Limits on the space density of low mass HI clouds at the present epoch

Details Limits on the space density of low mass HI clouds at the present epoch Limits on the space density of low mass HI clouds at the present epoch

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.4917s&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #49.17; Bulletin of the American Astronomical Society, Vol. 24, p.811

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A number of neutral-hydrogen-rich extragalactic objects have recently been discovered by chance in the observations that were designed for other purposes. Although to date, no free-floating, invisible, intergalactic HI cloud has been discovered, there have been few sensitive surveys designed specifically to search for tiny clouds at the low mass end of the distribution. In this study, we present a method to look for HI clouds in a blind survey using the Arecibo Telescope. The technique may be especially effective at times during the Arecibo Upgrade when the telecope will have no ability to track. To maximize the sensitivity and to avoid the problems of changing gain with different zenith angle, we locked the Arecibo azimuthal and zenith angle to constant values near the zenith. The observations are highly efficient since as the earth turns, spectra are acquired continuously. Integration time for each survey point accumulates since the beam retraces the same path through the sky on successive days. The repetitive sky coverage makes the survey immune to radio interference and unstable spectral baselines since these types of errors are readily identified and filtered out during the data processing. The spectra are most easily analyzed by loading each days' observation into an 2-D image (frequency and time axes) in IRAF and then using the built-in averaging, smoothing and filtering tasks. The spectrometer covered the redshift range 200 to 4500 km s(-1) with spectral resolution of 8 km s(-1) . The observations are sensitive to HI masses of 10(6) Msun at a distance of 7 Mpc and 10(8) Msun at the full depth of the survey.

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