arXiv subjects
Publications and source records attributed to O. Gerhard.
We briefly describe the properties of the confirmed spectroscopic sample of intracluster planetary nebulae recently discovered in the Virgo cluster. We find 23 bonafide intracluster planetary nebulae and 8 high redshift (z ~ 3.1) Lyalpha emitters identified by their broad asymmetric emission line.
We present a study of the kinematics of the outer regions of the early-type galaxy NGC 1316, based on radial velocity measurements of 43 planetary nebulae as well as deep integrated-light absorption line spectra. The smoothed velocity field of NGC 1316 indicates fast rotation at a distance of 16 kpc, possibly associated with an elongated feature orthogonal to the inner dust lanes. The mean square stellar velocity is approximately independent of radius, and the estimated total mass of the system is 2.6 x 10^11 M_sun within a radius of 16 kpc, implying an integrated mass-to-light ratio of M/L_B = 8.
We examine the left-right asymmetry in the cleaned COBE/DIRBE near-infrared data of the inner Galaxy and show (i) that the Galactic bar is probably not seen very nearly end-on, and (ii) that even if it is, it is not highly elongated. The assumption of constant mass-to-light ratio is used to derive simulated terminal-velocity plots for the ISM from our model luminosity distributions. By comparing these plots with observed terminal velocities we determine the mass-to-light ratio of the near-IR bulge and disk. Assuming that all this mass contributes to gravitational microlensing we compute optical depths $τ$ for microlensing in Galactic-centre fields. For three models with bar major axis between $10°-25°$ from the Sun-Galactic Center line, the resulting optical depths in Baade's window lie in the range $0.83\times10^{-6} \lta τ\lta 0.89\times10^{-6}$ for main-sequence stars and $1.2\times10^{-6} \lta τ\lta 1.3\times10^{-6}$ for red-clump giants. We discuss a number of uncertainties including possible variations of the near-infrared mass-to-light ratio. We conclude that, although the values predicted from analyzing the COBE and gas velocity data are inconsistent at the $2-2.5σ$ level with recent observational determinations of $τ$, we believe they should be taken seriously.