Spectroscopy of the optical Einstein ring 0047-2808

We present optical and near-infrared spectroscopic observations of the optical Einstein ring 0047-2808. We detect both [OIII] lines 4959, 5007 near 2.3 micron, confirming the redshift of the lensed source as z=3.595. The Ly-a line is redshifted relative to the [OIII] line by 140+-20 km/s. Similar velocity shifts have been seen in nearby starburst galaxies. The [OIII] line is very narrow, 130 km/s FWHM. If the ring is the image of the centre of a galaxy the one-dimensional stellar velocity dispersion sigma=55 km/s is considerably smaller than the value predicted by Baugh et al. (1998) for the somewhat brighter Lyman-break galaxies. The Ly-a line is significantly broader than the [OIII] line, probably due to resonant scattering. The stellar central velocity dispersion of the early-type deflector galaxy at z=0.485 is 250+-30 km/s. This value is in good agreement both with the value predicted from the radius of the Einstein ring (and a singular isothermal sphere model for the deflector), and the value estimated from the D_n-sigma relation.Comment: 7 pages, 3 figures, accepted for publication in MNRA

Thermal and electronic transport properties of zinc antimonide scientific report no. 1

Single crystals of p-type zinc antimonide - thermal and electronic transport propertie

Redshifted 21cm Signatures Around the Highest Redshift Quasars

The Ly-alpha absorption spectrum of the highest redshift quasars indicates that they are surrounded by giant HII regions, a few Mpc in size. The neutral gas around these HII regions should emit 21cm radiation in excess of the Cosmic Microwave Background, and enable future radio telescopes to measure the transverse extent of these HII regions. At early times, the HII regions expand with a relativistic speed. Consequently, their measured sizes along the line-of-sight (via Ly-alpha absorption) and transverse to it (via 21 cm emission) should have different observed values due to relativistic time-delay. We show that the combined measurement of these sizes would directly constrain the neutral fraction of the surrounding intergalactic medium (IGM) as well as the quasar lifetime. Based on current number counts of luminous quasars at z>6, an instrument like LOFAR should detect >2 redshifted 21cm shells per field (with a radius of 11 degrees) around active quasars as bright as those already discovered by SDSS, and >200 relic shells of inactive quasars per field. We show that Ly-alpha photons from the quasar are unable to heat the IGM or to couple the spin and kinetic temperatures of atomic hydrogen beyond the edge of the HII region. The detection of the IGM in 21cm emission around high redshift quasars would therefore gauge the presence of a cosmic Ly-alpha background during the reionization epoch.Comment: 11 pages, 6 figures. Submitted to Ap

Scattered Lyman-alpha Radiation Around Sources Before Cosmological Reionization

The spectra of the first galaxies and quasars in the Universe should be strongly absorbed shortward of their rest-frame Lyman-alpha wavelength by neutral hydrogen (HI) in the intervening intergalactic medium. However, the Lyman-alpha line photons emitted by these sources are not eliminated but rather scatter until they redshift out of resonance and escape due to the Hubble expansion of the surrounding intergalactic HI. We calculate the resulting brightness distribution and the spectral shape of the diffuse Lyman-alpha line emission around high redshift sources, before the intergalactic medium was reionized. Typically, the Lyman-alpha photons emitted by a source at z=10 scatter over a characteristic angular radius of order 15 arcseconds around the source and compose a line which is broadened and redshifted by about a thousand km/s relative to the source. The scattered photons are highly polarized. Detection of the diffuse Lyman-alpha halos around high redshift sources would provide a unique tool for probing the neutral intergalactic medium before the epoch of reionization. On sufficiently large scales where the Hubble flow is smooth and the gas is neutral, the Lyman-alpha brightness distribution can be used to determine the cosmological mass densities of baryons and matter.Comment: 21 pages, 5 Postscript figures, accepted by ApJ; figures 1--3 corrected; new section added on the detectability of Lyman alpha halos; conclusions update

Cosmic 21-cm Delensing of Microwave Background Polarization and the Minimum Detectable Energy Scale of Inflation

The curl (B) modes of cosmic microwave background (CMB) polarization anisotropies are a unique probe of the primordial background of inflationary gravitational waves (IGWs). Unfortunately, the B-mode polarization anisotropies generated by gravitational waves at recombination are confused with those generated by the mixing of gradient-mode (E-mode) and B-mode polarization anisotropies as CMB photons propagate through the Universe and are gravitationally lensed. We describe here a method for delensing CMB polarization anisotropies using observations of anisotropies in the cosmic 21-cm radiation emitted or absorbed by neutral hydrogen atoms at redshifts 10 to 200. While the detection of cosmic 21-cm anisotropies at high resolution is challenging, a combined study with a relatively low-resolution (but high-sensitivity) CMB polarization experiment could probe inflationary energy scales well below the Grand Unified Theory (GUT) scale of 10^{16} GeV -- constraining models with energy scales below 10^{15} GeV (the detectable limit derived from CMB observations alone). The ultimate theoretical limit to the detectable inflationary energy scale via this method may be as low as 3 \times 10^{14} GeV.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let

Aliphatic polyester polymer stars: synthesis, properties and applications in biomedicine and nanotechnology

abstract: A critical review: the ring-opening polymerization of cyclic esters provides access to an array of biodegradable, bioassimilable and renewable polymeric materials. Building these aliphatic polyester polymers into larger macromolecular frameworks provides further control over polymer characteristics and opens up unique applications. Polymer stars, where multiple arms radiate from a single core molecule, have found particular utility in the areas of drug delivery and nanotechnology. A challenge in this field is in understanding the impact of altering synthetic variables on polymer properties. We review the synthesis and characterization of aliphatic polyester polymer stars, focusing on polymers originating from lactide, epsilon-caprolactone, glycolide, beta-butyrolactone and trimethylene carbonate monomers and their copolymers including coverage of polyester miktoarm star copolymers. These macromolecular materials are further categorized by core molecules, catalysts employed, self-assembly and degradation properties and the resulting fields of application (262 references)

Prospects for Redshifted 21-cm observations of quasar HII regions

The introduction of low-frequency radio arrays over the coming decade is expected to revolutionize the study of the reionization epoch. Observation of the contrast in redshifted 21cm emission between a large HII region and the surrounding neutral IGM will be the simplest and most easily interpreted signature. We find that an instrument like the planned Mileura Widefield Array Low-Frequency Demonstrator (LFD) will be able to obtain good signal to noise on HII regions around the most luminous quasars, and determine some gross geometric properties, e.g. whether the HII region is spherical or conical. A hypothetical follow-up instrument with 10 times the collecting area of the LFD (MWA-5000) will be capable of mapping the detailed geometry of HII regions, while SKA will be capable of detecting very narrow spectral features as well as the sharpness of the HII region boundary. The MWA-5000 will discover serendipitous HII regions in widefield observations. We estimate the number of HII regions which are expected to be generated by quasars. Assuming a late reionization at z~6 we find that there should be several tens of quasar HII regions larger than 4Mpc at z~6-8 per field of view. Identification of HII regions in forthcoming 21cm surveys can guide a search for bright galaxies in the middle of these regions. Most of the discovered galaxies would be the massive hosts of dormant quasars that left behind fossil HII cavities that persisted long after the quasar emission ended, owing to the long recombination time of intergalactic hydrogen. A snap-shot survey of candidate HII regions selected in redshifted 21cm image cubes may prove to be the most efficient method for finding very high redshift quasars and galaxies.Comment: 14 pages, 8 figures. Submitted to Ap

Issues for the Next Generation of Galaxy Surveys

I argue that the weight of the available evidence favours the conclusions that galaxies are unbiased tracers of mass, the mean mass density (excluding a cosmological constant or its equivalent) is less than the critical Einstein-de Sitter value, and an isocurvature model for structure formation offers a viable and arguably attractive model for the early assembly of galaxies. If valid these conclusions complicate our work of adding structure formation to the standard model for cosmology, but it seems sensible to pay attention to evidence.Comment: 14 pages, 3 postscript figures, uses rspublic.st