Large-scale structure of galaxies in the Ophiuchus region |
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Authors: | Takashi Hasegawa † Ken-ichi Wakamatsu ‡ Matthew Malkan ‡ Kazuhiro Sekiguchi John W Menzies Quentin A Parker Jun Jugaku Hiroshi Karoji Sadanori Okamura |
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Institution: | Gunma Astronomical Observatory, 6860-86, Nakayama, Takayama, Agatsuma, Gunma 377-0802, Japan;Kiso Observatory, Institute of Astronomy, The University of Tokyo, Kiso, Nagano 397-01, Japan;Department of Astronomy, School of Science, The University of Tokyo, Bunkyo, Tokyo 113, Japan;Physics Department, Gifu University, Gifu 501-1193, Japan;Department of Astronomy, UCLA, Los Angeles, CA 90024, USA;Subaru Project Office, National Astronomical Observatory of Japan, Mitaka, Tokyo 181, Japan;South African Astronomical Observatory, PO Box 9, Observatory 7935, Cape, South Africa;Anglo-Australian Observatory, PO Box 296, Epping, NSW 2121, Australia;Research Institute of Civilization, Tokai University, Hiratsuka, Kanagawa 259-12, Japan |
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Abstract: | The large-scale structure around the Ophiuchus cluster of galaxies in the vicinity of the Galactic Centre ( l =0 5, b =9 5, cz =8500 km s?1) is investigated on the basis of a galaxy survey and spectroscopic observations made for a 12°×17° area. The galaxy survey was performed using six ESO/SERC Sky Survey Atlas films, and 4021 galaxies were detected in total. Recession velocities were newly obtained for 179 galaxies to make the total number of galaxies in the survey area with known velocities 219. In the distribution of bright galaxies, we identified seven new clumps of galaxies. Comparing the surface number density of bright galaxies with the Galactic extinction, which is estimated from the 100‐μm flux density in the IRAS Sky Survey Atlas, we demonstrate that the seven clumps are not spurious as a result of the inhomogeneity of the Galactic extinction. Among the seven clumps, two are found to be clusters and four to be groups on the basis of the histogram of recession velocities and the number of member galaxies. The Ophiuchus cluster, two newly identified clusters, and four groups are all concentrated at 9000 km s?1. Field galaxies are also distributed centred at 8500 km s?1. Hence field galaxies occupy a common three-dimensional region with galaxies in the clusters and groups, and altogether they form a large-scale structure of supercluster size. As opposed to the overdensity in the supercluster region, the mean number density of galaxies in the velocity range 0–5000 km s?1 is only 25 per cent of the mean number density of the Universe, comparable with the density of the well-known Böotes void. Hence this nearby three-dimensional region in Ophiuchus is a void of galaxies also. |
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Keywords: | dust extinction galaxies: clusters: individual: the Ophiuchus cluster large-scale structure of Universe |
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