Evolution of splashback boundaries and gaseous outskirts: insights from mergers of self-similar galaxy clusters
Evolution of splashback boundaries and gaseous outskirts: insights from mergers of self-similar galaxy clusters
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DOI：
10.1093/mnras/stab1546
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发表时间：
2021-03
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通讯作者：
Congyao Zhang;I. Zhuravleva;A. Kravtsov;E. Churazov
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作者：
Congyao Zhang;I. Zhuravleva;A. Kravtsov;E. Churazov
一个自相似的球形坍缩模型预测了星系团外围的暗物质（DM）溅射和吸积冲击，但忽略了结构形成的一个关键因素——与合并相关的过程。为了填补这一空白，我们进行了自相似星团合并的模拟，并在理想的宇宙学背景下研究了它们的DM和气体演化。我们的模拟结果表明，在大合并过程中，星系团迅速收缩，溅射半径rsp减小，接近虚拟半径rvir。虽然rsp与自相似模型中的平滑质量吸积率（MAR）参数Γs相关，但我们的模拟显示了与总MAR相似的趋势Γvir（包括合并和Γs）。Γvir−rsp/rvir关系的散点表明，在宇宙学模拟中，星系团的Γs ~ 1一般较低。与DM相反，当失控的合并激波超过外部吸积激波时，合并加速激波（MA-）形成的热气体大气显著膨胀。在重大合并后，对于Γs， ma冲击半径比rsp大1.7倍。1，是Γs和3的~ RSP。这意味着(1)合并可以很容易地产生宇宙学模拟中测量到的ma激波溅射偏移，(2)平滑的MAR在远离ma激波驻留的细丝的区域很小。我们进一步讨论了在合并的不同时期形成的各种冲击和接触不连续，星团外围的冲压压力剥离，以及成员星系的溅射特征对其轨道参数的依赖。
A self-similar spherical collapse model predicts a dark matter (DM) splashback and accretion shock in the outskirts of galaxy clusters while misses a key ingredient of structure formation – processes associated with mergers. To fill this gap, we perform simulations of merging self-similar clusters and investigate their DM and gas evolution in an idealized cosmological context. Our simulations show that the cluster rapidly contracts during the major merger and the splashback radius rsp decreases, approaching the virial radius rvir. While rsp correlates with a smooth mass accretion rate (MAR) parameter Γs in the self-similar model, our simulations show a similar trend with the total MAR Γvir (includes both mergers and Γs). The scatter of the Γvir − rsp/rvir relation indicates a generally low Γs ∼ 1 in clusters in cosmological simulations. In contrast to the DM, the hot gaseous atmospheres significantly expand by the merger-accelerated (MA-) shocks formed when the runaway merger shocks overtake the outer accretion shock. After a major merger, the MA-shock radius is larger than rsp by a factor of up to ∼ 1.7 for Γs . 1 and is ∼ rsp for Γs & 3. This implies that (1) mergers could easily generate the MA-shock-splashback offset measured in cosmological simulations, and (2) the smooth MAR is small in regions away from filaments where MA-shocks reside. We further discuss various shocks and contact discontinuities formed at different epochs of the merger, the ram pressure stripping in cluster outskirts, and the dependence of member galaxies’ splashback feature on their orbital parameters.