14,487 research outputs found
Prospects for weak lensing studies with new radio telescopes
I outline the prospects for performing weak lensing studies with the new
generation of radio telescopes that are coming online now and in the future. I
include a description of a proposed technique to use polarization observations
in radio weak lensing analyses which could prove extremely useful for removing
a contaminating signal from intrinsic alignments. Ultimately, the Square
Kilometre Array promises to be an exceptional instrument for performing weak
lensing studies due to the high resolution, large area surveys which it will
perform. In the nearer term, the e-MERLIN instrument in the UK offers the high
sensitivity and sub-arcsec resolution required to prove weak lensing techniques
in the radio band. I describe the SuperCLASS survey -- a recently accepted
e-MERLIN legacy programme which will perform a pioneering radio weak lensing
analysis of a supercluster of galaxies.Comment: to appear in the proceedings of the 2012 Moriond cosmology meetin
Foreground removal for Square Kilometre Array observations of the Epoch of Reionization with the Correlated Component Analysis
We apply the Correlated Component Analysis (CCA) method on simulated data of
the Square Kilometre Array, with the aim of accurately cleaning the 21 cm
reionization signal from diffuse foreground contamination. The CCA has been
developed for the Cosmic Microwave Background, but the application of the
Fourier-domain implementation of this method to the reionization signal is
straightforward.
The CCA is a parametric method to estimate the frequency behaviour of the
foregrounds from the data by using second-order statistics. We test its
performance on foreground simulations of increasing complexity, designed to
challenge the parametric models adopted. We also drop the assumption of
spectral smoothness that most of the methods rely upon. We are able to clean
effectively the simulated data across the explored frequency range (100-200
MHz) for all the foreground simulations. This shows that the CCA method is very
promising for EoR component separation.Comment: 12 pages, 15 figures, accepted by MNRA
Cross-correlation cosmic shear with the SDSS and VLA FIRST surveys
We measure the cosmic shear power spectrum on large angular scales by
cross-correlating the shapes of ~9 million galaxies measured in the optical
SDSS survey with the shapes of ~2.7x10^5 radio galaxies measured by the
overlapping VLA-FIRST survey. Our measurements span the multipole range 10 < l
< 130, corresponding to angular scales 2deg < {\theta} < 20deg. On these
scales, the shear maps from both surveys suffer from significant systematic
effects that prohibit a measurement of the shear power spectrum from either
survey alone. Conversely we demonstrate that a power spectrum measured by
cross-correlating the two surveys is unbiased.
We measure an E-mode power spectrum from the data that is inconsistent with
zero signal at the 99\% confidence (~2.7{\sigma}) level. The odd-parity B-mode
signal and the EB cross- correlation are both found to be consistent with zero
(within 1{\sigma}). These constraints are obtained after a careful error
analysis that accounts for uncertainties due to cosmic variance, random galaxy
shape noise and shape measurement errors, as well as additional errors
associated with the observed large-scale systematic effects in the two surveys.
Our constraints are consistent with the expected signal in the concordance
cosmological model assuming recent estimates of the cosmological parameters
from the Planck satellite, and literature values for the median redshifts of
the SDSS and FIRST galaxy populations.
The cross-power spectrum approach described in this paper represents a
powerful technique for mitigating shear systematics and will be ideal for
extracting robust results, with the exquisite control of systematics required,
from future cosmic shear surveys with the SKA, LSST, Euclid and WFIRST-AFTA.Comment: 19 pages, 19 figure
Galaxy-galaxy and galaxy-cluster lensing with the SDSS and FIRST surveys
We perform a galaxy-galaxy lensing study by correlating the shapes of
2.7 10 galaxies selected from the VLA FIRST radio survey
with the positions of 38.5 million SDSS galaxies, 132000 BCGs and
78000 SDSS galaxies that are also detected in the VLA FIRST survey. The
measurements are conducted on angular scales 1200 arcsec.
On scales 200 arcsec we find that the measurements are
corrupted by residual systematic effects associated with the instrumental beam
of the VLA data. Using simulations we show that we can successfully apply a
correction for these effects. Using the three lens samples (the SDSS DR10
sample, the BCG sample and the SDSS-FIRST matched object sample) we measure a
tangential shear signal that is inconsistent with zero at the 10,
3.8 and 9 level respectively. Fitting an NFW model to the
detected signals we find that the ensemble mass profile of the BCG sample
agrees with the values in the literature. However, the mass profiles of the
SDSS DR10 and the SDSS-FIRST matched object samples are found to be shallower
and steeper than results in the literature respectively. The best-fitting
Virial masses for the SDSS DR10, BCG and SDSS-FIRST matched samples, derived
using an NFW model and allowing for a varying concentration factor, are
M = (1.2 0.4) 10M,
M = (1.4 1.3) 10M and
M = 8.0 4.2 10M
respectively. These results are in good agreement (within 2)
with values in the literature. Our findings suggest that for galaxies to be
both bright in the radio and in the optical they must be embedded in very dense
environment on scales R 1Mpc.Comment: 15 pages, 9 figures and 2 table
SKA Engineering Change Proposal: Gridded Visibilities to Enable Precision Cosmology with Radio Weak Lensing
This document was submitted as supporting material to an Engineering Change
Proposal (ECP) for the Square Kilometre Array (SKA). This ECP requests gridded
visibilities as an extra imaging data product from the SKA, in order to enable
bespoke analysis techniques to measure source morphologies to the accuracy
necessary for precision cosmology with radio weak lensing. We also discuss the
properties of an SKA weak lensing data set and potential overlaps with other
cosmology science goals.Comment: Comments welcome. 4 pages, 3 figures. Progress can be tracked at the
SKA ECP register https://skaoffice.atlassian.net/wiki/display/EP/ECP+Registe
The Mass of Dwarf Planet Eris
The discovery of dwarf planet Eris was followed shortly by the discovery of its satellite, Dysnomia, but the satellite orbit, and thus the system mass, was not known. New observations with the Keck Observatory and the Hubble Space Telescopes show that Dysnomia has a circular orbit with a radius of 37,350 ± 140 (1-σ) kilometers and a 15.774 ± 0.002 day orbital period around Eris. These orbital parameters agree with expectations for a satellite formed out of the orbiting debris left from a giant impact. The mass of Eris from these orbital parameters is 1.67 × 10^(22) ± 0.02 × 10^(22) kilograms, or 1.27 ± 0.02 that of Pluto
Radio-Optical Galaxy Shape Correlations in the COSMOS Field
We investigate the correlations in galaxy shapes between optical and radio
wavelengths using archival observations of the COSMOS field. Cross-correlation
studies between different wavebands will become increasingly important for
precision cosmology as future large surveys may be dominated by systematic
rather than statistical errors. In the case of weak lensing, galaxy shapes must
be measured to extraordinary accuracy (shear systematics of ) in
order to achieve good constraints on dark energy parameters. By using shape
information from overlapping surveys in optical and radio bands, robustness to
systematics may be significantly improved without loss of constraining power.
Here we use HST-ACS optical data, VLA radio data, and extensive simulations to
investigate both our ability to make precision measurements of source shapes
from realistic radio data, and to constrain the intrinsic astrophysical scatter
between the shapes of galaxies as measured in the optical and radio wavebands.
By producing a new image from the VLA-COSMOS L-band radio visibility data that
is well suited to galaxy shape measurements, we are able to extract precise
measurements of galaxy position angles. Comparing to corresponding measurements
from the HST optical image, we set a lower limit on the intrinsic astrophysical
scatter in position angles, between the optical and radio bands, of
radians (or ) at a confidence
level.Comment: 17 pages, 13 figure, 5 tables. Updated to match published version
with a number of typographical correction
Separating weak lensing and intrinsic alignments using radio observations
We discuss methods for performing weak lensing using radio observations to
recover information about the intrinsic structural properties of the source
galaxies. Radio surveys provide unique information that can benefit weak
lensing studies, such as HI emission, which may be used to construct galaxy
velocity maps, and polarized synchrotron radiation; both of which provide
information about the unlensed galaxy and can be used to reduce galaxy shape
noise and the contribution of intrinsic alignments. Using a proxy for the
intrinsic position angle of an observed galaxy, we develop techniques for
cleanly separating weak gravitational lensing signals from intrinsic alignment
contamination in forthcoming radio surveys. Random errors on the intrinsic
orientation estimates introduce biases into the shear and intrinsic alignment
estimates. However, we show that these biases can be corrected for if the error
distribution is accurately known. We demonstrate our methods using simulations,
where we reconstruct the shear and intrinsic alignment auto and cross-power
spectra in three overlapping redshift bins. We find that the intrinsic position
angle information can be used to successfully reconstruct both the lensing and
intrinsic alignment power spectra with negligible residual bias.Comment: 17 pages, 10 figures, submitted to MNRA
A new model of the microwave polarized sky for CMB experiments
We present a new model of the microwave sky in polarization that can be used
to simulate data from CMB polarization experiments. We exploit the most recent
results from the Planck satellite to provide an accurate description of the
diffuse polarized foreground synchrotron and thermal dust emission. Our model
can include the two mentioned foregrounds, and also a constructed template of
Anomalous Microwave Emission (AME). Several options for the frequency
dependence of the foregrounds can be easily selected, to reflect our
uncertainties and to test the impact of different assumptions. Small angular
scale features can be added to the foreground templates to simulate
high-resolution observations. We present tests of the model outputs to show the
excellent agreement with Planck and WMAP data. We determine the range within
which the foreground spectral indices can be varied to be consistent with the
current data. We also show forecasts for a high-sensitivity, high-resolution
full-sky experiment such as the Cosmic ORigin Explorer (COrE). Our model is
released as a python script that is quick and easy to use, available at
\url{http://www.jb.man.ac.uk/~chervias}.Comment: 12 pages, 14 Figures, 1 Table, Accepted by MNRA
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