13,002 research outputs found
HI Epoch of Reionization Arrays
There are few data available with which to constrain the thermal history of
the intergalactic medium (IGM) following global recombination. Thus far, most
constraints flow from analyses of the Cosmic Microwave Background and optical
spectroscopy along a few lines of sight. However, direct study of the IGM in
emission or absorption against the CMB via the 1S hyperfine transition of
Hydrogen would enable broad characterization thermal history and source
populations. New generations of radio arrays are in development to measure this
line signature. Bright foreground emission and the complexity of instrument
calibration models are significant hurdles. How to optimize these is uncertain,
resulting in a diversity in approaches. We discuss recent limits on line
brightness, array efforts including the new Large Aperture Experiment to Detect
the Dark Ages (LEDA), and the next generation Hydrogen Reionization Array
(HERA) concept.Comment: 8 pages, 4 figures, 1 table. Invited review to the 11th Asian-Pacific
Regional IAU Meeting 2011, NARIT Conference Series, Vol. 1 eds. S.
Komonjinda, Y. Kovalev, and D. Ruffolo (2012
B-Mode contamination by synchrotron emission from 3-years WMAP data
We study the contamination of the B-mode of the Cosmic Microwave Background
Polarization (CMBP) by Galactic synchrotron in the lowest emission regions of
the sky. The 22.8-GHz polarization map of the 3-years WMAP data release is used
to identify and analyse such regions. Two areas are selected with
signal-to-noise ratio S/N<2 and S/N<3, covering ~16% and ~26% fraction of the
sky, respectively. The polarization power spectra of these two areas are
dominated by the sky signal on large angular scales (multipoles l < 15), while
the noise prevails on degree scales. Angular extrapolations show that the
synchrotron emission competes with the CMBP B-mode signal for tensor-to-scalar
perturbation power ratio -- at 70-GHz in the 16%
lowest emission sky (S/N<2 area). These values worsen by a factor ~5 in the
S/N<3 region. The novelty is that our estimates regard the whole lowest
emission regions and outline a contamination better than that of the whole high
Galactic latitude sky found by the WMAP team (T/S>0.3). Such regions allow to be measured directly which approximately corresponds to the
limit imposed by using a sky coverage of 15%. This opens interesting
perspectives to investigate the inflationary model space in lowest emission
regions.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
Close kin influences on fertility behavior
Family members are uniquely situated to influence the decision-making of their kin in nearly every facet of life. We examine the importance of social interactions in fertility outcomes by assessing family members’ scope of influence on their fellow kin’s fertility behavior. With the unique KASS genealogical dataset from eight countries in Europe, we study the effects of family members’ fertility outcomes on individual fertility to assess the presence and the extent of inter-generational transmission of fertility behaviors and siblings’ influences on fertility outcomes. We find only limited evidence of the inter-generational transmission of fertility behaviors, but a relatively important effect of siblings for individual fertility. Rather than parents, siblings’ influences appear to constitute the largest share of familial influences on fertility outcomes. We also find that among siblings, women’s fertility is more subject to the influences of their sisters. These findings indicate the relative importance of close kin influences on individual fertility and demonstrate the consequences of family structure for fertility change.Europe, family demography, family size, fertility, kinship, sisters
The synchrotron foreground and CMB temperature-polarization cross correlation power spectrum from the first year WMAP data
We analyse the temperature-polarization cross-correlation in the Galactic
synchrotron template that we have recently developed, and between the template
and CMB temperature maps derived from WMAP data. Since the polarized
synchrotron template itself uses WMAP data, we can estimate residual
synchrotron contamination in the CMB angular spectrum. While
appears to be contamined by synchrotron, no evidence for
contamination is found in the multipole range which is most relevant for the
fit of the cosmological optical depth.Comment: Accepted for pubblication on MNRAS Lette
Post-correlation radio frequency interference classification methods
We describe and compare several post-correlation radio frequency interference
classification methods. As data sizes of observations grow with new and
improved telescopes, the need for completely automated, robust methods for
radio frequency interference mitigation is pressing. We investigated several
classification methods and find that, for the data sets we used, the most
accurate among them is the SumThreshold method. This is a new method formed
from a combination of existing techniques, including a new way of thresholding.
This iterative method estimates the astronomical signal by carrying out a
surface fit in the time-frequency plane. With a theoretical accuracy of 95%
recognition and an approximately 0.1% false probability rate in simple
simulated cases, the method is in practice as good as the human eye in finding
RFI. In addition it is fast, robust, does not need a data model before it can
be executed and works in almost all configurations with its default parameters.
The method has been compared using simulated data with several other mitigation
techniques, including one based upon the singular value decomposition of the
time-frequency matrix, and has shown better results than the rest.Comment: 14 pages, 12 figures (11 in colour). The software that was used in
the article can be downloaded from http://www.astro.rug.nl/rfi-software
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