Intergalactic Hydrogen in the Virgo Cluster.

Abstract

A fixed horn antenna having a 100 x 100 beam and a switched load radiometer with a maser preamplifier was used to observe the 21-cm spectrum of the Virgo Cluster of galaxies. An upper limit to the antenna temperature is 0.0240K relative to regions outside the cluster with filters of 2 ThIc/sec width. If the excitation temperature of the intergalactic hydrogen is sufficiently greater than the background continuum radiation that absorption can be ignored, and if the velocity spectrum is that defined by the galaxies, the density of optically thin neutral hydrogen in the cluster does not exceed that outside the cluster by an amount that gives 5.6x 1012 solar masses in the cluster. For comparison, HoImberg has obtained 3.1 x 1013 solar masses for the galaxies in the cluster.

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