One of the key predictions of the merger hypothesis for the origin of early-type (elliptical and lenticular) galaxies is that tidally-induced asymmetric structure should correlate with signatures of a relatively young stellar population. Such a signature was found by Schweizer and Seitzer (1992; AJ, 104, 1039) at roughly 4sigma confidence. In this paper, we revisit this issue with a nearly ten-fold larger sample of 0.01<z<0.03 galaxies selected from the Two Micron All-Sky Survey and the Sloan Digital Sky Survey. We parameterize tidal structure using a repeatable algorithmic measure of asymmetry, and correlate this with color offset from the early-type galaxy color-magnitude relation. We recover the color offset-asymmetry correlation; furthermore, we demonstrate observationally for the first time that this effect is driven by a highly-significant trend towards younger ages at higher asymmetry values. We present a simple model for the evolution of early-type galaxies through gas-rich major and minor mergers that reproduces their observed build-up from z=1 to the present day and the distribution of present-day colors and ages. We show using this model that if both stellar populations and asymmetry were ideal `clocks' measuring the time since last major or minor gas-rich interaction, then we would expect a rather tight correlation between age and asymmetry. We suggest that the source of extra scatter is natural diversity in progenitor star formation history, gas content, and merger mass ratio, but quantitative confirmation of this conjecture will require sophisticated modeling. We conclude that the asymmetry-age correlation is in basic accord with the merger hypothesis, and indicates that an important fraction of the early-type galaxy population is affected by major or minor mergers at cosmologically-recent times.
Intrinsic handedness in O1-O4a black-hole mergers: probing orbital precession, remnant retention in dense environments and cosmological mirror asymmetry
Instituto Galego de Física de Altas Enerxías, Universidade de Santiago de Compostela（加利西亚高等物理研究所，圣地亚哥-德孔波斯特拉大学）；The Chinese University of Hong Kong（香港中文大学）；Universidad Carlos III de Madrid（马德里卡洛斯三世大学）；Universitat de València（瓦伦西亚大学）；Max Planck Institute for Gravitational Physics (Albert Einstein Institute)（马克斯·普朗克引力物理研究所（爱因斯坦研究所））
Testing the key role of the stellar mass-halo mass relation in galaxy merger rates and morphologies via DECODE, a novel Discrete statistical sEmi-empiriCal mODEl
The Complex Structure of the Multi-Phase Galactic Wind in a Starburst Merger
通过Na I D $λλ5890, 5896$吸收线偶线，在许多超亮红外星系（ULIRGs）中观测到了中性外流。首次利用Gemini North上的积分场单元（IFU）对ULIRG（F10565+2448）中的冷中性外流进行了二维运动学分析，并观测了Na I D特征。同时，我们用[NII]和H $α$的发射线绘制了电离流出图。我们发现一个系统的旋转曲线，这是一致的分子盘从以前的CO观测确定的旋转。吸收线显示出核流出的证据，径向范围至少为3千秒差距，与以前的观测结果一致。Na I D线的强度有很强的，空间分辨的相关性与变红，这表明尘埃是存在于流出。令人惊讶的是，中性气体的流出速度显示出强烈的不对称性，其形式为与盘旋转符号相反的主轴梯度。这与随星系旋转的夹带物质或倾斜的短轴流出不一致。我们假设这种不寻常的行为是由于周围气体分布的不对称性。我们还看到不对称的电离流出的证据，在发射线速度图，这似乎是从中性流出解耦。我们的研究结果加强了这样一个假设，即ULIRG外流在形态上不同于那些在更安静的盘星系。
Quantified HI Morphology IV: The Merger Fraction and Rate in WHISP
螺旋星系氢原子盘的形态是受到引力相互作用（如星系合并）扰动的第一个组成部分。我们使用一个简单的参数化的形态Westerbork HI螺旋项目（WHISP）的HI柱密度图，以选择那些可能正在经历一个显着的相互作用的星系。合并星系占据了由不对称性（A）、20%最亮像素对列密度图二阶矩的相对贡献（M20）和所有像素上二阶矩的分布（GM）定义的参数空间的特定部分。基于它们的HI形态，我们发现13%的WHISP星系处于相互作用（浓度-M20）中，只有7%的星系基于数据立方体中的密切同伴。这种明显的差异可以归因于可见度时间尺度的差异：合并在0.5 Gyr时可以被识别为近对，但在~1 Gyr时可以通过它们被干扰的HI形态来识别。用体积合并率表示，两个估计值非常吻合：配对和形态扰动的HI盘分别为7 x 10^-3和6.8 x 10^-3合并Gyr^-1 Mpc^-3。我们的合并分数的一致性，如斯隆数字巡天更大的调查公布，表明HI形态可以是一个非常可行的方式来确定合并在一个大型HI调查。卷合并率的相对高的值可能是选择或WHISP卷的偏差。计划中的MeerKAT、ASKAP和WSRT/APERTIF射电天文台提供的高分辨率HI数据的预期收益将揭示合并在局部宇宙中的重要性，并随着SKA的出现，揭示整个宇宙时代的重要性。
