A search for fossil groups in the Sloan Digital Sky Survey was performed using virtual observatory tools. A cross-match of the positions of all SDSS luminous red galaxies (with r 19 and measured spectroscopic redshifts) with sources in the ROSAT All-Sky Survey catalog resulted in a list of elliptical galaxies with extended X-ray emission (with a galaxy/ROSAT-source distance of less than 0.5' in all cases). A search for neighbors of the selected elliptical galaxies within a radius of 0.5 h Mpc was conducted, taking into account the r-band magnitudes and spectroscopic or photometric redshifts of all objects within this area, leading to a sample of 34 candidate fossil groups. Considering this sample, the estimated space density of fossil systems is n = (1.0 ± 0.6) × 10-6 h Mpc-3.
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机译：使用虚拟天文台工具在Sloan Digital Sky Survey中搜索了化石群。所有SDSS发光红色星系（r <19且测量的光谱红移）的位置与ROSAT All-Sky Survey目录中的源交叉匹配，得出了具有扩展X射线发射的椭圆星系列表（带有星系） / ROSAT源距离在所有情况下均小于0.5'。考虑到r波段的大小以及该区域内所有物体的光谱或光度红移，在0.5 h Mpc半径内搜索选定的椭圆星系的邻居，从而得出了34个候选化石组的样本。考虑到该样本，化石系统的估计空间密度为n =（1.0±0.6）×10-6 h Mpc-3。
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