arXiv subjects

Cathryn M. Trott

Publications and source records attributed to Cathryn M. Trott.

58 records · Page 4Linked to original sources

arXiv2012

The impact of point source subtraction residuals on 21 cm Epoch of Reionization estimation

Precise subtraction of foreground sources is crucial for detecting and estimating 21cm HI signals from the Epoch of Reionization (EoR). We quantify how imperfect point source subtraction due to limitations of the measurement dataset yields structured residual signal in the dataset. We use the Cramer-Rao lower bound, as a metric for quantifying the precision with which a parameter may be measured, to estimate the residual signal in a visibility dataset due to imperfect point source subtraction. We then propagate these residuals into two metrics of interest for 21cm EoR experiments - the angular and two-dimensional power spectrum - using a combination of full analytic covariant derivation, analytic variant derivation, and covariant Monte Carlo simulations. This methodology differs from previous work in two ways: (1) it uses information theory to set the point source position error, rather than assuming a global root-mean-square error, and (2) it describes a method for propagating the errors analytically, thereby obtaining the full correlation structure of the power spectra. The methods are applied to two upcoming low-frequency instruments: the Murchison Widefield Array and the Precision Array for Probing the Epoch of Reionization. In addition to the actual antenna configurations, we apply the methods to minimally-redundant and maximally-redundant configurations. We find that for peeling sources above 1 Jy, the amplitude of the residual signal, and its variance, will be smaller than the contribution from thermal noise for the observing parameters proposed for upcoming EoR experiments, and that optimal subtraction of bright point sources will not be a limiting factor for EoR parameter estimation. We then use the formalism to provide an ab initio analytic derivation motivating the 'wedge' feature in the two-dimensional power spectrum, complementing previous discussion in the literature.

astro-ph.CO↗

arXiv2011

Source detection in interferometric visibility data. I. Fundamental estimation limits

Transient radio signals of astrophysical origin present an avenue for studying the dynamic universe. With the next generation of radio interferometers being planned and built, there is great potential for detecting and studying large samples of radio transients. Currently-used image-based techniques for detecting radio sources have not been demonstrated to be optimal, and there is a need for development of more sophisticated algorithms, and methodology for comparing different detection techniques. A visibility-space detector benefits from our good understanding of visibility-space noise properties, and does not suffer from the image artifacts and need for deconvolution in image-space detectors. In this paper, we propose a method for designing optimal source detectors using visibility data, building on statistical decision theory. The approach is substantially different to conventional radio astronomy source detection. Optimal detection requires an accurate model for the data, and we present a realistic model for the likelihood function of radio interferometric data, including the effects of calibration, signal confusion and atmospheric phase fluctuations. As part of this process, we derive fundamental limits on the calibration of an interferometric array, including the case where many relatively weak "in-beam" calibrators are used. These limits are then applied, along with a model for atmospheric phase fluctuations, to determine the limits on measuring source position, flux density and spectral index, in the general case. We then present an optimal visibility-space detector using realistic models for an interferometer.

astro-ph.IM↗

arXiv2004

Collapsed and Extended Cold Dark Matter Haloes in Softened N-Body Gravity

The statistical mechanics of N cold dark matter (CDM) particles interacting via a softened gravitational potential is reviewed in the microcanonical ensemble and mean-field limit. A phase diagram for the system is computed as a function of the total energy E and gravitational softening length epsilon. For softened systems, two stable phases exist: a collapsed phase, whose radial density profile rho(r) is a central Dirac cusp, and an extended phase, for which rho(r) has a central core and rho(r) ~ r^{-2.2} at large r. It is shown that many N-body simulations of CDM haloes in the literature inadvertently sample the collapsed phase only, even though this phase is unstable when there is zero softening. Consequently, there is no immediate reason to expect agreement between simulated and observed profiles unless the gravitational potential is appreciably softened in nature.

astro-ph↗

arXiv2002

Dissecting a galaxy: mass distribution of 2237+0305

We determine the mass distribution of a spiral galaxy, 2237+0305 using both gravitational lensing and dynamical constraints. We find that lensing can break the disc-halo degeneracy. 2237+0305 has a sub-maximal disc, contributing 57+/-3 per cent of the rotational support at the disc maximum. The disc mass-to-light ratio is 1.1+/-0.2 in the I-band and the bulge, 2.9+/-0.5. The dark matter halo, modelled as a softened isothermal sphere, has a large core radius (13.4+/-0.4 kpc, equivalent to 1.4r_d) to high accuracy for the best-fitting solution. The image positions are reasonably well fitted, but require further rotation information to obtain a unique solution.

astro-ph↗