We present simulations of dry-merger encounters between pairs of elliptical galaxies with dark matter halos. The aim of these simulations is to study the intergalactic stellar populations produced in both parabolic and hyperbolic encounters. We model progenitor galaxies with total-to-luminous mass ratios M_T/M_L 3 and 11. The initial mass of the colliding galaxies are chosen so that M_1/M_2 and 10. The model galaxies are populated by particles representing stars, as in Stanghellini et al. (2006), and dark matter. Merger remnants resulting from these encounters display a population of unbounded particles, both dark and luminous. The number of particles becoming unbounded depends on orbital configuration, with hyperbolic encounters producing a larger luminous intracluster population than parabolic encounters. Furthermore, in simulations with identical orbital parameters, a lower M_T/M_L of the colliding galaxies produces a larger fraction of unbounded luminous particles. For each modeled collision, the fraction of unbounded to initial stellar mass is the same in all mass-bins considered, similarly to what we found previously by modeling encounters of galaxies without dark halos. The fraction of intergalactic to total luminosity resulting from our simulations is ~ 4% and ~ 6% for dark-to-bright mass rations of 10 and 2 respectively. These unbounded-to-total luminous fractions are down from 17 % that we had previously found in the case of no dark halos. Our results are in broad agreement with intergalactic light observed in groups of galaxies, while the results of our previous models without dark halos better encompass observed intracluster populations. We suggest a possible formation scenario of intergalactic stars.
最近的研究表明，遥远宇宙中的大质量星系是令人惊讶的紧凑，其典型尺寸比附近宇宙中同等质量的星系小三倍左右。有人认为，这些大质量星系通过一系列微小的合并，成长为类似于附近星系的系统。在这个模型中，星系的大小增长是一个固有的随机过程，并由此产生的大小光度关系预计有相当大的环境依赖的散射。为了测试小合并是否可以解释大质量星系的大小增长，我们使用一个新的大型数据库（Nair & Abraham 2010）仔细研究了附近椭圆星系的大小-光度关系的散射。我们证明，这种分散比以前假设的要小得多，甚至可能是如此之小，以挑战合并驱动的大规模椭圆形成的分层模型的可扩展性。
Formation of massive disk galaxies in the IllustrisTNG simulation
我们利用流体动力学模拟程序IllustrisTNG研究了大质量盘状星系的形成历史，以研究大质量盘状星系在宇宙时间中存活的原因。模拟中选取了83个星系，它们的M $_{*,z=0}$ $>8\times10^{10}$ M $_\odot$和运动学膨胀与总膨胀比小于$0.3$。我们发现，8.4%的这些巨大的盘星系有安静的合并历史，并保持磁盘形态，因为形成。54.2在历史上，100%的区域中，凸起成分显著增加，然后再次变为盘状，直到现在。其余37.3%的公司经历了重大的合并，但仍能保持不稳定。虽然合并，甚至主要合并并不总是把盘星系椭圆，我们研究合并的各种属性和合并残留物的形态之间的关系。我们发现一个强大的依赖主要合并轨道类型的残留形态。具体来说，主要合并与螺旋下降轨道大多导致磁盘占主导地位的残余物，和主要合并的正面星系星系碰撞大多形成椭圆星系。这种残余形态对轨道类型的依赖性比先前研究的对冷气体分数或合并系统的轨道构型的依赖性强得多。
Binary compact object coalescence rates: The role of elliptical galaxies
We estimate binary compact object merger detection rates for LIGO, including the binaries formed in ellipticals long ago. Specifically, we convolve hundreds of model realizations of elliptical- and spiral-galaxy population syntheses with a model for elliptical- and spiral-galaxy star formation history as a function of redshift. Our results favor local merger rate densities of 4 \times 10^{-3} {Mpc}^{-3}{Myr}^{-1} for binary black holes (BH), 3 \times 10^{-2} {Mpc}^{-3}{Myr}^{-1} for binary neutron stars (NS), and 10^{-2} {Mpc}^{-3}{Myr}^{-1} for BH-NS binaries. Mergers in elliptical galaxies a…
