arXiv subjects

Wesley N. Colley

Publications and source records attributed to Wesley N. Colley.

21 records · Page 2Linked to original sources

arXiv1995

The Evolution of Viscous Inclined Disks in Axisymmetric and Triaxial Galaxies

We have used a set of equations developed by Pringle (1992) to follow the evolution of a viscous twisted disk in a galaxy-like potential which is stationary or tumbling relative to inertial space. In an axisymmetric potential, the disk settles to the equatorial plane at a rate determined largely by the coefficient $ν_2$ associated with shear perpendicular to the local disk plane. If the disk is initially close to the galaxy equator, the rate at which the inclination decays is well described by the analytic formula of Steiman-Cameron and Durisen (1988); in a highly inclined disk, `breaking waves' of curvature steepen as they propagate through the disk, rendering the numerical treatment untrustworthy. In a triaxial potential which is stationary in inertial space, settling is faster than in an oblate or prolate galaxy, since the disk twists simultaneously about two perpendicular axes. If the figure of the potential tumbles about one of its principal axes, the viscous disk can settle into a warped state in which gas at each radius follows a stable tilted orbit which precesses so as to remain stationary relative to the underlying galaxy.

astro-ph↗

arXiv1995

Unlensing Multiple Arcs in 0024+1654: Reconstruction of the Source Image

A unique reconstruction of the image of a high redshift source galaxy responsible for multiple long arcs in the z = 0.4 cluster 0024+1654 is obtained by inverse lensing. Deep B and I imaging with the Hubble Space Telescope (Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, under NASA contract NAS 5-26555) enables high resolution of the arcs due to strong gravitational lensing of the background source. The gravitational lens in the foreground cluster is thus used to obtain a magnified view of the distant source. Four strongly lensed images of the source lead to a unique reconstruction. Each of the long arcs, when unlensed, leads to the same reconstructed source image exhibiting a beaded ring-like morphology. The U luminosity of the ring alone is equivalent to a normal galaxy. This is likely a galaxy in formation.

astro-ph↗

arXiv1994

Observational Prospects for Extra-Galactic Microlensing Events

We consider the feasibility of directly observing gravitational microlensing in extra-galactic sources, whose stars are not generally resolved. This precludes use of the simple optical depth to microlensing formulation, which is applicable only to resolved stars. We, instead, extend this method to consider observational constraints, such as seeing, sky background and minimum detectable change in magnitude. Our analysis provides quantitative relations between these constraints and the expected observational results, event duration and number of detections per year. We find that an ambitious ground-based observer should detect several events per year in M31. We also consider detection of microlensing in visual binary galaxies. We find that, although these objects may present hundreds of events per year, extremely short durations would yield poor prospects for observation.

astro-ph↗