To investigate the dependence of the occurrence of active galactic nuclei (AGNs) on local galaxy density, we study the nuclear properties of ~5000 galaxies in the Coma Supercluster whose density spans 2 orders of magnitude from the sparse filaments to the cores of the rich clusters. We obtained optical spectra of the nuclei of 177 galaxies using the 1.5m Cassini telescope, which are added to the 4785 spectra available from SDSS (DR7) to fill-in the incomplete coverage by SDSS of luminous galaxies. We perform a spectral classification of the nuclei of galaxies (with a completeness of 98% at r<17.77), classifying the nuclear spectra in six classes: three of them (SEY, sAGN, LIN) refer to AGNs and the remaining three (HII, RET, PAS) refer to different stages of starburst activity. To perform such classification, we use the WHAN diagnostic, after correcting Halpha by 1.3 A for underlying absorption. We find that 482 (10%) of 5027 galaxies host an AGN: their frequency strongly increases with increasing luminosity of the parent galaxies, such that 32% of galaxies with Log(i-Lum)<10.2 (Solar) harbor an AGN at their interior. In addition to their presence in luminous galaxies, AGNs are also found in red galaxies with <g-i> < 1.15 \pm 0.15 mag. The majority of SEY and sAGN (strong AGNs) are associated with luminous late-type (or S0a) galaxies, while LIN (weak AGNs) and RET ("retired"), are mostly found among E/S0as. The number density of AGNs, HII region-like, and retired galaxies is found to anti-correlate with the local density of galaxies, such that their frequency drops by a factor of two near the cluster cores, while the frequency of galaxies containing passive nuclei increases by the same amount towards the center of rich clusters. The dependence of AGN number density on the local galaxy density is greater than the one implied by morphology segregation alone.
The evolution of dwarf galaxies in the Coma supercluster
利用SDSS DR 7在500平方度区域的分光光度数据，研究后发座超星系团（z=0.023）中矮星系（~M*+2<M_z<M*+4）的演化。我们发现，在后发座超星系团中，红矮星主要集中在后发座和阿贝尔1367星系团的致密核心，以及嵌入连接它们的灯丝中的星系群中。然而，在后发座星系团和Abell 1367星系团的陷落区发现了后星爆（k+A）矮星，偶尔也在沿暗条嵌入的星系群中发现，这表明深势阱附近普遍存在的强速度场可能与导致矮星系后星爆阶段的机制密切相关。此外，后发座星系团中一些k+A矮星的蓝色，在其维里半径内发现，这表明这些星系中的恒星形成在过去的500 Myr中非常迅速地熄灭了。超星系团中60%以上的红矮星系的H_δ吸收角为0-3角，这表明在这些星系中有一个不可忽略的部分发生了一个主要的恒星形成事件，在最后一个Gyr内结束，使它们能够移动到红色序列。后发座超星系团中的蓝矮星系在EW（H_α）-EW（H_δ）平面上呈双峰分布，其中一个星系团在H_α中有很高的发射，在H_δ中也有一些发射。在EW（H_α）-EW（H_δ）平面上，蓝矮星和红矮星的一个子群重合，在H_δ上表现出吸收，在H_α上表现出相对较低的发射。我们认为，后者人口的很大一部分是被动矮星系的祖先，大量发现在低红移丰富的集群，如后发座的核心。
The eROSITA Final Equatorial-Depth Survey (eFEDS): A complete census of X-ray properties of Subaru Hyper Suprime-Cam weak lensing shear-selected clusters in the eFEDS footprint
