When a satellite galaxy falls into a massive dark matter halo, it suffers from the dynamical friction force which drags it into the halo＇s center, where it finally merges with the central galaxy. The time interval between entry and merger is called the dynamical friction timescale （Tdf）. Many studies have been dedicated to deriving Tdf using analytical models or N-body simulations. These studies have obtained qualitative agreements on how Zdf depends on the orbital parameters, and the mass ratio between the satellite and the host＇s halo. However, there are still disagreements on deriving an accurate form for Tdf. We present a semi-analytical model to predict Tdf and we focus on interpreting the discrepancies among different studies. We find that the treatment of mass loss from the satellite by tidal stripping dominates the behavior of Tdf. We also identify other model parameters which affect the predicted Tdf.
We analyze the optical spectra of Fairall 9,a luminous Seyfert 1 galaxy.They are obtained from the AGN Watch program that has monitored this object for 9 months.The flux and variation of the optical FeII complex is measured using multi-component profile modeling with FeⅡ templates.A convincing intrinsic Baldwin Effect(BEff) of optical FeⅡ emission blends in Fairall 9 is discovered for the first time.The variation of FeⅡ/Hβ(RFe) in Fairall 9 is obtained.We also detect a marginal anti-correla tion between RFe and the continuum flux in its spectra.This anti-correlation and the relatively broad profile of Hβ in this galaxy support the dichotomy reported by Wang et al.(2005).
HAN XuHuiWANG JingWEI JianYanYANG DaWeiHOU JinLiang
A computational code is developed to help identify metal absorption lines in high resolution QSO spectra, especially in the Lyα forest. The input to the code includes a list of line central wavelengths, column densities and Doppler widths. The code then searches for candidate metal absorption systems and assesses the probability that each system could be real. The framework of the strategy we employ is described in detail and we discuss how to estimate the errors in line profile fitting that are essential to identification. A series of artificial spectra is constructed to calibrate the performance of the code. Due to the effects of blending and noise on Voigt profile fitting, the completeness of the identification depends on the column density of absorbers. For intermediate and strong artificial metal absorbers, more than 90% could be confirmed by the code. The results of applying the code to the real spectra of QSOs HS0757＋5218 and Q0100＋1300 are also presented.
Xi-Heng ShiDavid TytlerJin-Liang HouDavid KirkmantJeffery LeeBenjamin Ou
