Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We describe different methods for estimating the bispectrum of Cosmic Microwave Background data. In particular we construct a minimum variance estimator for the flat-sky limit and compare results with previously-studied frequentist methods. Application to the MAXIMA dataset shows consistency with primordial Gaussianity. Weak quadratic non-Gaussianity is characterised by a tunable parameter $f_{NL}$, corresponding to non-Gaussianity at a level $\sim 10^{-5}f_{NL}$ (ratio of non-Gaussian to Gaussian terms), and we find limits of $|f_{NL}|<950$ for the minimum-variance estimator and $|f_{NL}|<1650$ for the usual frequentist estimator. These are the tightest limits on primordial non-Gaussianity which include the full effects of the radiation transfer function.

Abstract:

We report the possible discovery of multiple gravitationally-lensed images of QSOs with angular separations on arcminute scales. The QSOs were selected from the completed 2dF QSO survey as having redshifts and optical colours which are statistically consistent. In this paper we present higher-quality optical spectra of the candidates and discuss the likelihood of their genuinely being systems lensed by massive clusters of galaxies. From a comparison of the spectra it appears that up to six pairs of QSOs may be lensed multiple images, although the true number may be less than that and further observations should be undertaken to amass more evidence and to detect the lensing clusters. Two of the candidates may be associated with low redshift clusters of galaxies.

Abstract:

We report the spectroscopic identification of close to 1000 hydrogen-rich (DA) white dwarfs discovered in the course of the Anglo-Australian 2dF QSO Redshift Survey (2QZ). We measured the atmospheric parameters of a subsample of 201 stars based on good-quality Balmer line spectra and we determine the 2QZ population characteristics. Over ten per cent of the sample are potential ZZ Ceti variables. We estimate the DA white dwarf birthrate (bDA = 0.5-1.0 × 10^-12 yr^-1 pc^-3) and the scaleheight (h = 220-300 pc) of the population in the thin disc of the Galaxy by combining information acquired in the Palomar-Green, AAT-UVX and new 2QZ surveys. White dwarfs appear related to G and late-F progenitors. A catalogue of 201 DA white dwarfs is presented.