What is PyCA_?
PyCA (pronounced Pica, like itches in spanish) is a Python module that computes Concentraction and Asymmetry of galaxies using (preferentially) the by-products of SExtractor runs. Many studies have been devoted to study the morphological properties of HST (WFPC2 and ACS) galaxies using structural parameters and their link to visual morphologies. The Concentration and Asymmetry, (and their flavors) being particularly popular and well accepted. However, there are no public recipes or code available to compute them. In the tradition of open source and science code, such as IRAF, SExtractor and BPZ, PyCA is publicly available and open source to the comunity. It has been tested to run in Linux and Solaris. And should also run in Mac OSX provided you have all the required libraries installed.
Requirements_
Of course you will need Python, but any reputable machine should have it installed by default. You also need the following python libraries (in case you don't already have them)How to use_
PyCA runs in a list galaxies provided the by user in the form
of a multicolumn file with their identifications (IDs) in one of the
columns. These should correspond to IDs from an associated SExtractor
run with a SCIENCE flux image, a SEGMENTATION image
(i.e. dataset_SEGM.fits) and SEx detection catalog
(i.e. dataset.cat). Your values of A and
C will only be as good as your detection an deblending in your
science images are. There are 5 entries that your SExtractor catalog(s)
must have for PyCA to run. These are:
X_IMAGE, Y_IMAGE, A_IMAGE, B_IMAGE, THETA_IMAGE and
KRON_RADIUS.
For example:
%>PyCA selected_ids.dat --idcol 0 --flux=UDF.fits --segm=UDF_SEGM.fits --cat=UDF.cat --Petro
will compute A and C for list of galaxies contained in the file selected_ids.dat in the first column (idcol=0) using a Petrosian Radius, (--Petro) from a science image UDF.fits with their associate SExtractor segmentation image UDF_SEGM.fits and catalog UDF.cat. Aditionally, A and C can be meassured using the SExtractor's Kron Radius (--Kron) or the geometry defined by the segmentation image, if you don't specify a radius type. A detailed description of how A and C are calculated can be find in section 2.3 of Menanteau et al. (2005).
For a full list of command line options:%>PyCA --help
References_
PyCA is public software, you are welcome to use and encouraged to test it! If you decide to use PyCA in your science, please reference Menanteau et al. (2005), AJ. accepted (astro-ph/0509759).