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Register a new userMassive relic galaxies prefer dense environments
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Added by
Luis Peralta de Arriba
Publication date
2016
fields
Physics
and research's language is
English
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We study the preferred environments of $z sim 0$ massive relic galaxies ($M_star gtrsim 10^{10}~mathrm{M_odot}$ galaxies with little or no growth from star formation or mergers since $z sim 2$). Significantly, we carry out our analysis on both a large cosmological simulation and an observed galaxy catalogue. Working on the Millennium I-WMAP7 simulation we show that the fraction of today massive objects which have grown less than 10 per cent in mass since $z sim 2$ is ~0.04 per cent for the whole massive galaxy population with $M_star > 10^{10}~mathrm{M_odot}$. This fraction rises to ~0.18 per cent in galaxy clusters, confirming that clusters help massive galaxies remain unaltered. Simulations also show that massive relic galaxies tend to be closer to cluster centres than other massive galaxies. Using the New York University Value-Added Galaxy Catalogue, and defining relics as $M_star gtrsim 10^{10}~mathrm{M_odot}$ early-type galaxies with colours compatible with single-stellar population ages older than 10 Gyr, and which occupy the bottom 5-percentile in the stellar mass-size distribution, we find $1.11 pm 0.05$ per cent of relics among massive galaxies. This fraction rises to $2.4 pm 0.4$ per cent in high-density environments. Our findings point in the same direction as the works by Poggianti et al. and Stringer et al. Our results may reflect the fact that the cores of the clusters are created very early on, hence the centres host the first cluster members. Near the centres, high-velocity dispersions and harassment help cluster core members avoid the growth of an accreted stellar envelope via mergers, while a hot intracluster medium prevents cold gas from reaching the galaxies, inhibiting star formation.
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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 most massive galaxies with $M_mathrm{star}ge10^{11.6},M_{odot}$, which are commonly found in dense environments, like galaxy clusters. Therefore, one can expect that there is a close connection between active EMBHs and dense environments. Here, we study the environments of 9461 galaxies and 2943 quasars at $0.24 le z le 0.40$, among which 52 are extremely massive quasars with $log(M_mathrm{BH}/M_{odot}) ge 9.4$, using Sloan Digital Sky Survey and MMT Hectospec data. We find that, on average, both massive quasars and massive galaxies reside in environments more than $sim2$ times as dense as those of their less massive counterparts with $log(M_mathrm{BH}/M_{odot}) le 9.0$. However, massive quasars reside in environments about half as dense as inactive galaxies with $log(M_mathrm{BH}/M_{odot}) ge 9.4$, and only about one third of massive quasars are found in galaxy clusters, while about two thirds of massive galaxies reside in such clusters. This indicates that massive galaxies are a much better signpost for galaxy clusters than massive quasars. The prevalence of massive quasars in moderate to low density environments is puzzling, considering that several simulation results show that these quasars appear to prefer dense environments. Several possible reasons for this discrepancy are discussed, although further investigation is needed to obtain a definite explanation.
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