Arecibo Observatory

Preparation for UAT 2015 Workshop Preparation Planning Telecon


At the January 2015 workshop, we will target faint galaxies that are suspected to be gas-rich according to their optical properties, but that were not detected by ALFALFA because of their low mass. Detections will tell us their gas mass and their distance, allowing us to understand better the number, distribution, and dark matter content of low mass galaxies. This telecon will discuss background on ALFALFA and the Sloan Digital Sky Survey.

Background Reading


  1. ALFALFA and SDSS are known as "blind surveys". What does this mean? Why are blind surveys useful?
  2. Describe briefly the Sloan Digital Sky Survey (SDSS)? What kinds of observations are available through the SDSS?
  3. Describe briefly the ALFALFA survey? What measurements can we make of galaxies detected by ALFALFA?
  4. Should we expect to detect all galaxies in both SDSS and ALFALFA? Why or why not? What kinds of galaxies would each survey be most sensitive to?
  5. Let's say we find a galaxy in the Sloan Digital Sky Survey that seems to be blue and star-forming, but it wasn't detected by ALFALFA. Should we assume the galaxy has no HI gas? What is a more likely explanation?
  6. What is the "missing satellite" problem? What is meant by "satellite" in this context and why do we think they are "missing"? (The Science of ALFALFA page will be helpful in answering these questions.)
  7. What is a dark galaxy? Has ALFALFA found many dark galaxies so far? Check out the α40 catalog paper especially Section 4, which describes matching between SDSS and ALFALFA. Section 4.3 gives results. Do you think existing dark galaxy detections can solve the missing satellite problem?

Answers will be discussed in the First Observing Proposal Planning Telecon

Last modified: Thu Nov 13 08:05:36 EST 2014