A rich, nearby galaxy cluster in Sagittarius

Creators: Djorgovski, S.; Thompson, D. J.; de Carvalho, R. R.; Mould, J. R.

Abstract

We report on the existence of a rich, heavily obscured galaxy cluster (or a set of clusters) in Sagittarius, centered near l_(II) ≃ 359°, b_(II) ≃ 8°. About 30 objects, originally identified by Terzan and his collaborators, were imaged and followed up spectroscopically. We present here redshifts for 21 galaxies found among them. There is a pronounced concentration at cz ≃ 8600 km/s (containing 14 out of the 21 galaxies), and another possible concentration near cz ≃ 11 340 km/s (five out of 21). This putative Sagittarius cluster is probably part of a larger system, involving the Ophiuchus cluster at l_(II) ≃ 1°, b_(II) ≃ 9°, cz ≃ 8400 km/s, previously identified by Johnston et al. and Wakamatsu and Malkan. The heavy extinction on this line of sight (we estimate A_v ~ 5^m from the observed Balmer decrements) suggests that there is a much larger, as yet undetected number of galaxies in this direction. We propose that the Sagittarius-Ophiuchus concentration may be a massive cluster, or even a supercluster, comparable in richness to the Coma-A 1367 system, and at a comparable distance. The existence of this concentration serves as a reminder that some possibly dynamically important constituents of the local large-scale structure may be absent from the galaxy .catalogs available now, and the dynamical analyses based on them.

Additional Information

© 1990 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 20 March 1990; revised 5 June 1990. Based in part on the observations made at Las Campanas Observatory, as a part of a collaborative agreement between the California Institute of Technology and the Carnegie Institution of Washington. We would like to thank the staff of Cerro Tololo and Las Campanas Observatories for their help during our observing runs, and to S. Morris and S. Anderson for obtaining the spectrum of TJ8. The paper benefited from the constructive criticism by Matt Malkan, the referee. This work was supported in part by the Alfred P. Sloan Foundation and by California Institute of Technology (S.D.), NSF Grant No. AST 87-21705 (J.R.M.), and by a Kingsley fellowship (D.J.T.) R.R.dC. is on leave of absence from Observatorio Nacional, CNPq, Rio de Janeiro, Brazil.

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Published - 1990AJ____100__599D.pdf

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