1. [50 pts] For this problem set, you will work with a sample of surface brightness profiles of dwarf galaxies. There is much discussion in the literature about possible morphological evolution between gas-rich and gas-poor dwarf galaxies after a starburst episode. For a passive evolutionary scenario, the stellar distributions of both types of dwarf galaxies should be similar. In this homework, you will fit Sersic profiles to the observed surface brightness profiles of dE and dI galaxies to investigate passive evolution models.
The surface brightness profiles are located on the common file system server on the computers in Rm 311. You can access the common file server by logging in remotely to any of the machines gamma2 to gamma10. Once you are logged in, you can access the data by going to /home/vanzee/A575. There are 2 directories, dE and dI. You may wish to copy the files onto your own computer, but it is not necessary to do so.
Each directory contains the surface brightness profiles for several galaxies. In addition, the file galaxies.list contains potentially useful information (distance and extinction) for each galaxy.
File format: The files *.dat contain selected values from the surface brightness fit (obtained with the IRAF task ELLIPSE) for each galaxy. The top of the file has some header information, including column descriptions. sma2 is the semi-major axis, mag is the magnitude within the aperture, and surfmag is the surface brightness within the annulus. The dE data are for R-band images, with B-R colors for surfcol and col. The dI data are for V-band images, with B-V colors for surfcol and col. ELLIP and PA are the ellipticity and position angle for the ellipse.
(a) Using supermongo, plot the surface brightness profiles of the dE and dI galaxies. In your plots, clearly label the axes and specify which galaxy is which. You may wish to plot multiple galaxies per page to save paper.
(b) Write a program that fits a Sersic function to the observed
profiles:
I=I(0)exp[-(R/Ro)n]
You will need to use a non-linear minimization routine to solve
for the 3 parameters (I(0), Ro, and n). The Numerical
Recipes routine MRQMIN is one option. For those of you who program
in fortran, you can link directly to the numerical recipes library in my
directory (-L/home/vanzee/numrec/lib -lrecipes_f). For those
who program in C, you can find the code on the numerical
recipes books-on-line page (http://www.library.cornell.edu/nr/nr_index.cgi).
Alternatively, you may wish to use routines in the gnu scientific
library (gsl).
Tabulate your results and overplot the resulting fits to the surface brightness profiles shown in part (a).
(c) Compare the results of your fits for the dE and dI galaxy samples (i.e., create plots of the parameters I(0), Ro, and n). Based on your data analysis, comment on whether a passive morphological evolution model is possible for dwarf galaxies.