Data analysis

• Image reduction:Take bias, dark, and flat fields.

  
  

• Next, I stare at the processed images looking for faint galaxies. (example)

  
  

• The surface brightness profile of the galaxy is then found, using the IRAF and GASP software packages:

  
  

  • GASP fits ellipses to the galaxy, getting a (sky subtracted) intensity at each radius.

  • The surface brightness is found by:

  • The surface brightness profile for each galaxy is then plotted against the major axis. A best fit line is given to the linear part of the profile:

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The Data So Far

• Three sets of data have been taken so far by Cornell & Chappell on the McDonald 30" telescope using a 2048x2048 CCD camera.

  
  

• Johnson UBVI Filters:
  U 3650Å, B 4400Å, V 5500Å, I 8000Å

  
  

• The data covers the following sky areas:

  

  
  
  

• Some results:

  • Of the 270 galaxies found, 93 (+/- 6) have a central surface brightness fainter than 22.0 B.

  • The surface brightness profiles vary considerably.

  • The mean central surface brightness of these galaxies is 23.05 +/- 0.08 B. (See graph.)

  • The average colors of the 93 galaxies are (see graph.)

    <u-b>=0.316+/-0.04

    <b-v>=0.568+/-0.04

    <v-i>=0.893+/-0.06, <b-i>=1.87+/-0.20

  • The only apparent correlation in the data is between B magnitude and surface brightness (see graphs).

Things to come

• King profiles

• Red shifts - accurate h, distances, density

• MORE DATA

references