772 research outputs found
Interpreting CMB Anisotropy Observations: Trying to Tell the Truth with Statistics
A conflict has been reported between the baryon density inferred from
deuterium observations and that found from recent CMB observations by BOOMERanG
and MAXIMA. Despite the flurry of papers that attempt to resolve this conflict
by adding new physics to the early universe, we will show that it can instead
be resolved via a more careful usage of statistics. Indeed, the Bayesian
analyses that produce this conflict are by their nature poorly suited for
drawing this type of conclusion. A properly defined frequentist analysis can
address this question directly and appears not to find a conflict. Finally, a
conservative accounting of systematic uncertainties in measuring the deuterium
abundance could reduce what is nominally a 3 sigma conflict to 1 sigma.Comment: 6 pages, to appear in proceedings of the 20th Texas Symposium on
Relativistic Astrophysic
Evidence for Spatially Compact Lyman Alpha Emission in z=3.1 Lyman-Alpha-Emitting Galaxies
We present the results of a high-spatial-resolution study of the line
emission in a sample of z=3.1 Lyman-Alpha-Emitting Galaxies (LAEs) in the
Extended Chandra Deep Field-South. Of the eight objects with coverage in our
HST/WFPC2 narrow-band imaging, two have clear detections and an additional two
are barely detected (~2-sigma). The clear detections are within ~0.5 kpc of the
centroid of the corresponding rest-UV continuum source, suggesting that the
line-emitting gas and young stars in LAEs are spatially coincident. The
brightest object exhibits extended emission with a half-light radius of ~1.5
kpc, but a stack of the remaining LAE surface brightness profiles is consistent
with the WFPC2 point spread function. This suggests that the Lyman Alpha
emission in these objects originates from a compact (<~2 kpc) region and cannot
be significantly more extended than the far-UV continuum emission (<~1 kpc).
Comparing our WFPC2 photometry to previous ground-based measurements of their
monochromatic fluxes, we find at 95% (99.7%) confidence that we cannot be
missing more than 22% (32%) of the Lyman Alpha emission.Comment: 4 pages, 3 figures, accepted to ApJ letter
From the Cosmological Microwave Background to Large-Scale Structure
The shape of the primordial fluctuation spectrum is probed by cosmic
microwave background fluctuations which measure density fluctuations at z~1000
on scales of hundreds of Mpc and from galaxy redshift surveys, which measure
structure at low redshift out to several hundred Mpc. The currently acceptable
library of cosmological models is inadequate to account for the current data,
and more exotic models must be sought. New data sets such as SDSS and 2DF are
urgently needed to verify whether the shape discrepancies in P(k) will persist.Comment: 11 pages including 4 color figures, to appear in Proc. of Nobel
Symposium- Particle Physics and the Universe, Physica Script
Extracting Primordial Density Fluctuations
The combination of detections of anisotropy in the Cosmic Microwave
Background radiation and observations of the large-scale distribution of
galaxies probes the primordial density fluctuations of the universe on spatial
scales varying by three orders of magnitude. These data are found to be
inconsistent with the predictions of several popular cosmological models.
Agreement between the data and the Cold + Hot Dark Matter model, however,
suggests that a significant fraction of the matter in the universe may consist
of massive neutrinos.Comment: 20 pages including 4 color postscript figures. Full-size figures and
data compilation available at
http://cfpa.berkeley.edu/cmbserve/fluctuations/figures.htm
A Simultaneous Stacking and Deblending Algorithm for Astronomical Images
Stacking analysis is a means of detecting faint sources using a priori
position information to estimate an aggregate signal from individually
undetected objects. Confusion severely limits the effectiveness of stacking in
deep surveys with limited angular resolution, particularly at far infrared to
submillimeter wavelengths, and causes a bias in stacking results. Deblending
corrects measured fluxes for confusion from adjacent sources; however, we find
that standard deblending methods only reduce the bias by roughly a factor of
two while tripling the variance. We present an improved algorithm for
simultaneous stacking and deblending that greatly reduces bias in the flux
estimate with nearly minimum variance. When confusion from neighboring sources
is the dominant error, our method improves upon RMS error by at least a factor
of three and as much as an order of magnitude compared to other algorithms.
This improvement will be useful for Herschel and other telescopes working in a
source confused, low signal to noise regime.Comment: accepted to The Astronomical Journal. 18 pages, 6 figure
SED fitting with MCMC: methodology and application to large galaxy surveys
We present GalMC (Acquaviva et al 2011), our publicly available Markov Chain
Monte Carlo algorithm for SED fitting, show the results obtained for a stacked
sample of Lyman Alpha Emitting galaxies at z ~ 3, and discuss the dependence of
the inferred SED parameters on the assumptions made in modeling the stellar
populations. We also introduce SpeedyMC, a version of GalMC based on
interpolation of pre-computed template libraries. While the flexibility and
number of SED fitting parameters is reduced with respect to GalMC, the average
running time decreases by a factor of 20,000, enabling SED fitting of each
galaxy in about one second on a 2.2GHz MacBook Pro laptop, and making SpeedyMC
the ideal instrument to analyze data from large photometric galaxy surveys.Comment: Proceedings of the IAU Symposium 284, "The Spectral Energy
Distribution of galaxies"; typos fixed; refs adde
- …