UAT08.01 Scavenger Hunt #1: Utilities for ALFALFA

• Be sure you have answered all the questions in Hunt #0 before you tackle this set.

• The Arecibo General Catalog. Members of the ALFALFA team have access to the private database dubbed the "AGC" which is compiled and maintained by Martha and Riccardo at Cornell (for more years than we will admit!).
  1. If you misuse it, you may become the proud wearer of a pair of cement shoes. What are the conditions of use?
     Look here for the answer and follow the link to answer the next questions.
  2. What is the "UGC"?
  3. When is the AGC entry number equal to the UGC entry number?
  4. What is the "position angle"?
  5. What is the "TELCODE" for Arecibo+ALFA?
  6. Some galaxies have two velocity measurements: "VOPT" and "V21". In that case, what should you adopt as the recessional velocity for the galaxy?
  7. Sometimes, "V21" is entered but does not indicate the redshift of the galaxy. Why not? Find us an example.
  8. Sometimes "VOPT" is actually a 21 cm velocity. Some of these are easy to identify. How? Find us an example.

• Try out the ALFALFA stand-alone utilities. These are executable FORTRAN codes that are aliased in the "alfalfa" account at Arecibo on the LINUX (not SOLARIS!) side. (Note: If you don't have these installed locally on your own machine, that's ok. Skip this part and go to Hunt #2.)
  Notice that coordinates are usually entered by us (as they are entered in the AGC), i.e., without decimal places or spaces in format hhmmsss+ddmmss. The seconds of RA is entered in 0.1sec, as an integer.
  1. "plotd"
     Let's take a look at the part of the sky that ALFA will cross during our planned observations for the run 08.01.14. "plotd" plots the ALFA beam tracks and the distribution of galaxies in a 3x3deg region of the sky starting at a given (RA,Dec). The galaxies are color coded by recessional velocity, larger ones with diameter and position angle information are shown as properly oriented polygons (but the scaling is for illustrative purposes only!). You can interactively retrieve a summary of the basic AGC entry information by clicking on each galaxy in the display. Run "plotd" on the drift beginning at R.A. = 12h36m, and Decl. = +26d02'12".
     • What is the largest galaxy in the frame?
     • What ALFA beam will sweep across the center of that gelaxy?
     • What is the position angle of that galaxy?
     • Has the galaxy been detected in HI before?

  2. "skyd"
     "skyd" generates an HTML file containing a set of links to SDSS, DSS1 (via Skyview), DSS2 (red and blue) and NED for a given position (entered in "AGC style": hhmmsss+ddmmss). NED entries with 10 arcmin are returned; images of 2 sizes can be examined for the DSS sets. The HTML file is called "skylinks.html" which you then need to load into your browser. It is created in the local directory where you are working so you need to keep track of where you are working; be sure not to write over someone else's file! Run "skyd" on the position RA = 12h41m30.0s, Dec=+26d02'12" and experiment with the links. If you do not have much familiarity with NED, SDSS and DSS1/2, you should certainly learn more about them by visiting their own websites.
     • What do you find there?
     • At what zooming scale can you see the large galaxy discussed in the previous exercise.
     • What do you notice about the availability of SDSS spectroscopy in this region (at least as of Jan 2008)? How did you figure this out?

  3. "plot30" (superceded by idl_alfa routine "plotalfa", see below, but useful if you don't want to open IDL)
     Now let's take a look at the small group of galaxies you noted in the observing proposal. "plot30" plots the location of the ALFA beams at the instant Beam 0 sweeps across the input position. The beam tracks are shown, and you can interactively retrieve a summary of the basic AGC entry information by clicking on each galaxy in the display. Run "plot30" on the position RA = 12h41m30.0s, Dec=+26d02'12" (just as above).
     • We might expect the HI signal from UGC7852=NGC4615 to be detected in which beams?
     • Which beam will detect the galaxy FIRST (in the LST time of our observations)?
     • Will we be able to distinguish the signals from the three galaxies? What is the problem? Discuss the issues involved.
     • Try another position: RA = 11h22m00.0s and same center declination as the drift. Discuss what you find.

  4. "a2010fv"
     The ALFALFA observing setup uses the WAPP spectrometers which deliver specta which cover 100 MHz total, centered on 1385 MHz; each spectrum has 4096 "channels" (or "pixels", "array elements", however you want to think of them). "a2010fv" calculates the frequency and recessional velocity (sans heliocentric correction -- it's not exact! -- assume simply that v = c*z) corresponding to each channel in an ALFALFA spectrum.
     • What frequency/velocity correspond to channel 2048?
     • What are the units of frequency and velocity?
     • Does velocity increase or decrease with increasing channel number? What about frequency?
     • What channel corresponds to a redshift of 0.03?
     • Write down the formula used to convert from frequency to velocity. Hint: assume the simple expression v = c*z; but use the "optical convention" for the doppler shift.