Exercises for ALFALFA January 2011 observing

Background Reading

• Review your understanding of the equatorial coordinate system (right ascension and declination). See first bullet in Things to Know for help.
• Review the Introduction to Arecibo Observing
• Review angular resolution, or beam size, of the telescope and how is it related to the diffraction limit at this link.
• Review the ALFALFA summary of 21-cm radiation, describing the 3 things the 21-cm spectrum tells you about a galaxy. Also review Hubble's Law.
• Check out the latest catalog including 40% of the ALFALFA survey area (Haynes et al. 2011). (alternate link) This paper contains a summary of sources detected by ALFALFA and is a good reference to answer questions 5-9 below.

Questions

1. What is the latitude of Arecibo Observatory?


2. Suppose we choose to observe a source with a declination of +12^o10'35" while it is on the meridian. We choose an azimuth angle of 360. What zenith angle would we use?


3. The ALFALFA survey is using the ALFA detector. But we plan to followup exciting ALFALFA detections using the L-Band Wide (LBW) detector. Why don't we use ALFA?


4. What is the frequency range covered by the L-Band Wide (LBW) detector? What wavelengths does this correspond to? Assuming that you were observing the 21-cm line, what range of velocities and redshifts does this correspond to? Compare to the coverage of ALFA.


5. What is the difference between Code 1, 2, and 9 targets in the ALFALFA cataloging scheme?


6. How are the optical counterparts of ALFALFA sources determined?


7. What might the Code 1 sources without optical counterparts be? Some might be real "dark galaxies", others are in known debris fields (what does "debris field" mean?). Check out this press release and the description of ALFALFA observations of Virgo HI21 for an example. See also John Hibbard's HI Rogues Gallery for other examples of tidal debris.


8. How would we know a dark galaxy if we saw one? What is the definition of a "dark galaxy"? Do "dark galaxies" exist? Should they?


9. What is meant by "completeness", "sensitivity" and "reliability"?

Complete your answers by Thursday, Dec 8