Gravitational lensing by elliptical galaxies

The fraction of high-redshift sources which are multiply-imaged by intervening galaxies is strongly dependent on the cosmological constant, and so can be a useful probe of the cosmological model. However its power is limited by various systematic (and random) uncertainties in the calculation of lensing probabilities, one of the most important of which is the dynamical normalisation of elliptical galaxies. Assuming ellipticals' mass distributions can be modelled as isothermal spheres, the mass normalisation depends on: the velocity anisotropy; the luminosity density; the core radius; and the area over which the velocity dispersion is measured. The differences in the lensing probability and optical depth produced by using the correct normalisation can be comparable to the differences between even the most extreme cosmological models. The existing data is not sufficient to determine the correct normalisation with enough certainty to allow lensing statistics to be used to their full potential. However, as the correct lensing probability is almost certainly higher than is usually assumed, upper bounds on the cosmological constant are not weakened by these possibilities.Comment: MNRAS, in press; 13 pages, 22 figure

Gravitational lensing in galaxy redshift surveys

Gravitationally-lensed quasars should be discovered as a by-product of large galaxy redshift surveys, being discovered spectroscopically when a low-redshift galaxy exhibits high-redshift quasar emission lines. The number of lenses expected is higher than previously estimated, mainly due to the fact that the presence of the quasar images brings faint deflector galaxies above the survey limit. Thus the a posteriori likelihood of the discovery of Q 2237+0305 in the Center for Astrophysics redshift survey is approximately 0.03. In the future, the 2 degree Field survey should yield at least 10 lensed quasars, and the Sloan Digitial Sky Survey up to 100.Comment: Gravitational Lensing: Recent Progress and Future Goals, C.S. Kochanek & T.G. Brainerd, eds., in press; 2 pages, 1 figur

Using the 2dF galaxy redshift survey to detect gravitationally-lensed quasars

Galaxy redshift surveys can be used to detect gravitationally-lensed quasars if the spectra obtained are searched for the quasars' emission lines. Previous investigations of this possibility have used simple models to show that the 2 degree Field (2dF) redshift survey could yield several tens of new lenses, and that the larger Sloan Digital Sky Survey should contain an order of magnitude more. However the particular selection effects of the samples were not included in these calculations, limiting the robustness of the predictions; thus a more detailed simulation of the 2dF survey was undertaken here. The use of an isophotal magnitude limit reduces both the depth of the sample and the expected number of lenses, but more important is the Automatic Plate Measuring survey's star-galaxy separation algorithm, used to generate the 2dF input catalogue. It is found that most quasar lenses are classed as merged stars, with only the few lenses with low-redshift deflectors likely to be classified as galaxies. Explicit inclusion of these selection effects implies that the 2dF survey should contain 10 lenses on average. The largest remaining uncertainty is the lack of knowledge of the ease with which any underlying quasars can be extracted from the survey spectra.Comment: MNRAS, in press; 14 pages, 19 figure

A SURVEY FOR ODONTOCETE CETACEANS OFF KAUA‘I AND NI‘IHAU, HAWAI‘I, DURING OCTOBER AND NOVEMBER 2005: EVIDENCE FOR POPULATION STRUCTURE AND SITE FIDELITY

Considerable uncertainty exists regarding population structure and population sizes of most species of odontocetes in the Hawaiian Islands. A small-boat based survey for odontocetes was undertaken off the islands of Kaua‘i and Ni‘ihau in October and November 2005 to photoidentify individuals and collect genetic samples for examining stock structure. Field effort on 24 days covered 2,194 km of trackline. Survey coverage was from shallow coastal waters out to over 3,000 m depth, though almost half (47%) was in waters less than 500 m in depth. There were 56 sightings of five species of odontocetes: spinner dolphins (30 sightings); bottlenose dolphins (14 sightings); short-finned pilot whales (6 sightings); rough-toothed dolphins (5 sightings); and pantropical spotted dolphins (1 sighting). One hundred and five biopsy samples were collected and 14,960 photographs were taken to document morphology and for individual photo-identification. Photographs of distinctive individuals of three species (bottlenose dolphins, 76 identifications; rough-toothed dolphins, 157 identifications; short-finned pilot whales, 68 identifications) were compared to catalogs of these species from a survey off Kaua‘i and Ni‘ihau in 2003, as well as from efforts off O‘ahu, Maui/Lana‘i and the island of Hawai‘i. Within- and between-year matches were found for all three species with individuals previously identified off Kaua‘i and Ni‘ihau, though no matches were found with individuals off any of the other islands. This suggests site fidelity to specific island areas, and population structure among island areas for all three species. Movements of photographically identified bottlenose dolphins were documented between deep water areas off the islands of Kaua‘i and Ni‘ihau, as well as between shallow (\u3c350 m) and deep (\u3e350 m) waters. A lack of sightings or reports of false killer whales off Kaua‘i or Ni‘ihau during our study, combined with documented movements among the other main Hawaiian Islands, suggest that there is no “resident” population of false killer whales that inhabits waters only off Kaua‘i or Ni‘iha

The Ray Bundle method for calculating weak magnification by gravitational lenses

We present here an alternative method for calculating magnifications in gravitational lensing calculations -- the Ray Bundle method. We provide a detailed comparison between the distribution of magnifications obtained compared with analytic results and conventional ray-shooting methods. The Ray Bundle method provides high accuracy in the weak lensing limit, and is computationally much faster than (non-hierarchical) ray shooting methods to a comparable accuracy. The Ray Bundle method is a powerful and efficient technique with which to study gravitational lensing within realistic cosmological models, particularly in the weak lensing limit.Comment: 9 pages Latex, 8 figures, submitted to MNRA

Kinematics and Mass Profile of AWM 7

We have measured 492 redshifts (311 new) in the direction of the poor cluster AWM~7 and have identified 179 cluster members (73 new). We use two independent methods to derive a self-consistent mass profile, under the assumptions that the absorption-line galaxies are virialized and that they trace an underlying Navarro, Frenk & White (1997) dark matter profile: (1) we fit such an NFW profile to the radial distribution of galaxy positions and to the velocity dispersion profile; (2) we apply the virial mass estimator to the cluster. With these assumptions, the two independent mass estimates agree to \sim 15% within 1.7 h^{-1} Mpc, the radial extent of our data; we find an enclosed mass \sim (3+-0.5)\times 10^{14} h^{-1} M_\odot. The largest potential source of systematic error is the inclusion of young emission-line galaxies in the mass estimate. We investigate the behavior of the surface term correction to the virial mass estimator under several assumptions about the velocity anisotropy profile, still within the context of the NFW model, and remark on the sensitivity of derived mass profiles to outliers. We find that one must have data out to a large radius in order to determine the mass robustly, and that the surface term correction is unreliable at small radii.Comment: LaTeX, 5 tables, 7 figures, appeared as 2000 AJ 119 44; typos and Eq. 9 corrected; results are unaffecte

Movements and spatial use of odontocetes in the western main Hawaiian Islands: results from satellite-tagging and photo-identification off Kaua‘i and Ni‘ihau in July/August 2011

Although considerable information is available on residency patterns and spatial use of odontocetes in the eastern half of the Hawai‘i Range Complex (HRC), much less is known about odontocetes in the western half of the HRC. In the second year of a three-year effort in the western main Hawaiian Islands we undertook surveys off Kaua‘i and Ni‘ihau in July/August 2011, to examine spatial use and residency patterns using satellite tags, to provide visual verification of acoustically-detected odontocetes on the Pacific Missile Range Facility (PMRF), and to obtain individual identification photographs and biopsy samples for assessment of population identity and structure. During 18 days of field effort we covered 1,972 km of trackline and had 65 encounters with five species of odontocetes. Twenty-four of the encounters, of three species, were cued by acoustic detections from the Marine Mammal Monitoring on Navy Ranges (M3R) system, thus providing species verifications for future use of the M3R system on the PMRF range. During the 65 encounters we obtained 22,645 photos for individual and species identification, and collected 48 biopsy samples for genetic analyses. One encounter with a group of four killer whales was only the second encounter with this species in 12 years of directed field surveys in Hawaiian waters. Photos from that encounter were compared to our photo-identification catalog but no matches were found, further suggesting that there is no population of this species resident to the Hawaiian Islands. There were three encounters with a lone pantropical spotted dolphin, each time in association with a group of spinner dolphins. Photos of this individual matched to a spotted dolphin identified off Kaua‘i in 2004 and in 2005, both times with spinner dolphins, suggesting this individual may be part of a long-term association with spinner dolphins. Four satellite tags were deployed; three on rough-toothed dolphins and one on a bottlenose dolphin. These are the first tag deployments on either species in Hawaiian waters and the first deployments of satellite tags on free-ranging rough-toothed dolphins anywhere in the world. Rough-toothed dolphin tag data were obtained over periods from 7.6 to 18.5 days. Over these periods the three rough-toothed dolphins moved cumulative horizontal distances ranging from 573 to 1,295 km, yet remained an average distance from the tagging locations of from 10.4 to 13.9 km. Median depths used by the three rough-toothed dolphins ranged from 816 to 1,107 m, with median distance from shore ranging from 11.6 to 12.2 km. Two of the three individuals had been previously photo-identified off Kaua‘i (in 2007 or 2008), and all link by association with the resident population from Kaua‘i and Ni‘ihau. Movement and habitat use data were obtained over a 34-day period for the satellite-tagged bottlenose dolphin. During this time the individual remained associated with the island of Kaua‘i using waters with a median depth of 82 m. Although this individual had not been previously photo-identified, others from the group it was in had been previously documented off Kaua‘i and/or Ni‘ihau in 2003-2005, suggesting it is part of the island-resident population. Overall these efforts provide the first unbiased movement and habitat use data for both species in Hawaiian waters.Grant No. N00244-10-1-004