7 research outputs found
A Theory of a Spot
We present a simple inflationary scenario that can produce arbitrarily large
spherical underdense or overdense regions embedded in a standard Lambda cold
dark matter paradigm, which we refer to as bubbles. We analyze the effect such
bubbles would have on the Cosmic Microwave Background (CMB). For super-horizon
sized bubble in the vicinity of the last scattering surface, a signal is
imprinted onto CMB via a combination of Sach-Wolfe and an early integrated
Sach-Wolfe (ISW) effects. Smaller, sub-horizon sized bubbles at lower redshifts
(during matter domination and later) can imprint secondary anisotropies on the
CMB via Rees-Sciama, late-time ISW and Ostriker-Vishniac effects. Our scenario,
and arguably most similar inflationary models, produce bubbles which are
over/underdense in potential: in density such bubbles are characterized by
having a distinct wall with the interior staying at the cosmic mean density. We
show that such models can potentially, with only moderate fine tuning, explain
the \emph{cold spot}, a non-Gaussian feature identified in the Wilkinson
Microwave Anisotropy Probe (WMAP) data by several authors. However, more
detailed comparisons with current and future CMB data are necessary to confirm
(or rule out) this scenario.Comment: 19 pages, 19 figures, added references and explanations, JCAP in
pres
The dark flow induced small scale kinetic Sunyaev Zel'dovich effect
Recently Kashlinsky et al. 2008, 2010 reported a discovery of a
km/ bulk flow of the universe out to , through the dark flow
induced CMB dipole in directions of clusters. We point out that, if this dark
flow exists, it will also induce observable CMB temperature fluctuations at
multipole , through modulation of the inhomogeneous electron
distribution on the uniform dark flow. The induced small scale kinetic Sunyaev
Zel'dovich (SZ) effect will reach \sim 1\muk^2 at multipole 10^3\la \ell\la
10^4, only a factor of smaller than the conventional kinetic SZ
effect. Furthermore, it will be correlated with the large scale structure (LSS)
and its correlation with 2MASS galaxy distribution reaches K at
, under a directional dependent optimal weighting scheme. We
estimate that, WMAP plus 2MASS should already be able to detect this dark flow
induced small scale kinetic SZ effect with confidence. Deeper
galaxy surveys such as SDSS can further improve the measurement. Planck plus
existing galaxy surveys can reach \ga 14\sigma detection. Existing CMB-LSS
cross correlation measurements shall be reanalyzed to test the existence of the
dark flow and, if it exists, shall be used to eliminate possible bias on the
integrated Sachs-Wolfe effect measurement through the CMB-LSS cross
correlation.Comment: Minor revisions. 5 pages, 3 figures. MNRAS letters in pres
The Atacama Cosmology Telescope: A Measurement of the 600< ell <8000 Cosmic Microwave Background Power Spectrum at 148 GHz
We present a measurement of the angular power spectrum of the cosmic
microwave background (CMB) radiation observed at 148 GHz. The measurement uses
maps with 1.4' angular resolution made with data from the Atacama Cosmology
Telescope (ACT). The observations cover 228 square degrees of the southern sky,
in a 4.2-degree-wide strip centered on declination 53 degrees South. The CMB at
arcminute angular scales is particularly sensitive to the Silk damping scale,
to the Sunyaev-Zel'dovich (SZ) effect from galaxy clusters, and to emission by
radio sources and dusty galaxies. After masking the 108 brightest point sources
in our maps, we estimate the power spectrum between 600 < \ell < 8000 using the
adaptive multi-taper method to minimize spectral leakage and maximize use of
the full data set. Our absolute calibration is based on observations of Uranus.
To verify the calibration and test the fidelity of our map at large angular
scales, we cross-correlate the ACT map to the WMAP map and recover the WMAP
power spectrum from 250 < ell < 1150. The power beyond the Silk damping tail of
the CMB is consistent with models of the emission from point sources. We
quantify the contribution of SZ clusters to the power spectrum by fitting to a
model normalized at sigma8 = 0.8. We constrain the model's amplitude ASZ < 1.63
(95% CL). If interpreted as a measurement of sigma8, this implies sigma8^SZ <
0.86 (95% CL) given our SZ model. A fit of ACT and WMAP five-year data jointly
to a 6-parameter LCDM model plus terms for point sources and the SZ effect is
consistent with these results.Comment: 15 pages, 8 figures. Accepted for publication in Ap