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Black hole mass scaling relations suggest that extremely massive black holes(EMBHs) with $M_\mathrm{BH}\ge10^{9.4}\,M_{\odot}$ are found in the mostmassive galaxies with $M_\mathrm{star}\ge10^{11.6}\,M_{\odot}$, which arecommonly found in dense environments, like galaxy clusters. Therefore, one canexpect that there is a close connection between active EMBHs and denseenvironments. Here, we study the environments of 9461 galaxies and 2943 quasarsat $0.24 \le z \le 0.40$, among which 52 are extremely massive quasars with$\log(M_\mathrm{BH}/M_{\odot}) \ge 9.4$, using Sloan Digital Sky Survey and MMTHectospec data. We find that, on average, both massive quasars and massivegalaxies reside in environments more than $\sim2$ times as dense as those oftheir less massive counterparts with $\log(M_\mathrm{BH}/M_{\odot}) \le 9.0$.However, massive quasars reside in environments about half as dense as inactivegalaxies with $\log(M_\mathrm{BH}/M_{\odot}) \ge 9.4$, and only about one thirdof massive quasars are found in galaxy clusters, while about two thirds ofmassive galaxies reside in such clusters. This indicates that massive galaxiesare a much better signpost for galaxy clusters than massive quasars. Theprevalence of massive quasars in moderate to low density environments ispuzzling, considering that several simulation results show that these quasarsappear to prefer dense environments. Several possible reasons for thisdiscrepancy are discussed, although further investigation is needed to obtain adefinite explanation.

astrophysical journal/the astrophysical journal

Extremely Massive Quasars are not Good Proxies for Dense Environments  Compared to Massive Galaxies: Environments of Extremely Massive Quasars and  Galaxies