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Session 87 -- Cluster Evolution

Display presentation, Friday, January 14, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[87.02] A Cluster of Galaxies at Redshift z=3.4?

We report the likely detection of a cluster of 16 radio-quiet galaxies at redshift $z=3.4$, identified in the field around the optically thick absorption system toward Q0000-263 at $z_{abs}=3.390$. Two of these galaxies, a Ly$\alpha$ emitter at $z_{em}=3.428$ and the one responsible for the absorption system, have redshifts spectroscopically confirmed. The other 14 galaxies have been identified with a multi--color imaging technique that makes use of passbands ($U_n$, $G$ and ${\cal R}$ properly designed to detect sources in the redshift interval $3 This results seems to confirm the previous detection of galaxy clustering around high-redshift optically-thick absorption systems. If this is a general property, our technique of following up multicolor imaging with correlation analysis will be highly efficient in isolating high-redshfit clusters. It is expected that the direct observation of young structures at very high redshift ($z>1$) will discriminate between the two competing scenarios for the formation of the large-scale structure, generically referred to as ``top-down'' and ``bottom--up'' models.

In addition, for the first time, a significant number of high-redshift radio-quiet galaxies is available for establishing the general properties of young, normal galaxies. Their rest-frame UV SED is very blue, basically consistent with a flat spectrum (after accounting for Lyman $\alpha$ forest blanketing), which is typical of star--forming galaxies. The SFRs measured from the continuum luminosity range between 30 and 100 M$_{\odot}$y$^{-1}$.

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