Hong's Spring 2008 page

• Learn about the ALFALFA survey and, especially, take a look at the Using ALFALFA for science page. What does ALFALFA detect? How can we use ALFALFA to learn about galaxies?

• Read about the Sloan Digital Sky Survey in order to answer these questions. Some useful links are given here:
  Main SDSS site         DR6 site        Imaging camera parameters and description
  
  a. What is the operational status of the SDSS?
  b. What are the central wavelengths of the filters used to produce SDSS images?
  c. Why is it useful to obtain images in 5 filters simultaneously?
  d. Over what portion of the galaxy is the spectrum obtained? Why might that be important?

• Make a web page for yourself to keep track of what you are doing; you should put it in the directory called /home/hatillo/hongyuxiao2000/spr08. See my hints on how to get started.

• Numerical integration of an HI profile
  1. Use our links to find the ALFALFA data entry for AGC/UGC 7192. Put the link on your webpage.
  2. On your webpage, record for yourself the ALFALFA catalog information for this object. Do you understand what the parameters mean? Add notes for your own reference, as needed. If possible, enter the data as a table on your webpage; if you don't know how to do it, ask for a hint.
  3. Make a link on your web page to the journal article containing the ALFALFA publication of this spectrum.
  4. Download the spectrum (ASCII file format) to your disk area on hatillo.
  5. Write an IDL routine to calculate the integral under the profile. If you run into "issues", ask! This will probably take you some time as you need to know how to read in a file, among other things.

• The Arecibo General Catalog (AGC) is our private database containing basic data on several hundred thousand galaxies. It is not intended to be used by or distributed to people outside the ALFALFA collaboration.
  1. 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?

• The EGGGEN utilities:     Hong, you should learn to use these utilities and then we'll have you demonstate them to the rest of the group.
  1. Learn how to start up IDL accessing the Arecibo and ALFALFA utilities. For this, you'll have to ask one of the local experts.
  2. "plotalfa"
     "plotalfa" allows you to explore how ALFA scans accross a region of the sky using the ALFALFA observing mode. 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.
     • Investigate the 12h41m30s,+26d02'12" field. 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?
     • 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.

  3. "agcbrowse"
     "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
  4. What's a "aitoff projection"? Why do we use it?
  5. What do you think causes the strong inhomogeneity in the source population distribution seen in the galactic coordinate aitoff plot?
  6. 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!

• Investigating the IDL code for "agcbrowse":     Try to understand what the IDL routine "agcbrowse.pro" actually does.
  
  1. Click here to download your own version of "agcbrowse"; save it to a file called "agcbtest.pro".
  2. Study the code and try to understand what each segment does.
  3. You can run it by compiling it within IDL
     .compile agcbtest.pro
  4. See if you can write a separate routine which reads the AGC and plots variables from it (x versus y).

• Reading ALFALFA catalogs:     ALFALFA produces catalogs containing a source name, the AGC number (where there is one), the HI centroid and the position of the optical counterpart, and then various parameters measured from the HI line. Write yourself a short IDL routine to read this test catalog (this is the one Kim is also using), and try to calculate the HI mass from the parameter SintP (which is the HI line flux density in units of Jy-km/s). The column labeled "v50" is the heliocentric recessional velocity in km/s. If you have questions, you might ask Kim, since she is also using this file.