Kim's Spring 2008 page

• What is your project? Why do we want to study the highest HI mass galaxies detected by ALFALFA?
• How do we correct the observed magnitudes of galaxies for:
  1. galactic extinction (our location within the Milky Way)?
  2. internal extinction (within the galaxy itself)?
  3. redshift (the "K-correction")?
  4. differences in instrumental/filter response and/or bolometric corrections?
• What magnitude system is used for SDSS?
  See this link
• What is the DIRBE sky map and why/how is it used to estimate galactic extinction?
• What does the distribution of all HI masses in the catalog you are working with look like? Is it Gaussian?

• 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:     Jae Hwan and Lamarr 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.

• Assignment for next few weeks (Progress report due Mar 24; 2nd report due Apr 14):
  1. Prepare a short presentation for the class on high mass galaxies in ALFALFA, to be given on Monday April 14th.
  2. Checkout a new list, generated by Martha from the March 2008 master ALFALFA catalog
  3. Gather together the data needed to calculate the corrected stellar masses.
  4. Find out which of your high mass objects have SDSS spectra. Brian and Martha can help you use Brian's new routines to fine SDSS matches to a catalog.

Some useful links to help Kim answer her questions

• Read about the SDSS photometric system. The older Thuan-Gunn (1976) system used at Palomar was called "uvgriz"; the SDSS is close to those but not quite, so it is: "u'g'r'i'z'". See also Fukugita et al, 1996.
• The K-correction is described on Mike Blanton's website; put a link to that on your website. Check out Hogg et al, 2002. (I think you already did; it would be a good idea to put the links on your web page, besides at the bottom of your page.)