论文标题
大调查-III。宇宙中午的超质量被动星系的环境：通过合并生长的BCG祖细胞
LARgE Survey -- III. Environments of Ultra-Massive Passive Galaxies at Cosmic Noon: BCG progenitors growing through mergers
论文作者
论文摘要
我们研究了61个极为罕见的Z〜1.6超质量的被动性星系（UMPEGS：恒星质量m_stars> 10^11.5 m_sun）的样品的环境，该环境基于Cheema等人在Cheema等人中提出的聚类分析。 （2020） - 似乎与非常庞大的（M_halo〜10^14.1 H^-1 m_sun）暗物质光环有关，这些黑物质可能是Z〜0大量（coma-和处女座状的）星系簇的祖细胞。我们发现，UMPEG平均具有质量比M_SAT的卫星星系少于一个卫星星系：M_UMPEG> 〜1：5（即M_SAT> 〜10^10.8 m_sun）在0.5 MPC内；我们在典型的UMPEG及其最大的卫星之间观察到的巨大质量间隙意味着Z〜1.6 UMPEG通过主要合并组装而成。使用文献中观察到的卫星计数与合并时标，我们估计质量比> 〜1：4的合并估计为〜13％gyr^-1（具有〜2x系统的不确定性）。这种相对较低的生长速率不太可能显着影响恒星质量功能的巨大末端的形状，而恒星质量功能的大量末端必须由新的超质量星形星系的新同类群的淬火驱动。但是，这种增长速率足够高，以至于典型的Z〜1.6 m_umpeg = 10^11.6 m_sun Umpeg可以生长成〜10^12 m_sun最明亮的群集星系（BCG）。我们的观察结果有利于一种场景，即我们的UMPEG是当今BCG的主要分支祖细胞，这些祖先首先通过高红移的主要合并组装，并在后来的时间（可能是次要）合并。
We study the environments of a sample of 61 extremely rare z~1.6 Ultra-Massive Passively Evolving Galaxies (UMPEGs: stellar masses M_stars >10^11.5 M_sun) which -- based on clustering analysis presented in Cheema et al. (2020) -- appear to be associated with very massive (M_halo ~ 10^14.1 h^-1 M_sun) dark matter halos that are likely to be the progenitors of z~0 massive (Coma- and Virgo-like) galaxy clusters. We find that UMPEGs on average have fewer than one satellite galaxy with mass ratio M_sat : M_UMPEG >~ 1:5 (i.e., M_sat >~ 10^10.8 M_sun) within 0.5 Mpc; the large mass gap that we observe between the typical UMPEG and its most massive satellite implies that the z~1.6 UMPEGs assembled through major mergers. Using observed satellite counts with merger timescales from the literature, we estimate the growth rate due to mergers with mass ratio of >~ 1:4 to be ~13% Gyr^-1 (with a ~2x systematic uncertainty). This relatively low growth rate is unlikely to significantly affect the shape of the massive end of the stellar mass function, whose evolution must instead be driven by the quenching of new cohorts of ultra-massive star-forming galaxies. However, this growth rate is high enough that, if sustained to z~0, the typical z~1.6 M_UMPEG=10^11.6 M_sun UMPEG can grow into a M_stars~10^12 M_sun brightest cluster galaxy (BCG) of a present-day massive galaxy cluster. Our observations favour a scenario in which our UMPEGs are main-branch progenitors of some of the present-day BCGs that have first assembled through major mergers at high redshifts and grown further through (likely minor) merging at later times.
