We conducted a panoramic spectroscopic campaign with MOSCA at the Calar Alto observatory. We acquired spectra of more than 500 objects. Approximately 150 of these spectra were of galaxies that are members of six different clusters, which differ in intrinsic X-ray luminosity. The wavelength range allows us to quantify the star formation activity by using the OII and the Halpha lines. This activity is examined in terms of the large-scale environment expressed by the clustercentric distance of the galaxies as well as on local scales given by the spatial galaxy densities. A global suppression of star-formation is detected in the outskirts of clusters, at about 3Rvir. Galaxies with ongoing star-formation have similar activity, regardless of the environment. Therefore, the decline of the star-formation activity inside the investigated clusters is driven mainly by the significant change in the fraction of active versus passive populations. This suggests that the suppression of the star-formation activity occurs on short timescales. We detect a significant population of red star-forming galaxies whose colors are consistent with the red-sequence of passive galaxies. They appear to be in an intermediate evolutionary stage between active and passive types. Since a suppression of star-formation activity is measured at large clustercentric distances and low projected densities, purely cluster-specific phenomena cannot fully explain the observed trends. Therefore, as suggested by other studies, group preprocessing may play an important role in transforming galaxies before they enter into the cluster environment. Since models predict that a significant fraction of galaxies observed in the outskirts may have already transversed through the cluster center, the effects of ram-pressure stripping cannot be neglected. (ABRIDGED)
We perform statistical analyses to study the infall of galaxies onto groups and clusters in the nearby Universe. The study is based on the UZC and SSRS2 group catalogs and peculiar velocity samples. We find a clear signature of infall of galaxies onto groups over a wide range of scales 5 h^{-1} Mpc<r<30 h^{-1} Mpc, with an infall amplitude on the order of a few hundred kilometers per second. We obtain a significant increase in the infall amplitude with group virial mass ( M_{V} ) and luminosity of group member galaxies ( L_{g} ). Groups with M_{V} <10^{13} M_{\odot} show infall velocities V_{i…
为银河系中心区域制作了氨排放的VLA图。NH_3（1，1）和NH_3（2，2）跃迁分别出现在3个2'× 2'视场中，它们覆盖了Sgr A ~* 及其以南3'区域，在围绕Sgr A ~* 的中央3秒差距区域，我们发现了与环核盘（CND）有关的发射，无论是从形态学上还是从运动学上都是如此。这个中心发射连接到一个长的，狭窄的2 pc x 10 pc的cluerous分子气体流光位于南部，这似乎是携带气体从附近的20公里/秒的巨大分子云（GMC）的环核区域。我们发现沿流光的速度梯度，随着气体接近Sgr A*，速度逐渐变高。流光在CND的位置处停止，其中NH3发射的线宽急剧增加。这可能是吸积到CND上的运动学特征。NH3（2，2）/NH3（1，1）发射的比率表明气体在位于CND东部边缘内的流光的北端被加热。气体的形态学、运动学和温度梯度都表明南部流光位于银河系中心，并与环核区域相互作用。
Infall of the Elliptical Galaxy NGC 1404 into the Fornax Cluster
We use three Chandra observations, totalling 134.3 ks, to constrain the dynamical motion of NGC1404 falling towards the dominant elliptical NGC1399 through the Fornax ICM. NGC1404's surface brightness profile shows a sharp edge \~8 kpc from its center in the direction of NGC 1399, characteristic of jump-like temperature and density discontinuities from ram-pressure stripping of the galaxy gas. We find the temperature of the galaxy gas inside the edge is \~2.8 times cooler (kT=0.55^{+0.01}_{-0.02} keV; abundance A = 0.73^{+0.65}_{-0.16} solar) than the cluster gas (kT,A = 1.53^{+0.10}_{-0.13} k…
The Distribution of Mass and Light in Cluster Infall Regions
CAIRNS（Cluster And Infall Region Nearby Survey）是一个大型的光谱调查项目，对9个邻近的富星系团周围的坠落区域进行调查。我描述的调查和使用的星系在下落区的运动学来估计集群的质量配置文件。在小半径，这些质量分布是一致的独立质量估计从X射线观测和牛仔裤分析。我证明了依赖于环境的质光比结合这些质量配置文件与两微米全天巡天（2 MASS）测光。在这些星系团中，近红外线比质量更长，这表明密集的星系团核心在形成星系方面效率较低，并且/或者在破坏星系方面效率更高。在大的半径上，星系团落区中的星系群与场中的星系群非常相似。因此，在这些半径处的质光比应该是一个很好的探测全局质光比的方法。下落区的质光比产生了令人惊讶的低估计值$Ω_m \sim 0.1$。
Evolutionary Synthesis Models for Galaxy Transformation in Clusters
在丰富的本地星系团的星系人口的比例显示四分之一的椭圆星系，四分之二的S0星系，和四分之一的旋涡星系。对红移为0.5的星系团的观测显示出明显不同的比例，主要的星系类型是螺旋星系，只有四分之二，而S0星系的数量减少到四分之一（Dressler et al.1997）。这显示了自红移0.5以来星系群中星系数量的演变，人们怀疑星系在进入星系团期间的转变过程是造成这种变化的原因。这些可能是合并，星爆或冲压压力剥离。我们使用我们的进化合成模型来描述各种可能的影响，这些相互作用对恒星形成的螺旋星系落入集群。我们研究了不同强度的恒星爆发以及不同时期恒星形成的截断对不同光谱类型的模型星系的颜色和光度演化的影响。作为第一个应用程序，我们提出了我们的模型与观察到的本地S0星系人口的性质，以限制可能的S0形成机制的集群的比较。计划将来将其应用于其他类型的星系。
