M51的观测研究进展

Observational and Research Progress of the M51 Galaxy

M51系统包含巨旋涡星系M51和相对较大且较近的伴星系NGC 5195。M51离银河系较近,由尘埃消光带来的观测不确定性也就不十分显著,从而可以得到较详细的星系结构。自M51被发现至今,从射电波段到X射线波段都已获得了丰富的观测资料。主要介绍了M51的多波段观测成果和数值模拟研究,并概述了对其伴星系NGC 5195的观测。

The M51 system consists of a grand-design spiral galaxy and a relatively large close companion, NGC 5195. Because M51 is nearby and nearly face-on to us, its structure can be observed in great detail and with a minimum of obscuration from dust. As a result, this galaxy has been thoroughly observed at wavelengths from radio to X-ray. Due to the rich archive of observational data, its structure, dynamical process, star formation mechanism and some other important properties have been analyzed by many authors. In the center of M51, there is a Seyfert 2 or LINER type AGN which radius is 100 pc. The mass within 70 pc in the center is （4-7） × 10^6M⊙, this indicates there may be a black hole there. The disk of M51 can be divided into two parts, the inner disk arounding the nucleus cuts off at 1350 pc, from this radius to 10kpc is the outer disk. In contrast, the companion, NGC 5195 is small and faint, and heavy dust from the arm of M51 in the foreground obscures its optical radiation. M51 has many interesting properties different from other normal spiral galaxies, such as the wide open spiral arm, the long HI tidal tail and the huge distorted gas ring around the outer disk, these may be related to the interaction effects. Actually, the dynamical modeling history of M51 is long, in the early stage of astronomical numerical simulation, Toomre and Toomre have given a simple simulation of M51 to study its tidal effect. In 1990, the discovery of M51^1s long HI tidal tail made the astrophysicist shift the preferred collision time of M51 and NGC 5195 to somewhat later times in order to give the tail more time to develop. More recently, Salo and Laurikainen suggested that a multiplepassage model might be more appropriate for the system, such a scenario appears to do a better job of explaining NGC 5194＇s HI velocity field, but the predicted structure of the HI tidal tail is more complex than its observation. In this paper, we review literature of multi-wavelength observations and recent research results of M51, discuss the improvements and drawbacks of its simulation results and also summarize the available observations of NGC 5195.