Hydrogen Hyperfine Studies of the Early Universe

Abstract

The Arecibo Search for HI Protoclusters is an ongoing experiment at
Arecibo Observatory to detect highly redshifted hyperfine emission
from protogalactic condensates of neutral hydrogen. I describe the
custom-built instrument we have installed, and the reduction and
analysis of the data obtained. I am able to place upper limits on the
masses of Hi protoclusters undetected in our fields, generally at the
level 10¹⁶ solar masses. I discuss the instrumental and
environmental effects which most in uence our sensitivity. I also
describe extensive numerical modeling of the system optics aimed at
maximizing sensitivity.

The MIT Near--Real--Time Correlator is a test fixture in support of
the VSOP Orbiting Very Long Baseline Interferometry (OVLBI)
experiment. OVLBI allows high resolution imaging of very distant
bright sources. I describe the design and operation of this instru-
ment, which we installed at Green Bank Observatory, and with which we
performed OVLBI experiments on a baseline consisting of the GB140-foot
telescope and the VSOP satellite. We have not yet detected fringes,
although we have successfully observed Galactic maser emission in W49
with the 140-foot by using the NRTC as an autocorrelator.

Low surface brightness radio structure has been discovered in the
field of the gravitational lens 0957+561. The emission is diffuse and
so faint as to be near the limiting sensitivity of the Very Large
Array, the instrument used to perform the observations. Nevertheless,
by coadding many data sets and carefully calibrating we map the
features and identify several which may be lensed. An arc 5 arcseconds
to the east of G may be a stretched image of emission in the
background quasar's environment. 1.4 arcseconds southwest of G we
detect a source that we interpret as an image of emission from the
quasar's western lobe, which could provide a constraint on the slope
of the gravitational potential in the central region of the lens. We
explore the consequences of these new constraints with simple lens
models of the system.

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