Precisely how galaxies initially form and how they change throughout their lifetime are among the least understood problems in astrophysics. Many projects are centered on unraveling these mysteries. This project aims to provide the first robust census of gas-rich halos over a cosmologically significant volume and intends to provide important insight into how some massive galaxies maintain huge gas reservoirs without converting their gas into stars and how isolated low mass halos are able to retain some atomic hydrogen gas despite their fragile thermal state and shallow potential wells. This proposal is intended to conclude the already initiated survey, previously funded by NSF. The conclusion of the survey was understandably delayed primarily by telescope downtime but should conclude by the fall of 2012.
The survey is conducted at the Arecibo radio telescope and uses the Arecibo L-band Feed Array (ALFA), the Arecibo Legacy Fast ALFA (ALFALFA). The survey has already produced results far exceeding the previous survey in this field, and the survey results will help to characterize the mass function of such halos and allow direct comparison with theoretical simulations of Universe in the current Lambda-CDM paradigm. ALFALFA, an extragalactic HI 21 cm line survey, will identify HI-bearing objects found over 7000 square degrees of the high galactic latitude sky out to z < 0.06. The public ALFALFA database includes HI line spectra and catalogues of HI line positions, redshifts, velocity widths, and flux densities as well as coordinates and cross-identifications in other digital data sets of the most probable optical counterparts.
This project has educational broader impacts as well. Graduate students will be intimately involved in all phases of the project, helping to plan and execute the observing program, developing software for data processing and analysis, producing public data products and interfacing with the Virtual Observatory, as well as undertaking their own science projects. Educational materials that are developed as part of this project will be made available through the existing ALFALFA public web site.