We explore the galaxy-galaxy merger rate with the empirical model for galaxy formation, Emerge. On average, we find that between $2$ per cent and $20$ per cent of massive galaxies ($\log_{10}(m_{*}/M_{\odot}) \geq 10.3$) will experience a major merger per Gyr. Our model predicts galaxy merger rates that do not scale as a power-law with redshift when selected by descendant stellar mass, and exhibit a clear stellar mass and mass-ratio dependence. Specifically, major mergers are more frequent at high masses and at low redshift. We show mergers are significant for the stellar mass growth of galaxies $\log_{10}(m_{*}/M_{\odot}) \gtrsim 11.0$. For the most massive galaxies major mergers dominate the accreted mass fraction, contributing as much as $90$ per cent of the total accreted stellar mass. We reinforce that these phenomena are a direct result of the stellar-to-halo mass relation, which results in massive galaxies having a higher likelihood of experiencing major mergers than low mass galaxies. Our model produces a galaxy pair fraction consistent with recent observations, exhibiting a form best described by a power-law exponential function. Translating these pair fractions into merger rates results in an inaccurate prediction compared to the model intrinsic values when using published observation timescales. We find the pair fraction can be well mapped to the intrinsic merger rate by adopting an observation timescale that decreases linearly with redshift as $T_{\mathrm{obs}} = -0.36(1+z)+2.39$ [Gyr], assuming all observed pairs merge by $z=0$.
The concentration parameter is a key characteristic of a dark matter halo that conveniently connects the halo's present-day structure with its assembly history. Using 'Dark Sky', a suite of cosmological $N$-body simulations, we investigate how halo concentration evolves with time and emerges from the mass assembly history. We also explore the origin of the scatter in the relation between concentration and assembly history. We show that the evolution of halo concentration has two primary modes: (1) smooth increase due to pseudo-evolution; and (2) intense responses to physical merger events. Mer…
The relative roles of mergers and star formation in regulating galaxy growth are still a matter of intense debate. We here present our DECODE, a new Discrete statistical sEmi-empiriCal mODEl specifically designed to predict rapidly and efficiently, in a full cosmological context, galaxy assembly and merger histories for any given input stellar mass-halo mass (SMHM) relation. DECODE generates object-by-object dark matter merger trees (hence discrete) from accurate subhalo mass and infall redshift probability functions (hence statistical) for all subhaloes, including those residing within other …
Theoretical models are vital for exploring the galaxy merger process, which plays a crucial role in the evolution of galaxies. Recent advances in modelling have placed tight constraints on the buildup of stellar material in galaxies across cosmic time. Despite these successes, extracting the merger rates from observable data remains a challenge. Differences in modelling techniques, combined with limited observational data, drive conflicting conclusions on the merging timescales of close pairs. We employ an empirical model for galaxy formation that links galaxy properties to the growth of simul…
Galaxy mergers trigger both star formation and accretion onto the central supermassive black hole. As a result of subsequent energetic feedback processes, it has long been proposed that star formation may be promptly extinguished in galaxy merger remnants. However, this prediction of widespread, rapid quenching in late stage mergers has been recently called into question with modern simulations and has never been tested observationally. Here we perform the first empirical assessment of the long-predicted end phase in the merger sequence. Based on a sample of ~500 post-mergers identified from t…
Non-parametric Morphologies of Mergers in the Illustris Simulation
我们研究的非参数形态的合并事件在宇宙学的背景下，使用的Illustris项目。我们产生模拟G-波段的图像相比，从公开的插图模拟理想化的模拟图像在$z=0$的观测调查。然后，我们测量非参数指标：不对称性，基尼系数，$M_{20}$，块状和浓度的一组星系与$M_* >10^{10}$ M $_\odot$。我们将这些自动统计数据与星系最近的合并历史和密切同伴的存在相关联。我们的主要贡献是评估在宇宙学框架，经验得出的非参数分界线和平均时间尺度，用于确定合并率观测。我们发现，在分界线以上的星系中，98%都有一个亲密的伴星，或者最近经历了一次合并事件。平均而言，从$G-M_{20}$标准中获得的合并签名与到最后一次合并事件的过去时间明显相关。我们还发现，这种不对称性与星系对的分离和相对速度有关，对分离为$d < 50$ h $^{-1}$ kpc和相对速度为$V < 350$ km s $^{-1}$的系统，这种不对称性增强较大.我们发现，$G-M_{20}$是最敏感的最近的合并（$\sim0.14$陀螺仪）和正在进行的合并与恒星质量比大于0.1。对于这个指标，我们计算合并的平均观测时间尺度的$\sim0.2$陀螺仪，与以前的结果一致，并表明，形态学推导的合并率恢复固有的总合并率的模拟和合并率作为恒星质量的函数。
We present a study of galaxy mergers up to $z=10$ using the Planck Millennium cosmological dark matter simulation and the {\tt GALFORM} semi-analytical model of galaxy formation. Utilising the full ($800$ Mpc)$^3$ volume of the simulation, we studied the statistics of galaxy mergers in terms of merger rates and close pair fractions. We predict that merger rates begin to drop rapidly for high-mass galaxies ($M_*>10^{11.3}-10^{10.5}$ $M_\odot$ for $z=0-4$), as a result of the exponential decline in the galaxy stellar mass function. The predicted merger rates increase and then turn over with incr…
We introduce and apply a new approach to probe the response of galactic stellar haloes to the interplay between cosmological merger histories and galaxy formation physics. We perform dark matter-only, zoomed simulations of two Milky Way-mass hosts and make targeted, controlled changes to their cosmological histories using the genetic modification technique. Populating each history's stellar halo with a semi-empirical, particle tagging approach then enables a controlled study, with all instances converging to the same large-scale structure, dynamical and stellar mass at $z=0$ as their reference…
Unveiling the (in)consistencies among the galaxy stellar mass function, star formation histories, satellite abundances and intracluster light from a semi-empirical perspective
In our hierarchical structure-formation paradigm, the observed morphological evolution of massive galaxies -- from rotationally-supported discs to dispersion-dominated spheroids -- is largely explained via galaxy merging. However, since mergers are likely to destroy discs, and the most massive galaxies have the richest merger histories, it is surprising that any discs exist at all at the highest stellar masses. Recent theoretical work by our group has used a cosmological, hydrodynamical simulation to suggest that extremely massive (M* > 10^11.4 MSun) discs form primarily via minor mergers betw…
We investigate whether the considerable diversity in the satellite populations of nearby Milky Way (MW)-mass galaxies is connected with the diversity in their host's merger histories. Analyzing 8 nearby galaxies with extensive observations of their satellite populations and stellar halos, we characterize each galaxy's merger history using the metric of its most dominant merger, $M_{\rm \star,Dom}$, defined as the greater of either its total accreted stellar mass or most massive current satellite. We find an unexpectedly tight relationship between these galaxies' number of $M_{V}\,{<}\,{-}9$ sa…
VINTERGATAN-GM: long-lived satellite planes induced by a massive GSE-like merger
Universidad Complutense de Madrid（马德里康普顿斯大学）；Lund University（隆德大学）；University of Surrey（萨里大学）；Durham University（杜伦大学）；University of Bath（巴斯大学）；Universidad Autónoma de Madrid（马德里自治大学）
Habitability of galaxies and application of merger trees in astrobiology
星系是我们宇宙中物质的主要组织形式。因此，它们对于天体生物学的新的多学科领域具有明显的兴趣。特别是，研究星系的可居住性是理论和数值天体生物学的主要挑战之一。然而，它的理论基础往往是混乱和模糊的。在这里，我们提出了一个系统的尝试，列出和分类的主要因果因素发挥作用的紧急星系的可居住性。此外，我们认为，宇宙合并树的方法是特别有用的，在描绘什么是系统的和合法的天体生物学性质的星系在目前的时代与那些是历史偶然性的产物，特别是与更广泛的河外环境的相互作用。采用从宇宙学N体模拟中提取的合并树作为天体生物学的一种新的和有前途的研究方法，由Stanway et al.（2018）开创。我们分析了合并树的适用性的一般问题，并提出了初步的结果，一组从Illustris项目中提取的树。在某种意义上，这种方法是直接补充使用大规模宇宙学模拟研究宜居带的单个星系与高质量/空间分辨率;一起，他们开创了一个新的时代的协同作用和宇宙学和天体生物学之间的综合。
Dynamical friction (DF) against stars and gas is thought to be an important mechanism for orbital evolution of massive black holes (MBHs) in merger remnant galaxies. Recent theoretical investigations however show that DF does not always lead to MBH inspiral. For MBHs evolving in gas-rich backgrounds, the ionizing radiation that emerges from the innermost parts of their accretion flow can affect the surrounding gas in such a way to cause the MBHs to accelerate and gain orbital energy. This effect was dubbed "negative DF". We use a semi-analytic model to study the impact of negative DF on pairs …
