UAT08.01 Scavenger Hunt #2: IDL AGC Utilities for ALFALFA
The purpose of this scavenger hunt is to introduce you to the ALFALFA
IDL utilities which allow you to anticipate
or check what galaxies ALFA swept across during an observing period.
To participate in the scavenger hunt,
you need to keep track of how you found your answers; Your method is
as important as the answers!
- 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.
"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.
- "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
- What's a "aitoff projection"? Why do we use it?
- What do you think causes the strong inhomogeneity in the source
population distribution seen in the galactic coordinate aitoff plot?
- 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>!
Now you are ready to try out Hunt #3!
This page created by and for the members of the
ALFALFA Survey Undergraduate team
Last modified: Tue Jan 8 15:23:17 EST 2008