STScI Preprint #1250

An Arecibo Search for Broad 21 cm Lines of Atomic Hydrogen in Clusters of Galaxies

We present the results of sensitive observations of the inner 3.'3 (~100 kpc) of 21 clusters of galaxies with the Arecibo telescope utilizing the autocorrelation spectrometer in complex sampling mode to obtain a total bandwidth of 40 MHz, corresponding to a velocity coverage of ~7000-8000 km  s^-1. These are the most sensitive observations capable of detecting HI with line widths expected for gas in the ICM. We did not detect any significant emission features with 500  FWHM  4000 km s^-1 through the centers of these clusters.

Limits on optically thin HI from 'narrow' galaxy-type features are typically ~5×10⁸ M ; while from broad band cluster-type features they are about an order of magnitude higher. We derive constraints on the covering factor of any optically thick HI within the Arecibo beam. We obtain upper limits c_f ~ 3 × 10^-3 assuming that the temperature of the HI is 10 K.

This corresponds to a limited range of parameter space for the clouds in which the cloud temperature is typically less than a few tens of K and the number of clouds along the line of sight is less than a few tens of clouds. Cloud temperatures this low are probably inconsistent with cloud heating due to X-rays from the ICM, however, this is uncertain. The very small range of parameter space which is allowed by the observations makes it unlikely that there is very much atomic hydrogen in the ICM of these clusters.

Status:

Appeared in: The Astronomical journal, 116:623-633, 1998

Affiliations:

¹) Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218, USA
²) University of Michigan