Jae's Spring 2008 page

• Remind yourself 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?

• Remind yourself 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
  
  You answered these questions in a homework for Astro 233; remind yourself:
  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/NAME/spr08 (substitute whatever login name you ask Tom to give you; but I need to set up the directory for you, so write me when you have your account. 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.

• Least squares fitting exercise:     Kim is also working on this; you may want to discuss it with her.
  1. Read about least squares in the on-line guide to Numerical Recipes. The section on least-squares is Chapter 15.1; there is a copy of the book in the Camuy Cave. Prof. Saul Teukolsky is one of the authors of this book, so computers at Cornell can access the code.
  2. Look at the Astronomy IDL routine FITEXY. Be sure that you understand what the routine does.
  3. Download Table 2 of Springob et al. 2007 from the Cornell EGG Digital Archive.
  4. Use FITEXY to fit the relation between x = column (6) [log of corrected line width] versus y = column (10) [corrected absolute magnitude]
  5. Fit y = ax + b and x = cy + d; do you get the same result? Make some plots. Think about and discuss your results.

• Groups and clusters of galaxies in the ALFALFA volume
  Your project will be to investigate the group and cluster environment in the local universe, how we identify hierarchical structures in a redshift catalog, and how ALFALFA can explore the group/cluster environment.
  1. Look at the paper by Kent and Gunn, 1982, AJ 87, 945. This paper uses redshifts to study the dynamics of the Coma Cluster. Notice Figure 1: that's a very handy way of trying to identify what objects are members of the cluster and which ones lie along the same line of sight but are not members. You do not need to understand all the details of this paper, i.e. its modeling of the cluster potential. Save that for another day.
  2. Learn about the Abell catalog, perhaps most famous catalog of "rich" clusters of galaxies. See the original Abell 1958, ApJS 3, 211.
  3. Read about the basic percolation algorithm for identifying groups in the paper by Huchra & Geller 1982, ApJ 257, 42.
  4. Think about some questions, or at least, how would you go about answering them?
     • What's the difference between a cluster and a group?
     • How many Abell clusters are in the ALFALFA volume?
     • Why isn't the Virgo cluster an Abell cluster?
     • What is the RASSCALS survey?
     • What is the velocity dispersion of Abell 999?
     • What do X-ray observations of clusters teach us?
     • What other questions can you ask?

• Assignment for next few weeks (Progress report due Mar 24; 2nd report due Apr 14):
  1. Prepare a short presentation for the class on groups of galaxies and percolation algorithms, to be given on Monday April 21st.
  2. Discuss with Martha how you might try to develop a percolation algorithm which you can run on an input catalog like the AGC; then try it. Here is a file with a sample to work with.

Summer Fun!

• Learn to use the ALFALFA catalogs.
  • Here is a small ALFALFA catalog. Practice with this one first.
  • Here is a bigger spring sky Mar08 ALFALFA catalog.
    You need to understand what is in the catalog, what the codes mean, etc.
  • Read the first ALFALFA catalog paper Giovanelli et al. 2007 AJ 133, 2559 which describes the survey and how the catalogs are constructed. Take notes. Ask questions!
  • Since it isn't documented elsewhere, make up a web page which explains everything you (or anyone) needs to know about what's in an ALFALFA catalog.
• Read the IDL version of the AGC. You can find the IDL structure (save file) of the AGC at: "/home/dorado3/galaxy/idl_alfa/agctotal.sav".
  • Find the AGC galaxies that occupy the same (3-D) volume as the master0803 ALFALFA catalog (above).
    07h30m to 16h30m and +04deg to +16deg and cz < 18000 km/s.
• Learn to use Ann's IDL program to calculate the distance to a galaxy starting from its position and heliocentric velocity.
  • See the file:///home/dorado3/galaxy/leggweb/distcalib.html for info.
  • Why do we have to correct the observed heliocentric velocity in order to calculate distance? Write up a section on this issue on your web page.
• Percolation program: keep working on that.