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A Measurement of the Cosmological Constant Using Elliptical Galaxies as Strong Gravitational Lenses
Myungshin Im, Richard E. Griffiths, Kavan U. Ratnatunga
We have identified seven (field) elliptical galaxies acting as strong gravitational lenses and have used them to measure cosmological parameters. To find the most likely value for…
Evidence for Galaxy Interactions/Mergers from Meduim-Deep Survey WFPC2 Data
L. W. Neuschaefer, M. Im, K. U. Ratnatunga +2
We examine the morphological and statistical properties of close galaxy pairs from two sets of 28 WFPC2 fields, acquired for the Medium Deep Survey (MDS) and the Groth/Westphal Sur…
Quantitative Morphology of Moderate Redshift Galaxies : How Many Peculiars are There ?
A. Naim, K. U. Ratnatunga, R. E. Griffiths
The advent of the Hubble Space Telescope (HST) has provided images of galaxies at moderate and high redshifts and changed the scope of galaxy morphologies considerably. It is evide…
Compact Nuclei in Moderately Redshifted Galaxies
Vicki L. Sarajedini, Richard F. Green, Richard E. Griffiths +1
The Hubble Space Telescope WFPC2 is being used to obtain high-resolution images in the V and I bands for several thousand distant galaxies as part of the Medium Deep Survey (MDS).…
WFPC2 Observations of the Cooling Flow Elliptical in Abell 1795
Jason Pinkney, Jon Holtzman, Chris Garasi +3
We present WFPC2 images of the core of the cooling flow cD galaxy in Abell 1795. An irregular, asymmetric dust lane extends 7 \h75 kpc in projection to the north-northwest. The dus…
A deep ROSAT Survey - XII. The X-ray spectra of faint ROSAT sources
Omar Almaini, Tom Shanks, Brian J. Boyle +4
Optical spectroscopy has enabled us to identify the optical counterparts to over 200 faint X-ray sources to a flux limit of S_(0.5-2keV)=4x10^-15 erg s^-1 cm^-2 on 5 deep ROSAT fie…
A deep ROSAT Survey X: X-ray Luminous Narrow Emission Line Galaxies
Richard E. Griffiths, Roberto Della Ceca, Ioannis Georgantopoulos +4
X-ray luminous narrow emision-line galaxies (NELG) have been previously identified and proposed as an important class of extragalactic X-ray sources, with a potentially significant…
Using Oblique Decision Trees for the Morphological Classification of Galaxies
E. Owens, R. E. Griffiths, K. U. Ratnatunga
We discuss the application of a class of machine learning algorithms known as decision trees to the process of galactic classification. In particular, we explore the application of…
Luminosity Functions of Elliptical Galaxies at z < 1.2
Myungshin Im, Richard E. Griffiths, Kavan U. Ratnatunga +1
The luminosity functions of E/S0 galaxies are constructed in 3 different redshift bins (0.2 < z < 0.55, 0.55 < z < 0.8, 0.8 < z < 1.2), using the data from the Hubble Space Telesco…