Quantitative analysis of galaxy-galaxy lensing

Gravitational light deflection due to mass along the line-of-sight will distort the images of background sources. This effect has been used successfully to investigate the mass distribution of galaxy clusters. Although an individual galaxy is not massive enough to cause a detectable lensing distortion in the background population, this effect can be measured statistically for a population of galaxies, and a first detection was reported recently by Brainerd, Blandford and Smail (BBS). In this paper we explore a quantitative and efficient method to constrain the halo properties of distant galaxy populations through galaxy-galaxy lensing and show that the mean masses and sizes of halos can be estimated accurately, without excessive data requirements. Specifically, we propose a maximum-likelihood analysis which takes full account of the actual image ellipticities, positions and apparent magnitudes. We apply it to simulated observations, using the same model for the lensing galaxy population as in BBS, where the galaxy halos are described by isothermal spheres with velocity dispersion #sigma#, truncated at a radius s. Both parameters are assumed to scale with the luminosity of the galaxy. The best fitting values, #sigma#* and s*, corresponding to an L*-galaxy, are then determined with the maximum-likelihood analysis28 refs.Available from TIB Hannover: RR 4697(928) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Pressure supported ionized gas in SO galaxies

Rotation curves and velocity dispersion profiles are presented for both the stellar and gaseous components of a sample of S0 galaxies. In all galaxies the central velocity dispersion of the ionized gas exceeds 150 km s"-"1. In some galaxies the gas dispersion remains as high as the stellar one over an extended radial range, showing that random motions are crucial for the dynamical support of the gas. Such a pressure support may explain why the observed gas rotation curves in galaxy bulges often fall short of the circular velocity predicted from the stellar kinematic models. It is suggested that, in addition to the acquisition of external material, some of the observed gas in S0 galaxies may have been shed from bulge stars. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman