9 research outputs found
Small-Angle CMB Temperature Anisotropies Induced by Cosmic Strings
We use Nambu-Goto numerical simulations to compute the cosmic microwave
background (CMB) temperature anisotropies induced at arcminute angular scales
by a network of cosmic strings in a Friedmann-Lemaitre-Robertson-Walker (FLRW)
expanding universe. We generate 84 statistically independent maps on a 7.2
degree field of view, which we use to derive basic statistical estimators such
as the one-point distribution and two-point correlation functions. At high
multipoles, the mean angular power spectrum of string-induced CMB temperature
anisotropies can be described by a power law slowly decaying as \ell^{-p}, with
p=0.889 (+0.001,-0.090) (including only systematic errors). Such a behavior
suggests that a nonvanishing string contribution to the overall CMB
anisotropies may become the dominant source of fluctuations at small angular
scales. We therefore discuss how well the temperature gradient magnitude
operator can trace strings in the context of a typical arcminute
diffraction-limited experiment. Including both the thermal and nonlinear
kinetic Sunyaev-Zel'dovich effects, the Ostriker-Vishniac effect, and the
currently favored adiabatic primary anisotropies, we find that, on such a map,
strings should be ``eye visible,'' with at least of order ten distinctive
string features observable on a 7.2 degree gradient map, for tensions U down to
GU \simeq 2 x 10^{-7} (in Planck units). This suggests that, with upcoming
experiments such as the Atacama Cosmology Telescope (ACT), optimal
non-Gaussian, string-devoted statistical estimators applied to small-angle CMB
temperature or gradient maps may put stringent constraints on a possible cosmic
string contribution to the CMB anisotropies.Comment: 17 pages, 9 figures. v2: matches published version, minor
clarifications added, typo in Eq. (8) fixed, results unchange
Evidence for Spatial Separation of Galactic Dust Components
We present an implementation of a Bayesian mixture model using Hamiltonian
Monte Carlo (HMC) techniques to search for spatial separation of Galactic dust
components. Utilizing intensity measurements from \Planck High Frequency
Instrument (HFI), we apply this model to high-latitude Galactic dust emission.
Our analysis reveals a strong preference for a spatially-varying two-population
dust model in intensity, with each population being well characterized by a
single-component dust spectral-energy distribution (SED). While no spatial
information is built into the likelihood, our investigation unveils spatially
coherent structures with high significance, pointing to a physical origin for
the observed spatial separation. These results are robust to our choice of
likelihood and of input data. Furthermore, they are favored over a
single-component dust model by Bayesian evidence calculations.
Incorporating \IRAS 100\, to constrain the Wein-side of the blackbody
function, we find the dust populations differ at the level on the
spectral index () vs. temperature plane. The presence of a
multi-population dust has implications for component separation techniques
frequently employed in the recovery of the Cosmic Microwave Background.Comment: 16 pages, 8 figures. Submitted to Ap