Gary M. Bernstein

Detection of lens candidates for the double QSO Q2245+007

Luminous objects associated with the 7.06″ separation double quasar Q2345+007 have, until now, escaped detection. In this letter we present the results of the deepest known imaging of the region surrounding the quasar. The total exposure times were 47600 seconds in Bj (101 frames) and 32160 seconds in R (82 frames). The frames came from CFHT, CTIO, and KPNO. We detect a Bj=25.0 mag galaxy (Bj−R=0.5 mag) in close proximity to the fainter QSO image, possibly at z=1.49 given by several absorption features in the QSO spectra. Furthermore, there is a 2.9σ enhancement in the number density of faint galaxies (24≤Bj≤28, Bj−R≤1.5) near the quasar and another 3.1σ enhancement further away. These discoveries support the hypothesis that Q2345+007 is being lensed by one or more distant mass concentrations and may imply that compact ‘‘clusters’’ already exist at early epochs. We discuss several lens models for the system and the cosmological implications.

THE NEAR-INFRARED TULLY-FISHER RELATION: A PRELIMINARY STUDY OF THE COMA AND ABELL 400 CLUSTERS

We have started a large project to study the near-infrared luminosity-linewidth (Tully-Fisher) relation using H- and I-band surface photometry of spiral galaxies. A preliminary study of 20 spirals in the Coma and Abell 400 clusters (both at ~7000 km s-1) is presented. The near-infrared images have been used to derive accurate inclinations and total magnitudes, and rotational line widths are measured from high quality 21 cm Arecibo data. The scatter in the Coma Tully-Fisher plot is found to be 0.19 mag in the H-band and 0.20 mag in the I-band for a set of 13 galaxies, if we assume that they are all at the same distance. The deviation of the Coma galaxies from the best-fit Tully-Fisher relation is correlated with their redshift, indicating that some of the galaxies are not bound to the cluster. Indeed, if we treat all the galaxies in the Coma sample as undergoing free Hubble expansion, the Tully-Fisher scatter drops to 0.12 mag and 0.13 mag for the H- and I-band datasets, respectively. The Abell 400 sample is best fit by a common distance model, yielding a scatter of 0.12 mag for seven galaxies in H using a fixed Tully-Fishr slope (derived from our Coma H sample). We are in the process of studying cluster and field spirals out to ~10,000 km s-1 in order to calibrate the near-infrared Tully-Fisher relation and will apply it to more nearby galaxies to measure the peculiar velocity field (and hence the mass distribution) in the local Universe.

Gravitational lensing of quasar 0957+561 and the determination of H0

The double quasar 0957+561 was the first discovered instance of multiple imaging via gravitational lensing. The galaxy cluster is an important deflector as well as the first ranked galaxy. This has so far precluded construction of a unique model of the lens, reducing the accuracy of the derived H0 value. We have obtained deep images of the system at CFHT. The cluster is sufficiently massive to cause distortions on distant background galaxy images. We have used a mass map derived from lensing distortions to improve the accuracy of the cluster center location and place new limits on H0.