Previous
abstract 
Next
abstract
Session 53 - Surveys of Galaxies & Clusters.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
Between recombination (z \approx 1100) and the quasars (z \approx 5) structures formed which today we observe in the hierarchy of galaxies, clusters, voids, and sheets. Theories of what happened in that interval are constrained by observations of the diffuse CMB and the appearance of discrete objects. We want to extend the lower bound by detecting protoclusters in collapse. We are trying to observe these in the hydrogen hyperfine line (\lambda 21 cm), at redshifts 4.7 \leq z \leq 5.5. The expected signal is very weak. In order to make a detection in a reasonable time we require the large collecting area of the Arecibo Observatory. Our experiment, installed in the summer of 1994, runs continuously and in the main independently of scheduled observations and the observatory upgrade. Dual broadband point feeds are mounted on the telescope cat-walk where it intersects the focal surface, allowing continuous transit observations. The dedicated receiver includes low-noise preamplifiers, RF and IF filters and mixers, and a custom power-accumulating FFT spectrometer with 10 kHz resolution and 32 MHz instantaneous bandwidth centered at 235 MHz (4 k channels per feed). The spectrometer output is time tagged and logged to disk on a control PC, and digital audio data tapes are shipped biweekly to Cambridge. We present the current status of the experiment. Strong RFI is a problem except for a few early morning hours, and spillover losses are unexpectedly high. We are redesigning our feed to lower horizon sensitivity and maximize overall SNR. Design requirements are derived by modeling with candidate feeds the effects of spherical aberration and squint on system gain and noise temperature.
