The Survey: The Arecibo Legacy Fast ALFA survey is a blind extragalactic survey in neutral hydrogen (often called HI by astronomers). The goal is to find about 25,000 galaxies. The blind part of the survey refers to the fact that observations are not targeted. Instead of pointing at specific targets that have been preselected, the telescope is pointed at one location for the night and the sky is allowed to drift pass (this is referred to as a drift-scan). The idea is that this avoids bias in having to select objects a priori – we’d like to find galaxies that have not been previously detected. The project website can be found here and a general overview for the non-expert is located here.
Arecibo: The Arecibo radio telescope is the world’s largest single dish telescope. Located in Puerto Rico, it has a diameter of 305 m (1000 ft). The size of this telescope offers two advantages to observer: better resolution and better sensitivity than other single dish telescopes.
ALFA: The ALFALFA survey utilizes ALFA, the Arecibo L-band Feed Array, a new seven “pixel” detector available at Arecibo. While seven pixels is small compared to optical wavelengths (and your common digital camera), it is a vast improvement to previous generations of instruments that were a single pixel. It allows the sky to be mapped seven times faster than possible before, making a survey such as ALFALFA feasible.
The Welcome post describes the goal of this blog and is a spot for asking questions about ALFALFA.