A Cluster or Filament of Galaxies at Redshift Z=2.5

Abstract

We report the discovery of 56 new Lyman-alpha-emitting candidates (LECs) at redshift z=2.5 in a field of 8'x14' around two previously known weak radio QSOs and a cosmic microwave background decrement (CMBD) that is plausibly due to the Sunyaev-Zel'dovich effect. Broad-band and medium-band imaging at the redshifted Lyman-alpha wavelength have allowed us to identify the LECs at the redshift of the QSOs. Three of the brightest LECs have been confirmed spectroscopically, with redshifts between z=2.501 and z=2.557; one of them is another QSO. Excluding the third QSO, the four spectroscopically confirmed objects form a 3' filament with a rest-frame velocity dispersion of 1000 km/s lying adjacent to the CMBD, and there is a significant concentration of LECs at the NW end of the filament around the brightest QSO. If confirmed, a velocity dispersion ~1000 km/s on a proper scale ~1 Mpc at redshift z=2.5 would, in and of itself, constrain the cosmological model to low Omega.

Submitted to Astrophysical Journal Letters February 17, 1998; Accepted November 19, 1998. The new version includes minor changes following referee comments. 10 LaTeX pages and Figures 2-4. Figure 1 (1.7 MB) is available at ftp://sbast4.ess.sunysb.edu/pub/ayahil/papers/sz_cluster_fig1.ps.gz The entire paper in ApJ emulating format (1.9 MB) is available at ftp://sbast4.ess.sunysb.edu/pub/ayahil/papers/sz_cluster_apj.ps.gz

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