Session 3 -- File based profiling by intensity analysis

 

Session 2 showed how one or more galaxies on an image might be processed interactively to yield their profiles. However, there are times when you want to profile virtually every object in an image. This can be done using ELLPRO or ELLFOU in essentially the same manner. The only difference is that you supply the image co-ordinates of the galaxies you want profiled in a text file. Such a file may be easily created using the LOGFILE option of KAPPA's CURSOR or by taking information from a file generated by object identification software such as PISA.

The file used in the example below, contains the following:

426.8958 155.2692
278.7055 299.9713
206.613 350.2151

The columns represent the x and y co-ordinates respectively. A third column might also have been included, giving a value for the background to be used for each of the galaxies. In the absence of a third column, the image's global value is employed. Local background values for different points may be easily determined using the ESP LOBACK application.

The co-ordinates given in this file should be in the Current co-ordinate system of the image (which can be selected by WCSFRAME as described in the previous section), so that for instance if the image had the SKY frame as Current, a suitable file might read something like:

 0:07:21.4   30:33:04
 0:07:42.6   30:32:10
 0:07:22.9   30:27:20

An example of the sort of input required is shown below.

% ellpro
 
ESP ELLPRO running.
MODE - Use the application interactively? /TRUE/ > f
INFILE - Text file containing co-ordinates /@coords.dat/ > f5coords.dat
IN - Image NDF filename /@ic3374c/ > f5flat
FRZORI - Is the galaxy origin to be frozen? /FALSE/ > 
BACK - Background value /760/ > 22712
SIGMA - Standard deviation of the background /12/ > 57
PSIZE - Size of the pixels (in arcsec) /1/ > 1
RLIM - Maximum ellipse radius (in pixels) /10/ > 40
ZEROP - Surface brightness zerop point (in magnitudes per arcsec) /27.5/ > 
AUTOL - Automatically search for better origin? /TRUE/ > 
AUTOLT - Use a centroid? /TRUE/ > f
Default background used for object at  426.9,  155.3 
Default background used for object at  278.7,  300.0 
Default background used for object at  206.6,  350.2 
ARDFIL - Masking ARD file /@ardfile.dat/ > !
WARNING! - ARD file not used.
OUT - Text file for profile output /@testprof.dat/ > f5results.dat
 
Working on PIXEL co-ordinates: 426.9  155.3
  19 ellipses determined.
Working on PIXEL co-ordinates: 278.7  300.0
  30 ellipses determined.
Working on PIXEL co-ordinates: 206.6  350.2
  12 ellipses determined.

Note that since the image in this example does not have a SKY frame in its World Coordinate System component, you have to enter the PSIZE parameter by hand.

In the example given, the co-ordinates file coords.dat identified the locations of 3 galaxies, but it could just as easily have contained information on many more. The current upper limit imposed by ESP is 10000.