Using the spectroscopic New York University Value-Added Galaxy Catalogue and the photometric photo-z catalogues of the Sloan Digital Sky Survey Data Release 7, we have explored the satellite distribution around ~1000 massive (M_star > 2x10^11 M_sun) visually classified elliptical galaxies down to a satellite mass ratio of 1:400 (i.e. 5x10^8 < M_sat < 2x10^11 M_sun). Our host galaxies were selected to be representative of a mass complete sample. The satellites of these galaxies were searched within a projected radial distance of 100 kpc to their hosts. We have found that only 20-23 per cent of the massive ellipticals have at least a satellite down to a mass ratio 1:10. This number increases to 45-52 per cent if we explore satellites down to 1:100 and is $>$60-70 per cent if we go further down to 1:400. The average projected radial distance of the satellites to their hosts is ~59 kpc (which can be decreased at least down to 50 kpc if we account for incompleteness effects). The number of satellites per galaxy host only increases very mildly at decreasing the satellite mass. The fraction of mass which is contained in the satellites down to a mass ratio of 1:400 is 8 per cent of the total mass contained by the hosts. Satellites with a mass ratio from 1:2 to 1:5 (with ~28 per cent of the total mass of the satellites) are the main contributor to the total satellite mass. If the satellites eventually infall into the host galaxies, the merger channel will be largely dominated by satellites with a mass ratio down to 1:10 (as these objects have 68 per cent of the total mass in satellites).
Reionization of the Milky Way, M31, and their satellites I: reionization history and star formation
对银河系（MW）、M31及其附近的本星系群（LG）的观测可以提供有关再电离源的线索。我们提出了一套辐射转移模拟的基础上提供的约束本地UniversE模拟（CLUES）项目，旨在重建本地宇宙，包括一个现实的MW-M31对和附近的室女座的初始条件。我们的盒子大小（91兆秒差距）是足够大的，以纳入电离光子的LG的相关来源。我们采用了一系列的源模型，模仿辐射反馈之间的暗物质晕$10^{8}-10^{9}$ M $_{\odot}$的潜在影响。虽然LG主要是以由内而外的方式再电离，但其电离的最后40%显示出一些外部影响。对于LG卫星，我们没有发现证据表明它们的再电离红移与卫星的现今质量或与中央星系的距离有关。我们发现，不到20%的MW和M31卫星在全球再电离结束之前经历了任何恒星形成。这些卫星中大约有5%可以归类为化石，这意味着大多数恒星形成都发生在这些早期。更大质量的卫星在全球再电离结束之前有更多的累积恒星形成，但分散是显着的，特别是在低质量端。现今的质量和与中央星系的距离对于卫星星系中是否存在古老的恒星星族是很难预测的。
The luminosity function of diverse satellite galaxy systems
麦克马斯特无偏星系巡天（MUGS）的高分辨率SPH星系被用来检查16个模型宿主星系的卫星系统。每个星系都有不同的质量，角动量和合并历史，产生了丰富的卫星光度函数。通过对遥远卫星系统的新观测，我们可以将这些光度函数与本星系群以外的卫星系统进行比较。我们发现，我们的模拟的光度函数比较好的观测时，光度函数根据主机质量缩放。我们使用最近发现的矮卫星和遥远卫星系统中的宿主质量之间的关系（Trentham & Tully 2009）来规范化银河系的理论完整光度函数（Koposov et al. 2008）。卫星的光度函数表示为宿主质量的函数，由dN/dM_V= 3.5 x M_host^（0.91）x 10^（0.1 x M_V-10.2）给出，其中宿主质量以M_sun为单位。宿主星系的质量可以用来预测矮卫星星系的数量，甚至当分别考虑螺旋星系和椭圆星系时，这种关系也成立。
A new population of recently quenched elliptical galaxies in the SDSS
We use the Sloan Digital Sky Survey to investigate the properties of massive elliptical galaxies in the local Universe (z \leq 0.08) that have unusually blue optical colors. Through careful inspection, we distinguish elliptical from non-elliptical morphologies among a large sample of similarly blue galaxies with high central light concentrations (c_r \geq 2.6). These blue ellipticals comprise 3.7 per cent of all c_r \geq 2.6 galaxies with stellar masses between 10^10 and 10^11 h^{-2} { \rm M}_{ \sun }. Using published fiber spectra diagnostics, we identify a unique subset of 172 non-star-formi…
The evolution of the scatter of the cosmic average color-magnitude relation: Demonstrating consistency with the ongoing formation of elliptical galaxies
