M33星系的分裂从其扩展的气体结构中可以明显看出。我们提出了来自银河阿雷西博L波段馈源阵列HI（GALFA-HI）调查的新数据，显示了M33中性氢的完整范围和详细的空间和运动学结构。在远紫外线（FUV）的追踪下，发现M33的HI质量（M_HI（tot）=1.4 x 10^9 Msun）超过18%都在恒星形成盘之外。最明显的特征是延伸的弯曲，从北部弯曲到盘的弧形，弥漫的气体包围着星系，以及南部的云带着一条回到星系的细丝。这些特征从星系中心延伸到22 kpc（从FUV盘边缘延伸到18 kpc），气体直接连接到M33的盘。只有五个离散云（即，在位置-速度空间中与M33没有直接联系的气体）在M33附近被编目，这些云显示出与银河系和M31晕云相似的性质。M33的气体特征很可能是由M31在1-3 Gyr前对M33的潮汐破坏造成的，轨道分析表明，在M33的大部分可能轨道中，潮汐半径< 15 kpc。M33现在已经超出了M31的破坏性引力影响，气体似乎正在返回M33的圆盘并重新分配其恒星形成燃料。M33的高平均速度色散（~18.5 km/s）也可能与之前的相互作用和高恒星形成率相一致。M33要么在接下来的几个Gyrs内耗尽其恒星形成燃料，要么最终成为M31的恒星形成燃料。后者代表了一个巨大的气态卫星被螺旋星系吸积，类似于麦哲伦云与银河系的关系。
英文摘要：
The disruption of the M33 galaxy is evident from its extended gaseous structure. We present new data from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) Survey that show the full extent and detailed spatial and kinematic structure of M33's neutral hydrogen. Over 18% of the HI mass of M33 (M_HI(tot) =1.4 x 10^9 Msun) is found beyond the star forming disk as traced in the far-ultraviolet (FUV). The most distinct features are extended warps, an arc from the northern warp to the disk, diffuse gas surrounding the galaxy, and a southern cloud with a filament back to the galaxy. The features extend out to 22 kpc from the galaxy center (18 kpc from the edge of the FUV disk) and the gas is directly connected to M33's disk. Only five discrete clouds (i.e., gas not directly connected to M33 in position-velocity space) are catalogued in the vicinity of M33, and these clouds show similar properties to Galactic and M31 halo clouds. M33's gaseous features most likely originate from the tidal disruption of M33 by M31 1-3 Gyr ago as shown from an orbit analysis which results in a tidal radius < 15 kpc in the majority of M33's possible orbits. M33 is now beyond the disruptive gravitational influence of M31 and the gas appears to be returning to M33's disk and redistributing its star formation fuel. M33's high mean velocity dispersion in the disk (~18.5 km/s) may also be consistent with the previous interaction and high rate of star formation. M33 will either exhaust its star formation fuel in the next few Gyrs or eventually become star formation fuel for M31. The latter represents the accretion of a large gaseous satellite by a spiral galaxy, similar to the Magellanic Clouds' relationship to the Galaxy.
The Minor-Merger Driven Nuclear Activity in Seyfert Galaxies: A Step toward the Simple Unified Formation Mechanism of Active Galactic Nuclei in the Local Universe
Nuclear Bar, Star Formation and Gas Fueling in the Active Galaxy NGC 4303
哈勃空间望远镜（HST）WFPC 2和NICMOS图像的组合被用来研究附近的活动星系NGC 4303的中央300 pc内的气体/尘埃和恒星结构。NICMOS H波段（F160 W）图像显示了一个明亮的核心和一个直径为250 pc的核细长棒状结构。棒的中心是明亮的核心，它的主轴是在proyection方向沿着最近检测到的核气体旋转盘的自旋轴（Colina & Arribas 1999）。V-H（F606 W-F160 W）图像揭示了复杂的气体/尘埃分布，具有半径约225秒差距的双臂螺旋结构。西南臂由年轻的恒星形成结追踪，而东北臂则由尘埃带的存在探测到。这些螺旋不具有光滑的结构，而是由较小的絮状螺旋或絮状结构制成。恒星形成节点的星等和颜色是典型的年轻恒星星团，质量为0.5到1 x $10^5 M_{solar}, and ages of 5 to 25 million years. The overall structure of the nuclear spirals as well as the size, number and masses of the star-forming knots are explained in the context of a massive gaseous nuclear disk subject to self-gravitational in…
