The aim of the workshop was to anticipate the principal areas of scientific research that could best be explored with the upgraded telescope and to discuss the necessary tools. The Arecibo staff provided an overview of the upgraded system for L-band and related instrumentation, and received suggestions from their future customers. The format combined short talks on potential research topics with more extensive open discussions on areas of general interest such as redshift surveys, dwarf galaxies, and mapping with the upgraded telescope.
Daniel Altschuler welcomed the participants and reviewed the HI science proposed in the 1986 workshop that had stimulated the plans for the upgrade in the first place. Morton Roberts (NRAO) put the investigation of extragalactic HI in perspective by presenting many puzzles concerning the HI content of normal galaxies that have yet to be solved, such as the morphological type dependence and the time scales for evolution, the extent of the gas as compared to the stars, extremely gas-rich systems, environmental and tidal effects, and simply understanding the single-dish 21-cm spectral line profile.
Several forthcoming redshift surveys that will benefit from the upgrade were discussed. The goals of these surveys are 1) to improve our understanding of the distribution of matter in space, and 2) to find previously undetected or uncataloged objects in order to determine the HI luminosity function and to more fully describe the entire range of galactic properties. Because of its sensitivity and extended frequency coverage, the Arecibo telescope is needed to follow up detections and to stretch the redshift limits using long integrations with its narrow pencil beam at 21 cm, which would sample a potentially large volume of space. Although the large-scale distribution of galaxies may best be studied by dedicated redshift surveys, such as the Sloan or Las Campañas surveys, the growth of structure may be better approached at a smaller scale, such as can be provided by the Arecibo telescope.
Several talks pointed out other research areas that could be addressed with the upgraded instrument. By observing galactic clusters with bandwidths of 12,000 km/s and the sensitivity of the Arecibo telescope, peculiar motions can be used to probe bulk flows and constrain the biasing parameter. Comparing clusters at increasing redshift can test for evolution in the Tully-Fisher relation. Sensitive observations of the Zone of Avoidance can delineate the galactic structures behind it. Also, highly redshifted HI absorption studies at 300-350 MHz can provide information on the kinematics of protodiscs, while high redshift emission can be used study the Butcher-Oemler clusters to an HI mass of 1013 solar masses at z = 4.
The upgraded telescope can also tackle many scientific questions related to Galactic HI. Mapping specific targets, such as high-velocity, intermediate-velocity, and high-latitude clouds, and the 100-mm emitting cirrus, can help to settle questions on the dynamic processes of the interstellar medium. Arecibo's small beam can be used to find holes in the Galactic gas through which soft x rays can be viewed. Neutral hydrogen mapping can also provide information on molecular clouds that show up as HI in absorption. The amount of absorption will distinguish between arm and interarm regions.
Because of its sensitivity and beam width, the Arecibo telescope can map to very low column densities, and therefore is unique in its ability to explore how far out HI emission goes in a galaxy and to map large, intrinsically low column density objects. It can also be used to fill in the missing short spacings for VLA images. Both Galactic and extragalactic observers were very excited about the potentials of on-the-fly mapping with the upgraded telescope and recommend that it be implemented as soon as possible.
Participants also urged that the Observatory acquire full VLBI capability. Many important VLBI experiments can be accomplished only with the participation of the Arecibo telescope. The post-upgrade continuous frequency coverage overlaps with six VLBA bands, two VSOP bands, and three RadioAstron bands, and also provides bands not covered by the VLBA when used in collaboration with other frequency-agile telescopes. The inclusion of Arecibo with its high sensitivity improves the signal-to-noise ratio by factors of up to 24 depending on the frequency of observation.
The participants left Puerto Rico excited about observing with the new upgraded telescope. We hope to be able to accept their observing proposals soon.
Copyright 1996, Cornell University
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