潮汐扰动矮星系的蜕变
The Metamorphosis of Tidally Stirred Dwarf Galaxies
摘要：
本文采用高分辨率N-Body/SPH方法模拟了在银河系大质量暗物质晕中沿束缚轨道运动的旋转支撑矮不规则星系，结果表明，矮星系模型的盘面密度和暗物质晕的质量和大小与冷暗物质宇宙演化的预测一致。我们发现，银河系的强潮汐场决定了严重的质量损失，在他们的晕和磁盘，并诱导酒吧和弯曲的不稳定性，将低表面亮度的矮星（LSB）到矮椭球（dSphs）和高表面亮度的矮星（HSB）到矮椭圆（dEs）在不到10 Gyr。最后的残留物的中心速度分散的范围是8-30公里/秒，其最终的$v/σ$下降到值$< 0.5$，以及匹配的运动学的早期型矮星。这种转变需要矮星系的轨道时间是$\simlt 3-4$ Gyr，这意味着它的晕圈与星系形成的分级模型所预测的一样大，而且延伸得很广，从而解释了银河系中最远的dSPh卫星狮子座I和狮子座II的起源。只有中心暗物质密度与天龙座和小熊座一样高的矮星才能在银河系附近存活10 Gyr：这在分层模型中自然实现，其中致密天体由于其早期形成时代而应该具有较小的轨道时间。部分气体被剥离，部分由于棒而被漏斗状地输送到中心，在HSB中产生一个强烈的恒星形成爆发，在LSB中产生较小的多个爆发。扩展的低表面亮度恒星流和气体流源自LSB，当沿着视线投射时，可能导致高估束缚残余物的质光比$\simlt 2$，
英文摘要：
We present results from high-resolution N-Body/SPH simulations of rotationally supported dwarf irregular galaxies moving on bound orbits in the massive dark matter halo of the Milky Way.The dwarf models span a range in disk surface density and the masses and sizes of their dark halos are consistent with the predictions of cold dark matter cosmogonies. We show that the strong tidal field of the Milky Way determines severe mass loss in their halos and disks and induces bar and bending instabilities that transform low surface brightness dwarfs (LSBs) into dwarf spheroidals (dSphs) and high surface brightness dwarfs (HSBs) into dwarf ellipticals (dEs) in less than 10 Gyr. The final central velocity dispersions of the remnants are in the range 8-30 km/s and their final $v/σ$ falls to values $< 0.5$, matching well the kinematics of early-type dwarfs. The transformation requires the orbital time of the dwarf to be $\simlt 3-4$ Gyr, which implies a halo as massive and extended as predicted by hierarchical models of galaxy formation to explain the origin of even the farthest dSph satellites of the Milky Way, Leo I and Leo II. Only dwarfs with central dark matter densities as high as those of Draco and Ursa Minor can survive for 10 Gyr in the proximity of the Milky Way: this is naturally achieved within hierarchical models, where the densest objects should have small orbital times due to their early formation epochs. Part of the gas is stripped and part is funneled to the center due to the bar, generating one strong burst of star formation in HSBs and smaller, multiple bursts in LSBs. Extended low-surface brightness stellar and gaseous streams originate from LSBs and, when projected along the line of sight, can lead to overestimate the mass-to-light ratio of the bound remnant by a factor $\simlt 2$,
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