AI 中文总结
研究\(z \approx 4.5\)时大质量星系合并对银河系质量星系前身恒星形态的影响，用AGORA九个先进代码分析，发现反馈类型影响遗迹形态，遗迹盘方向与代码无关，还与模型比较，表明合并遗迹形态可作恒星反馈过程的有力探针。
AI 中文摘要
星系合并对初始条件高度敏感，为星系模拟代码的比较研究提供了有价值的背景。继第一篇关注合并驱动恒星形成的论文之后，本文进行了代码比较，研究了在红移\(z \approx 4.5\)时大质量星系合并对银河系质量星系前身的形态转变影响。分析采用了AGORA CosmoRun宇宙学放大模拟套件中的九个先进代码。结果表明，采用的恒星反馈类型会影响星系的致密化和恒星盘形成。纯热反馈的代码产生的合并遗迹在合并期间和之后形成盘并变得致密；包含动力学反馈的代码在第一次近心点附近开始形成盘并致密化；具有强延迟冷却或超气泡反馈的代码抑制盘形成并产生更扩展的遗迹。遗迹盘的方向与代码无关。所有代码中，遗迹盘的旋转角动量与相互作用的轨道角动量对齐，而非合并前的旋转轴。与圣克鲁斯半解析模型的比较表明，在恒星质量和半质量半径方面有合理的一致性，但该模型在显示强致密化（膨胀）的代码中低估（高估）了暗物质分数和速度弥散。遗迹形态对反馈方案的系统依赖性表明，合并遗迹形态可作为恒星反馈过程的有力探针。
英文摘要
Galaxy mergers, with their high sensitivity to initial conditions, provide a valuable setting for comparative studies of galaxy simulation codes. Following our first paper focusing on merger-driven star formation, we present a code comparison examining the morphological transformation impact of a major galaxy merger at $z \approx 4.5$ on a Milky Way-mass galaxy progenitor. Our analysis employs nine state-of-the-art codes from the AGORA CosmoRun cosmological zoom-in simulation suite. For this merger, we show that the adopted stellar feedback type influences the galaxy's compaction and stellar disc formation. Codes with purely thermal feedback produce a merger remnant that forms a disc and becomes compact primarily during and after coalescence; codes that include kinetic feedback begin disc formation and compaction around the first periapsis; and codes with strong delayed cooling or superbubble feedback suppress disc formation and produce a more extended remnant. In contrast, the orientation of the remnant disc is code-independent. In all codes, the rotational angular momentum of the remnant disc aligns with the interaction's orbital angular momentum rather than the pre-merger rotational axis, implying that the infalling gas preserves its orbital angular momentum to form a new disc. Comparisons with the Santa Cruz semi-analytic model show reasonable agreement in stellar mass and half-mass radius, yet the model underpredicts (overpredicts) the dark matter fraction and velocity dispersion for codes exhibiting strong compaction (expansion). The systematic dependence of our remnants' morphology on feedback schemes demonstrates that merger remnant morphology may serve as a powerful probe of stellar feedback processes.
Comments24 pages (20 pages main text plus appendices and references), 10 figures (8 in main text), 3 tables, submitted to MNRAS. Visit the AGORA Collaboration website (https://sites.google.com/site/santacruzcomparisonproject/) for more information
