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Paper: Mergers of Galaxies and Orientation of Giant Elliptical Galaxies
Volume: 408, The Starburst−AGN Connection
Page: 328
Authors: Jing, Y.P.; Jiang, C.Y.; Okunmura, T.; Faltenbacher, A.; Li, C.; Lin, W.P.
Abstract: In this talk, we present our recent study of galaxy mergers in a high-resolution cosmological hydro/N-body simulation with star formation, and compare the measured merger timescales with theoretical predictions based on the Chandrasekhar formula. In contrast to Navarro et al., our numerical results indicate, that the commonly used equation for the merger timescale given by Lacey and Cole, systematically underestimates the merger timescales for minor mergers and overestimates those for major mergers. This behavior is partly explained by the poor performance of their expression for the Coulomb logarithm, ln(mpri/msat). The two alternative forms ln(1 + mpri/msat) and 1/2 ln[1 + (mpri/msat)2] for the Coulomb logarithm can account for the mass dependence of merger timescale successfully, but both of them underestimate the merger time scale by a factor 2. Since ln(1+mpri/msat) represents the mass dependence slightly better we adopt this expression for the Coulomb logarithm. Furthermore, we find that the dependence of the merger timescale on the circularity parameter . is much weaker than the widely adopted power-law ε0.78, whereas 0.94 ∗ ε0.60 + 0.60 provides a good match to the data. Based on these findings, we present an accurate and convenient fitting formula for the merger timescale of galaxies in cold dark matter models. Elliptical galaxies, which are usually expected to be the remnants of the galaxy mergers, are examined with the SDSS luminous red galaxies about their orientation with respect to their host halos. Using the ellipticity-ellipticity correlation function and the gravitational shear . intrinsic ellipticity (GI) correlation function, we have accurately determined the distribution of the orientation angle which will have interesting implications for future studies of galaxy mergers and for weak lensing studies.
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