We present a deep broadband optical imaging study of a complete sample of luminous elliptical galaxies (M_B<-20) at distances 15 Mpc - 50 Mpc, selected from the Tully catalog of nearby galaxies. The images are flat to ~0.35% across the 20' field and reach a V band depth of 27.7 mag arcsec^-2. We derive an objective tidal interaction parameter for all galaxies and find that 73% of them show tidal disturbance signatures in their stellar bodies. This is the first time that such an analysis is done on a statistically complete sample and it confirms that tidal features in ellipticals are common even in the local Universe. From the dynamical time of the sample galaxies at the innermost radius where tidal features are detected we estimate the mass assembly rate of nearby ellipticals to be dM/M 0.2 per Gyr with large uncertainty. We explore the relation between gravitational interaction signatures and the galaxy environment and find that galaxies in clusters are less disturbed than group and field galaxies. We also study how these interactions affect the broadband colors of ellipticals and find a moderate correlation, suggesting that the mergers are not accompanied by significant star-formation. Lastly, we find no correlation between AGN activity, as measured by 6cm radio emission, and large scale tidal distortions. This implies that gravitational interactions are not the only, and perhaps not the most important, trigger of nuclear activity. In summary, we find that elliptical galaxies in groups and low density environments continue to grow at the present day through mostly "dry" mergers involving little star formation.
When galaxies align: intrinsic alignments of the progenitors of elliptical galaxies in the Horizon-AGN simulation
今天的椭圆星系似乎与宇宙的大尺度结构成一直线，但它们何时获得这种排列仍然是一个悬而未决的问题。目前的观测数据不足以提供约束的时间演化的内在的路线，因此现有的模型范围从假设星系获得一些原始的排列在形成，建议他们立即作出反应的潮汐相互作用的大尺度结构。利用宇宙学流体动力学模拟Horizon-AGN，我们测量了星系长轴与潮汐场本征矢量之间的相对排列随红移的变化。我们专注于约束的大质量$z=0$椭圆星系，在低红移的主要弱透镜污染物的主要祖先的排列的时间演化。我们表明，这个人口，在$z=0$有一个恒星质量以上$10^{10.4}$ M $_\odot$，过渡到没有对齐的潮汐场在$z=3$，一个显着的对齐由$z=1$。从$z=0.5$开始，它们以近似恒定的水平保持其对齐，直到$z=0$。我们发现了一个质量依赖性的椭圆祖细胞的对齐信号，即椭圆，是质量较低的今天（$10^{10.4}<M/{\rm M}_\odot<10^{10.7}$）不成为对齐，直到后来的红移（$z<2$），相比更大的同行。我们还提出了一个扩展的研究祖先的路线在参数空间的恒星质量和星系动力学，形状定义和潮汐场平滑的影响。
Project Dinos II: Redshift evolution of dark and luminous matter density profiles in strong-lensing elliptical galaxies across 0.1 < z < 0.9
University of California, Los Angeles（加州大学洛杉矶分校）；Kavli Institute for Cosmological Physics, University of Chicago（芝加哥大学卡弗里宇宙物理研究所）；Department of Astronomy and Astrophysics, University of Chicago（芝加哥大学天文与天体物理系）；Shanghai Jiao Tong University（上海交通大学）；Stony Brook University（石溪大学）；University of Oxford（牛津大学）；Institute of Cosmology and Gravitation, University of Portsmouth（朴茨茅斯大学宇宙学与引力研究所）；Department of Physics, University of Chicago（芝加哥大学物理系）
