5,131 research outputs found
Detecting the integrated Sachs-Wolfe effect with stacked voids
The stacking of cosmic microwave background (CMB) patches has been recently
used to detect the integrated Sachs-Wolfe effect (iSW). When focusing on the
locations of superstructures identified in the Sloan Digital Sky Survey (SDSS),
Granett et al. (2008a, Gr08) found a signal with strong significance and an
amplitude reportedly higher than expected within the LambdaCDM paradigm. We
revisit the analysis using our own robust protocol, and extend the study to the
two most recent and largest catalogues of voids publicly available. We quantify
and subtract the level of foreground contamination in the stacked images and
determine the contribution on the largest angular scales from the first
multipoles of the CMB. We obtain the radial temperature and photometry profiles
from the stacked images. Using a Monte Carlo approach, we computed the
statistical significance of the profiles for each catalogue and identified the
angular scale at which the signal-to-noise ratio (S/N) is maximum. We
essentially confirm the signal detection reported by Gr08, but for the other
two catalogues, a rescaling of the voids to the same size on the stacked image
is needed to find any significant signal (with a maximum at ~2.4 sigmas). This
procedure reveals that the photometry peaks at unexpectedly large angles in the
case of the Gr08 voids, in contrast to voids from other catalogues. Conversely,
the photometry profiles derived from the stacked voids of these other
catalogues contain small central hot spots of uncertain origin. We also stress
the importance of a posteriori selection effects that might arise when
intending to increase the S/N, and we discuss the possible impact of void
overlap and alignment effects. We argue that the interpretation in terms of an
iSW effect of any detected signal via the stacking method is far from obvious.Comment: 14 pages, 18 figures, 2 tables. Submitted, accepted and published in
A&A ; Minor changes to match the published version of the pape
Entropy Message Passing
The paper proposes a new message passing algorithm for cycle-free factor
graphs. The proposed "entropy message passing" (EMP) algorithm may be viewed as
sum-product message passing over the entropy semiring, which has previously
appeared in automata theory. The primary use of EMP is to compute the entropy
of a model. However, EMP can also be used to compute expressions that appear in
expectation maximization and in gradient descent algorithms.Comment: 5 pages, 1 figure, to appear in IEEE Transactions on Information
Theor
The flux ratio of the [OIII] 5007,4959 lines in AGN: Comparison with theoretical calculations
By taking into account relativistic corrections to the magnetic dipole
operator, the theoretical [OIII] 5006.843/4958.511 line intensity ratio of 2.98
is obtained. In order to check this new value using AGN spectra we present the
measurements of the flux ratio of the [OIII] 4959,5007 emission lines for a
sample of 62 AGN, obtained from the Sloan Digital Sky Survey (SDSS) Database
and from published observations. We select only high signal-to-noise ratio
spectra for which the line shapes of the [OIII] 4959,5007 lines are the same.
We obtained an averaged flux ratio of 2.993 +/- 0.014, which is in a good
agreement with the theoretical one.Comment: Accepted for publication in the MNRA
- …