Measuring the Redshift of Reionization with a Modest Array of Low-Frequency Dipoles

The designs of the first generation of cosmological 21-cm observatories are split between single dipole experiments which integrate over a large patch of sky in order to find the global (spectral) signature of reionization, and interferometers with arcminute-scale angular resolution whose goal is to measure the 3D power spectrum of ionized regions during reionization. We examine whether intermediate scale instruments with complete Fourier (uv) coverage are capable of placing new constraints on reionization. We find that even without using a full power spectrum analysis, the global redshift of reionization, z_reion, can in principle be measured from the variance in the 21-cm signal among multiple beams as a function of frequency at a roughly 1 degree angular scale. At this scale, the beam-to-beam variance in the differential brightness temperature peaks when the average neutral fraction was around 50%, providing a convenient flag of z_reion. We choose a low angular resolution of order 1 degree to exploit the physical size of the ionized regions and maximize the signal-to-noise ratio. Thermal noise, foregrounds, and instrumental effects should also be manageable at this angular scale, as long as the uv coverage is complete within the compact core required for low-resolution imaging. For example, we find that z_reion can potentially be detected to within a redshift uncertainty of less than around 1 in around 500 hours of integration on the existing MWA prototype (with only 32x16 dipoles), operating at an angular resolution of around 1 degree and a spectral resolution of 2.4 MHz.Comment: 11 pages, 7 figures. Version published in JCAP (appendix removed, some clarifications and changes to definitions

Implications of the Measured Image Size for the Radio Afterglow of GRB 030329

We use data on the image size of the radio afterglow of GRB 030329 (Taylor et al. 2004) to constrain the physical parameters of this explosion. Together with the observed broad band spectrum, this data over-constrains the physical parameters, thus enabling to test different GRB jet models for consistency. We consider two extreme models for the lateral spreading of the jet: model 1 with relativistic expansion in the local rest frame, and model 2 with little lateral expansion as long as the jet is highly relativistic. We find that both models are consistent with the data for a uniform external medium, while for a stellar wind environment model 1 is consistent with the data but model 2 is disfavored by the data. Our derivations can be used to place tighter constraints on the dynamics and structure of GRB jets in future afterglows, following a denser monitoring campaign for the temporal evolution of their image size.Comment: 12 pages, 6 figues; submitted to Ap

Counts and Sizes of Galaxies in the Hubble Deep Field - South: Implications for the Next Generation Space Telescope

Science objectives for the Next Generation Space Telescope (NGST) include a large component of galaxy surveys, both imaging and spectroscopy. The Hubble Deep Field datasets include the deepest observations ever made in the ultraviolet, optical and near infrared, reaching depths comparable to that expected for NGST spectroscopy. We present the source counts, galaxy sizes and isophotal filling factors of the HDF-South images. The observed integrated galaxy counts reach >500 galaxies per square arcminute at AB<30. We extend these counts to faint levels in the infrared using models. The trend previously seen that fainter galaxies are smaller, continues to AB=29 in the high resolution HDF-S STIS image, where galaxies have a typical half-light radius of 0.1 arcseconds. Extensive Monte Carlo simulations show that the small measured sizes are not due to selection effects until >29mag. Using the HDF-S NICMOS image, we show that galaxies are smaller in the near infrared than they are in the optical. We analyze the isophotal filling factor of the HDF-S STIS image, and show that this image is mostly empty sky even at the limits of galaxy detection, a conclusion we expect to hold true for NGST spectroscopy. At the surface brightness limits expected for NGST imaging, however, about a quarter of the sky is occupied by the outer isophotes of AB<30 galaxies. We discuss the implications of these data on several design concepts of the NGST near-infrared spectrograph. We compare the effects of resolution and the confusion limit of various designs, as well as the multiplexing advantages of either multi-object or full-field spectroscopy. We argue that the optimal choice for NGST spectroscopy of high redshift galaxies is a multi-object spectrograph (MOS) with target selection by a micro electro mechanical system (MEMS) device.Comment: 27 pages including 10 figures, accepted for publication in the Astronomical Journal, June 2000, abridged abstrac

Global 21cm signal experiments: a designer's guide

[Abridged] The spatially averaged global spectrum of the redshifted 21cm line has generated much experimental interest, for it is potentially a direct probe of the Epoch of Reionization and the Dark Ages. Since the cosmological signal here has a purely spectral signature, most proposed experiments have little angular sensitivity. This is worrisome because with only spectra, the global 21cm signal can be difficult to distinguish from foregrounds such as Galactic synchrotron radiation, as both are spectrally smooth and the latter is orders of magnitude brighter. We establish a mathematical framework for global signal data analysis in a way that removes foregrounds optimally, complementing spectra with angular information. We explore various experimental design trade-offs, and find that 1) with spectral-only methods, it is impossible to mitigate errors that arise from uncertainties in foreground modeling; 2) foreground contamination can be significantly reduced for experiments with fine angular resolution; 3) most of the statistical significance in a positive detection during the Dark Ages comes from a characteristic high-redshift trough in the 21cm brightness temperature; and 4) Measurement errors decrease more rapidly with integration time for instruments with fine angular resolution. We show that if observations and algorithms are optimized based on these findings, an instrument with a 5 degree beam can achieve highly significant detections (greater than 5-sigma) of even extended (high Delta-z) reionization scenarios after integrating for 500 hrs. This is in contrast to instruments without angular resolution, which cannot detect gradual reionization. Abrupt ionization histories can be detected at the level of 10-100's of sigma. The expected errors are also low during the Dark Ages, with a 25-sigma detection of the expected cosmological signal after only 100 hrs of integration.Comment: 34 pages, 30 figures. Replaced (v2) to match accepted PRD version (minor pedagogical additions to text; methods, results, and conclusions unchanged). Fixed two typos (v3); text, results, conclusions etc. completely unchange

Galaxy Morphology from NICMOS Parallel Imaging

We present high resolution NICMOS images of random fields obtained in parallel to other HST observations. We present galaxy number counts reaching H=24. The H-band galaxy counts show good agreement with the deepest I- and K-band counts obtained from ground-based data. We present the distribution of galaxies with morphological type to H<23. We find relatively fewer irregular galaxies compared to an I-band sample from the Hubble Deep Field, which we attribute to their blue color, rather than to morphological K-corrections. We conclude that the irregulars are intrinsically faint blue galaxies at z<1.Comment: 13 pages, including 4 figures. Accepted for publication in ApJ Letter

Constraining the unexplored period between reionization and the dark ages with observations of the global 21 cm signal

Observations of the frequency dependence of the global brightness temperature of the redshifted 21 cm line of neutral hydrogen may be possible with single dipole experiments. In this paper, we develop a Fisher matrix formalism for calculating the sensitivity of such instruments to the 21 cm signal from reionization and the dark ages. We show that rapid reionization histories with duration delta z< 2 can be constrained, provided that local foregrounds can be well modelled by low order polynomials. It is then shown that observations in the range nu = 50 - 100 MHz can feasibly constrain the Lyman alpha and X-ray emissivity of the first stars forming at z = 15 - 25, provided that systematic temperature residuals can be controlled to less than 1 mK. Finally, we demonstrate the difficulty of detecting the 21 cm signal from the dark ages before star formation.Comment: 11 pages, 14 figures, submitted to PR

A question of faith?:prosecuting religiously aggravated offences in England and Wales

Have some of the prosecutions for religiously aggravated offences going before the courts amounted to attempts to apply unjust prohibitions against freedom of speech? Is there any evidence that the provisions for religiously aggravated offences have been applied to suppress criticism of religion? This paper applies an analysis of Crown Prosecution Service records on religiously aggravated offences to address these questions

Linguistic impoliteness and religiously aggravated hate crime in England and Wales

Despite its centrality to religiously aggravated hate crime recorded in England and Wales, the nature of the language used has been neglected in research. This paper, based on a unique dataset, aims to rectify this. It takes its approach from the field of linguistic impoliteness, a field that has yet to consider hate crime. Therein lies our second aim: to consider whether impoliteness notions can be usefully extended to the language of hate crime. In our data, we examine, in particular, conventionalized impoliteness formulae, insults, threats, incitement and taboo words. Whilst we reveal some linguistic support for the way religiously aggravated hate crime is framed in the law and discussed in the legal literature, we highlight areas of neglect and potential ambiguity. Regarding impoliteness, we demonstrate its effectiveness as an approach to this data, but we also highlight areas of neglect in that literature too, notably, non-conditional threats and incitement

Generic local distinguishability and completely entangled subspaces

A subspace of a multipartite Hilbert space is completely entangled if it contains no product states. Such subspaces can be large with a known maximum size, S, approaching the full dimension of the system, D. We show that almost all subspaces with dimension less than or equal to S are completely entangled, and then use this fact to prove that n random pure quantum states are unambiguously locally distinguishable if and only if n does not exceed D-S. This condition holds for almost all sets of states of all multipartite systems, and reveals something surprising. The criterion is identical for separable and for nonseparable states: entanglement makes no difference.Comment: 12 page

CELLO: A fast algorithm for Covariance Estimation

We present CELLO (Covariance Estimation and Learning through Likelihood Optimization), an algorithm for predicting the covariances of measurements based on any available informative features. This algorithm is intended to improve the accuracy and reliability of on-line state estimation by providing a principled way to extend the conventional fixed-covariance Gaussian measurement model. We show that in experiments, CELLO learns to predict measurement covariances that agree with empirical covariances obtained by manually annotating sensor regimes. We also show that using the learned covariances during filtering provides substantial quantitative improvement to the overall state estimate. © 2013 IEEE.United States. National Aeronautics and Space AdministrationSiemens Corporate ResearchUnited States. Office of Naval Research. Multidisciplinary University Research InitiativeMicro Autonomous Consortium Systems and Technolog