218 research outputs found
The Sensitivity of First Generation Epoch of Reionization Observatories and Their Potential for Differentiating Theoretical Power Spectra
Statistical observations of the epoch of reionization (EOR) power spectrum
provide a rich data set for understanding the transition from the cosmic "dark
ages" to the ionized universe we see today. EOR observations have become an
active area of experimental cosmology, and three first generation
observatories--MWA, PAST, and LOFAR--are currently under development. In this
paper we provide the first quantitative calculation of the three dimensional
power spectrum sensitivity, incorporating the design parameters of a planned
array. This calculation is then used to explore the constraints these first
generation observations can place on the EOR power spectrum. The results
demonstrate the potential of upcoming power spectrum observations to constrain
theories of structure formation and reionization.Comment: 7 pages with 5 figures. Submitted to Ap
A multipole-Taylor expansion for the potential of gravitational lens MG J0414+0534
We employ a multipole-Taylor expansion to investigate how tightly the
gravitational potential of the quadruple-image lens MG J0414+0534 is
constrained by recent VLBI observations. These observations revealed that each
of the four images of the background radio source contains four distinct
components, thereby providing more numerous and more precise constraints on the
lens potential than were previously available. We expand the two-dimensional
lens potential using multipoles for the angular coordinate and a modified
Taylor series for the radial coordinate. After discussing the physical
significance of each term, we compute models of MG J0414+0534 using only VLBI
positions as constraints. The best-fit model has both interior and exterior
quadrupole moments as well as exterior m=3 and m=4 multipole moments. The
deflector centroid in the models matches the optical galaxy position, and the
quadrupoles are aligned with the optical isophotes. The radial distribution of
mass could not be well constrained. We discuss the implications of these models
for the deflector mass distribution and for the predicted time delays between
lensed components.Comment: 44 pages, 5 figures, 11 tables, accepted for publication in Ap
Direct optimal mapping for 21 cm cosmology: A demonstration with the hydrogen epoch of reionization array
Motivated by the desire for wide-field images with well-defined statistical properties for 21 cm cosmology, we implement an optimal mapping pipeline that computes a maximum likelihood estimator
for the sky using the interferometric measurement equation. We demonstrate this “direct optimal
mapping” with data from the Hydrogen Epoch of Reionization (HERA) Phase I observations. After
validating the pipeline with simulated data, we develop a maximum likelihood figure-of-merit for comparing four sky models at 166 MHz with a bandwidth of 100 kHz. The HERA data agree with the
GLEAM catalogs (Wayth et al. 2015) to < 10%. After subtracting the GLEAM point sources, the
HERA data discriminate between the different continuum sky models, providing most support for the
model of Byrne et al. (2021). We report the computation cost for mapping the HERA Phase I data and
project the computation for the HERA 320-antenna data; both are feasible with a modern server. The
algorithm is broadly applicable to other interferometers and is valid for wide-field and non-coplanar
arrays
Toward Empirical Constraints on the Global Redshifted 21 cm Brightness Temperature During the Epoch of Reionization
Preliminary results are presented from a simple, single-antenna experiment
designed to measure the all-sky radio spectrum between 100 and 200 MHz. The
system used an internal comparison-switching scheme to reduce non-smooth
instrumental contaminants in the measured spectrum to 75 mK. From the
observations, we place an initial upper limit of 450 mK on the relative
brightness temperature of the redshifted 21 cm contribution to the spectrum due
to neutral hydrogen in the intergalactic medium (IGM) during the epoch of
reionization, assuming a rapid transition to a fully ionized IGM at a redshift
of 8. With refinement, this technique should be able to distinguish between
slow and fast reionization scenarios. To constrain the duration of reionization
to dz > 2, the systematic residuals in the measured spectrum must be reduced to
3 mK.Comment: Submitted to ApJ. 9 pages including 6 figure
An Improved Method for 21cm Foreground Removal
21-cm tomography is expected to be difficult in part because of serious foreground contamination. Previous studies have found that line-of-sight approaches are capable of cleaning foregrounds to an acceptable level on large spatial scales, but not on small spatial scales. In this paper, we introduce a Fourier space formalism for describing the line-of-sight methods, and use it to introduce an improved new method for 21-cm foreground cleaning. Heuristically, this method involves fitting foregrounds in Fourier space using weighted polynomial fits, with each pixel weighted according to its information content. We show that the new method reproduces the old one on large angular scales, and gives marked improvements on small scales at essentially no extra computational cost.National Science Foundation (U.S.) (Grant AST-0134999)National Science Foundation (U.S.) (Grant AST-05-06556)David & Lucile Packard FoundationResearch Corporatio
A Search for Radio Gravitational Lenses, Using the Sloan Digital Sky Survey and the Very Large Array
We report on a novel search for radio gravitational lenses. Using the Very
Large Array, we imaged ten candidates with both dual redshifts in Sloan Digital
Sky Survey spectra and 1.4 GHz radio flux >2 mJy in the FIRST survey. The VLA
maps show that in each case the radio emission is associated with the
foreground galaxy rather than being lensed emission from the background galaxy,
although at least four of our targets are strong lenses at optical wavelengths.
These SDSS dual-redshift systems do not have lensed radio emission at the
sensitivity of current radio surveys.Comment: 7 pages, 10 figures, uses emulateapj. Accepted to ApJ (11/25/2005).
v2: Minor changes in accepted versio
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