Background (CMB) is the faint afterglow of the extreme conditions that existed shortly after Big Bang. The temperature of the CMB radiation across the sky is extremely uniform, yet tiny anisotropies are present, and have with recent satellite missions been mapped to very high accuracy. The information which the CMB provides has helped in creating the current standard cosmological model - the CDM model - and the theory of cosmic inflation as well as constrain a vast amount of cosmological parameters. The accuracy of observations of the CMB radiation is thus of extreme importance for modern Cosmology. Ever since the first easurements of the CMB anisotropy, several anomalies have been reported, and subsequently confirmed by later satellite, ground and balloon based missions. These anomalies does not conform to the standard model of cosmic inflation, and may thereby jeopardize the model itself and the derived cosmological
parameters, upon which most of the current astronomy and cosmology
rests. In order to ascertain whether the anomalies are the results of systematics from the instruments, incomplete data treatment, residuals from foregrounds affecting the measurement of the true CMB signal, or is indeed artifacts in the true CMB signal itself, a substantial work is needed, and is indeed ongoing.
This thesis focuses on several tests of CMB anisotropies, and attempts of clarifying or detailing the contributions from new, hitherto uncounted foregrounds.
The thesis focuses on the following tests:
A comparison of the WMAP map and the recently released Planck map, as well as tests between the respective years of WMAP data and various products from Planck. By subtracting two CMB maps, the difference map should contain only contaminants which differ between the two CMB maps. By cross correlating each map with this difference map, one may ascertain the level of the contamination of each map. We find that the ILC9 product from the WMAP team is contaminated compared to the previous edition (the ILC7 map). Likewise a comparison between the ILC9 map and 3 maps from Planck show, that ILC9 is contaminated to a high degree compared to Planck and to 10000 simulated maps. A test of the distribution of the phases of the spherical harmonic decomposition of the CMB. We compare a random walk of the phases by only considering the phases of even and odd multipoles respectively. Expanding on this we also tested the results in both ecliptic and Galactic coordinates. We found that there is a significant difference between the phases of the even and odd multipoles, both when only considering the phases, but also a clear difference when looking at a random walk test.
An investigation of certain peculiar symmetries found upon the CMB anisotropy sky. We would not expect the Galactic plane nor the Galactic center to have any special symmetric representation in a CMB map. We test for these assumptions and for a further rotation in the -direction using the octupole of CMB data and compare to simulated data. Further we investigate, via an estimator based on the power spectrum, which multipoles seems most peculiar from a symmetric point of view, compared to simulations. We find that the most anomalous spherical harmonic order of the octupole carry very low power compared to simulated data, and further that several multipoles show a distinct deviation compared to simulations when comparing the power spectrum drawn from the most anomalous spherical harmonic orders of the CMB signal.
A thorough test of the CMB parity asymmetry. We show that the CMB sky
contain a signicant parity asymmetry between even and odd multipoles, and
investigate possible causes for this asymmetry. Further we test what the implications are, if we extract cosmological parameters from only the even or the odd multipoles. Additionally we test the lack of angular correlations on large scales, and found it to be phenomenologically connected with the parity asymmetry. A brief set of results for the parity asymmetry for the 4 data sets from the Planck satellite. This is compared with simulations to show how anomalous the observed low value of the parity asymmetry is.
A test devoted to investigating whether the Edgeworth-Kuiper belt can aect
the observed CMB signal. We assume that emission from the Kuiper belt around the solar system in combination with a dipole modulation of the signal due to an unknown systematic effect may explain both the observed parity asymmetry, as well as the peculiar alignment of the quadrupole and octupole. We find, that with our model of the Kuiper belt objects, and for specic directions of dipole modulation, we can reduce the eects of the parity asymmetry, as well as mitigate the observed alignment between the quadrupole and octupole.
An investigation into the possible effects of the Galactic magnetic field, and the way it may affect the observed CMB signal on the sky. The map of Faraday depth traces out the regions of strong magnetic fields, where synchrotron radiation may give o radiation which can be taken for a CMB signal. These areas are in some cases well above the Galactic plane, and may constitute so far unaccounted foregrounds for the CMB. By cross correlating the CMB signal and the Faraday depth map, we investigate whether the two signals share any common features. Especially we focus our interest around the CMB Cold Spot, and the 6 Galactic radio loops, which are likely remnants of old supernova explosions. We find similar morphological structures in the CMB and the Faraday depth maps, especially at the CMB cold spot area, and other areas of extreme correlations, hinting that the CMB map may be contaminated by the eects of the physical quantities (thermal electron density and the Galactic magnetic eld) measured by the Faraday depth.
parameters, upon which most of the current astronomy and cosmology
rests. In order to ascertain whether the anomalies are the results of systematics from the instruments, incomplete data treatment, residuals from foregrounds affecting the measurement of the true CMB signal, or is indeed artifacts in the true CMB signal itself, a substantial work is needed, and is indeed ongoing.
This thesis focuses on several tests of CMB anisotropies, and attempts of clarifying or detailing the contributions from new, hitherto uncounted foregrounds.
The thesis focuses on the following tests:
A comparison of the WMAP map and the recently released Planck map, as well as tests between the respective years of WMAP data and various products from Planck. By subtracting two CMB maps, the difference map should contain only contaminants which differ between the two CMB maps. By cross correlating each map with this difference map, one may ascertain the level of the contamination of each map. We find that the ILC9 product from the WMAP team is contaminated compared to the previous edition (the ILC7 map). Likewise a comparison between the ILC9 map and 3 maps from Planck show, that ILC9 is contaminated to a high degree compared to Planck and to 10000 simulated maps. A test of the distribution of the phases of the spherical harmonic decomposition of the CMB. We compare a random walk of the phases by only considering the phases of even and odd multipoles respectively. Expanding on this we also tested the results in both ecliptic and Galactic coordinates. We found that there is a significant difference between the phases of the even and odd multipoles, both when only considering the phases, but also a clear difference when looking at a random walk test.
An investigation of certain peculiar symmetries found upon the CMB anisotropy sky. We would not expect the Galactic plane nor the Galactic center to have any special symmetric representation in a CMB map. We test for these assumptions and for a further rotation in the -direction using the octupole of CMB data and compare to simulated data. Further we investigate, via an estimator based on the power spectrum, which multipoles seems most peculiar from a symmetric point of view, compared to simulations. We find that the most anomalous spherical harmonic order of the octupole carry very low power compared to simulated data, and further that several multipoles show a distinct deviation compared to simulations when comparing the power spectrum drawn from the most anomalous spherical harmonic orders of the CMB signal.
A thorough test of the CMB parity asymmetry. We show that the CMB sky
contain a signicant parity asymmetry between even and odd multipoles, and
investigate possible causes for this asymmetry. Further we test what the implications are, if we extract cosmological parameters from only the even or the odd multipoles. Additionally we test the lack of angular correlations on large scales, and found it to be phenomenologically connected with the parity asymmetry. A brief set of results for the parity asymmetry for the 4 data sets from the Planck satellite. This is compared with simulations to show how anomalous the observed low value of the parity asymmetry is.
A test devoted to investigating whether the Edgeworth-Kuiper belt can aect
the observed CMB signal. We assume that emission from the Kuiper belt around the solar system in combination with a dipole modulation of the signal due to an unknown systematic effect may explain both the observed parity asymmetry, as well as the peculiar alignment of the quadrupole and octupole. We find, that with our model of the Kuiper belt objects, and for specic directions of dipole modulation, we can reduce the eects of the parity asymmetry, as well as mitigate the observed alignment between the quadrupole and octupole.
An investigation into the possible effects of the Galactic magnetic field, and the way it may affect the observed CMB signal on the sky. The map of Faraday depth traces out the regions of strong magnetic fields, where synchrotron radiation may give o radiation which can be taken for a CMB signal. These areas are in some cases well above the Galactic plane, and may constitute so far unaccounted foregrounds for the CMB. By cross correlating the CMB signal and the Faraday depth map, we investigate whether the two signals share any common features. Especially we focus our interest around the CMB Cold Spot, and the 6 Galactic radio loops, which are likely remnants of old supernova explosions. We find similar morphological structures in the CMB and the Faraday depth maps, especially at the CMB cold spot area, and other areas of extreme correlations, hinting that the CMB map may be contaminated by the eects of the physical quantities (thermal electron density and the Galactic magnetic eld) measured by the Faraday depth.
| Original language | English |
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| Publisher | The Niels Bohr Institute, Faculty of Science, University of Copenhagen |
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| Publication status | Published - 2013 |