UAT08.01 Scavenger Hunt #2: IDL AGC Utilities for ALFALFA

• Be sure you have answered all the questions in Hunt #0 and Hunt #1 before you tackle this set.

• Try out the IDL_ALFA utilities included in the LOVEDATA package.
  To try these out, start up IDL for ALFALFA and then try out each command.
  1. "plotalfa"
     "plotalfa" is based on the stand-alone program "plot30" which you learned to use in Hunt #1. In IDL, it is developed as a widget which allows for more flexibility in specifying the region plotted. You can elect to see the galaxies and ALFA beams/tracks in a square box of variable size from 30 arcmin (0.5 degrees) to 10 degrees with allowed values of 0.5, 1.0, 2.0, 3.0 ...10.0 . The bigger the region, the more galaxies that are plotted.
     • Revisit the 12h41m30s,+26d02'12" field you investigated in . Here, enter the coordinates ("AGC style") and specify the box size to be 0.5 degrees; this is the same as "plot30".
     • How many galaxies do you find?
     • As you increase the box size, see how the number and distribution of galaxies change. What do you notice about the distribution of galaxies? How might this be explained? Hint: check your answers to the questions related to "skyd" in Hunt #1.
     • Set the box size to 5 degrees. How many objects do you find?
     • Recenter the box to 12h57m00s, +26d02'12". How many objects do you find? Why is the number so much larger?
     • Recenter the box to 10h30m00s, +26d02'12", and set the box size to 1 degree. Make note of the AGC numbers of a few of the galaxies; we'll use those numbers to test out "uagcbrowse" below. Include (a) the very edge-on galaxy to the east, and (b) the pair of galaxies just west of the beam 5 indicator.

  2. "agcbrowse" (or "uagcbrowse" but for smaller screens)
     Note: for full function, you must run "agcbrowse" on a machine connected to the outside world so that images can be retrieved; not all the machines at AO are.
     "agcbrowse" allows you to explore the entries in the "AGC" database for individual objects and/or to find all the AGC entries around a position. In this case, just to make things more "fun", the entry positions need to be in decimal hours and degrees hh.h, dd.d. It also retrieves the DSS2(blue) image at a position and displays its location of an aitoff map in galactic coordinates
  3. What's a "aitoff projection"? Why do we use it?
  4. What do you think causes the strong inhomogeneity in the source population distribution seen in the galactic coordinate aitoff plot?
  5. Enter the AGC number of the very edge-on galaxy to the east of the frame you explored with "plotalfa".
     • Has it been observed in HI before?
     • What telescope was used to observe it before?
     • Once you entered the AGC number, the coordinates in the "search by" widget will update. You can now query around that position; find the galaxies within 30 arcminutes. Experiment and learn to use this widget!