Stardust and Cosmology

Abstract

Over the past 30 years, the cosmic microwave background (CMB) has profoundly influenced our understanding of the history of our universe and ushered in an era of precision cosmology. The spatial anisotropy (both polarized and unpolarized) has been the focus of both experiment and theory, and has driven the field forward. One of the next frontiers of CMB science is the study of the spectral distortions of the CMB. Primordial spectral distortions of the CMB are sensitive to energy injection by exotic physics in the early universe. The proposed Primordial Inflation Explorer (PIXIE) mission has the raw sensitivity to provide meaningful limits on new physics, but only if foreground emission can be adequately modeled. In this thesis, I analyse the impact of including galactic dust and cosmic infrared background modeling on CMB spectral distortion detection, while still expecting PIXIE to constrain synchrotron, free-free emission, and the spectral distortion from the blackbody temperature deviation. In order to adequately model the dust foreground, I also focus on exploring the properties of galactic dust. Dust is an important component of the interstellar medium, forming structures in the space between the stars in our galaxy. Dust is formed through the death process of stars, through supernovas or stellar winds. It is composed of elements that have formed in the stars, and it plays an important role in the further formation of complex molecules. The size and composition of dust grains is spatially variable within our galaxy, and possibly across cosmic time. We have ideas about the chief constituents of dust, but detailed knowledge is elusive. I study the effect of variations in dust size distribution and composition on the correlation between the spectral shape of extinction (parameterized by R(V)) and far-infrared dust emissivity (parameterized by the power-law index β). Starting from the size distribution models, using the dust absorption and emission properties for carbonaceous, silicate, and polycyclic aromatic hydrocarbon grains, I calculate the extinction and constrain it to agree with the observed reddening vector. I find that larger grains are correlated with high R(V). However, this trend is not enough to explain the emission-extinction correlation observed in data. For the R (V)−β correlation to arise, I need to impose explicit priors for the carbonaceous and silicate volume priors as functions of R(V). The results show that a composition with higher ratio of carbonaceous to silicate grains leads to higher R(V) and lower β. A relation between E(B−V)/τ353 and R(V) is apparent, with possible consequences for the recalibration of emission-based dust maps as a function of R(V). Finally, for this thesis, I create the first 3 dimensional map of the temperature of the dust in the interstellar medium. Having a better understanding of the 3D dust can help us characterize the 3D structure of the magnetic field, and compute the six-dimensional phase-space density of the interstellar radiation field (the amount of light in every 3D voxel, in every direction, at every energy). Obtaining this data would allow us to see the Galaxy from any vantage point, at any angle, in any color. This would provide a critical element in the model of the diffuse Galactic gamma-ray emission, and thus to gamma ray astronomy, in particular to dark matter annihilation. In addition, the 3D dust analysis in the galactic plane can provide us with critical information about correlation in dust properties, which can be used to inform the analysis at higher latitudes for PIXIE and other experiments. It is thus critical that I improve our characterisation of the dust, both for improving our knowledge of the ISM, and for CMB experiments.