Lamarr's Spring 2008 page

• What is your project?
• What observables do you need (i.e. what quantities need to be available) for your project?
• What observables does ALFALFA produce?
• 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/lamarrp/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!

• Before you delve into SDSS and ALFALFA, you can check out some of our recent work using the Tully-Fisher relation using I-band magnitudes and both 21-cm HI line and optical rotation curve data which is presented in Springob et al. 2007. The datasets are available through the Cornell Digital Archive and includes a set of cluster galaxies ("template sample") and others ("non-template sample"). Check it out. Perhaps you can begin your explorations of the methodology using those data?

• Least squares fitting exercise:     Kim and Jae Hwan will also be working on this exercise.
  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.

• The Hercules Supercluster
  1. Check out Barmby et al 1998
  2. Learn to read the AGC. You can experiment with and expand on this IDL program.

• Assignment for next few weeks (Progress report due Mar 24; 2nd report due Apr 14):
  1. Prepare a short presentation for the class on the Tully-Fisher relation and rotation curves to be given on April 14th.
  2. Devise a plan for how to move forward; what data do you need? Discuss with Martha.

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, and for your paper
• Write a program to calculate the HI masses of the galaxies in the ALFALFA catalog.
  See the "Using ALFALFA for Science" page on computing the HI mass.
• Nearest neighbors: continue working on your nearest neighbor routine.
  • Check the angular units you are using!
  • Check some by hand!
  • Once you have calculated the distances to your objects, you can convert from angular distance to linear distance.
  • Think about how you are going to correct for incompleteness at large distances. Do you understand the problem of incompleteness?
  • Start writing the background for your paper. Some sections you should be able to write already:
    • What is ALFALFA? What is a blind survey? How does ALFALFA differ from a survey like SDSS?
    • What is the HI 21 cm line?
    • Where is HI found in the universe? In a galaxy? (i.e. all parts, some parts?)
    • What are the parameters of the 21 cm line that we measure?
    • How can we calculate (a) HI mass, (b) distance, (c) dynamical mass....? Anything else?
    • Why would anyone want to determine the "local environment" of a galaxy?
    • What is a nearest neighbor analysis?
    • What is a luminosity function? an HI mass function? a selection function? (for the latter, pick Jae Hwan's brain...)
    
    To access Lamarr's progress page, type file:///home/hatillo/lamarrp/spr08/progress.html into your browser.
    
    
    

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    Last modified: Thurs Jul 17 14:12:10 EDT 2008 by martha