The host galaxies of luminous radio-quiet quasars

We present the results of a deep K -band imaging study which reveals the host galaxies around a sample of luminous radio-quiet quasars. The K -band images, obtained at UKIRT, are of sufficient quality to allow accurate modelling of the underlying host galaxy. Initially, the basic structure of the hosts is revealed using a modified clean deconvolution routine optimized for this analysis. Two of the 14 quasars are shown to have host galaxies with violently disturbed morphologies which cannot be modelled by smooth elliptical profiles. For the remainder of our sample, 2D models of the host and nuclear component are fitted to the images using the χ ² statistic to determine goodness of fit. Host galaxies are detected around all of the quasars. The reliability of the modelling is extensively tested, and we find the host luminosity to be well constrained for nine quasars. The derived average K -band absolute K -corrected host galaxy magnitude for these luminous radio-quiet quasars is 〈 M _K 〉=25.15±0.04, slightly more luminous than an L * galaxy. The spread of derived host galaxy luminosities is small, although the spread of nuclear-to-host ratios is not. These host luminosities are shown to be comparable to those derived from samples of quasars of lower total luminosity, and we conclude that there is no correlation between host and nuclear luminosity for these quasars. Nuclear-to-host ratios break the lower limit previously suggested from studies of lower nuclear luminosity quasars and Seyfert galaxies. Morphologies are less certain but, on the scales probed by these images, some hosts appear to be dominated by spheroids while others appear to have disc-dominated profiles.     

Bayesian galaxy shape measurement for weak lensing surveys – I. Methodology and a fast-fitting algorithm

The principles of measuring the shapes of galaxies by a model-fitting approach are discussed in the context of shape measurement for surveys of weak gravitational lensing. It is argued that such an approach should be optimal, allowing measurement with maximal signal-to-noise ratio, coupled with estimation of measurement errors. The distinction between likelihood-based and Bayesian methods is discussed. Systematic biases in the Bayesian method may be evaluated as part of the fitting process, and overall such an approach should yield unbiased shear estimation without requiring external calibration from simulations. The principal disadvantage of model fitting for large surveys is the computational time required, but here an algorithm is presented that enables large surveys to be analysed in feasible computation times. The method and algorithm is tested on simulated galaxies from the Shear TEsting Programme (STEP).     

Australites from Northern Australia

Abstract— Abundant tektites have been found in buried alluvial gravels at the south end of Lake Argyle in far northern Australia. The recovered tektites are unusual in that an astounding number are very large and 75% of those analyzed to date are HMg tektites, heretofore a very rare type in Australia. It is now clear that the paucity of tektites in northern Australia is due to the former high energy erosional environment rather than to crossing the strewnfield boundary, as has been previously suggested. The N-S extent of the australite strewnfield encompasses the entire continent.     

An early Holocene oxygen isotope record from the Olson buried forest bed, Southern Lake Michigan

Analysis of a 3.5 m vibracore from the Olson buried forest bed in the southern Lake Michigan basin provides new paleolimnological data for the early Holocene. The core records a rise in lake level from the Chippewa low water phase toward the Nipissing high water phase. Deepening of the water level at the core site is suggested by a trend toward decreasing organic carbon content up core that is interpreted as a response to increasing distance between terrestrial debris sources and the core site.Published data from deep water cores from the southern Lake Michigan basin suggest there had been an inflow of isotopically light water from glacial Lake Agassiz into the southern basin between 10.5-11 ka (A1 event). The data also indicate a second flood of isotopically light water between 8-9 ka (A2 event).Three new ¹⁴C dates from the Olson site core suggest that most of the sediment was deposited between 8.45 ka and 8.2 ka, an interval roughly coeval with the second pulse of ¹⁸O-depleted water (A2) from Lake Agassiz into the southern basin. Oxygen isotope ratio analysis of shell aragonite from the gastropods Probythinella lacustris and Marstonia deceptashows increasingly negative values up core. This trend in¹⁸O values suggests that ¹⁸O - depleted water entered the southern basin about 8.4 ka. The Olson site core thus provides a chronology of events in the southern Lake Michigan basin associated with the draining of glacial Lake Agassiz.     

Millisecond-duration microwave burst observations with the SSRT fast data acquisition system

The hardware and software for the observation of millisecond bursts with the Siberian solar radio telescope (SSRT) at 5.2 cm is described. The multiprocessing computer and data acquisition system records 180 analog signals from the SSRT multichannel receiver every 7 milliseconds. The recorded information opens the opportunity to study the position, structure, and other characteristics of solar burst sources with high temporal and spatial resolution. Examples of the observations are presented and briefly discussed in order to illustrate the overall performance of the system.     

Bright photospheric areas surrounding sunspot groups at 5700 Å

Sunspot groups at various central angles were chosen to study what appears to be an enhanced surrounding area, even at small central angles. The continuous band of observation was 200 Å wide, centered at 5700 Å. The enhancement has been seen before, but only at higher frequencies, as by Jayanthan in the ultraviolet. Four years of sunspot pictures from March 1957 to March 1961, were inspected and no instance of the non-appearance of the enbancement was noted. An attempt to show proof was made by photometry and by high contrast prints of the areas around groups at different central angles. It was shown that more than half of the flux deficit reappears in this enhancement.