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README file for the COSMOS/ACS morphological catalog from
the Columbia University group version 1.0
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Objects in this catalog were selected from the 2005 release
of the ground-based photometry catalog, with the criterion
that their I-band (auto) magnitude had to be <= 23. The IDs,
ra and dec provided in this catalog correspond to those of
that 2005 release. 

The catalog was cleared from stars and point sources as well
as from all sources for which the morphology code did not
run to completion.  Objects that could have been rejected
in that way include:  objects close to the edge of the
image, objects in dense tight groups and objects situated
in the proximity of a bright source. 

**************** Notes on asymmetry ***********************

Two values of asymmetry are provided, mainly for historical
reasons. The one assigned to the A-parameter is calculated
after recentering at a sub-pixel level and rebinning of the
object, whereas the one called "A_old" centers on discrete
pixels. Usually, A is more accurate than A_old, but in some
cases (mainly for large objects), A could be a slight under-
estimate of the actual asymmetry due to the mild blurring
that occurs in the rebinning process.

The asymmetry due to the background is calculated according
to the following formula:

A_bkg = (A_0 - A'_0) / (1 - 1/sqrt(5))

              and

A_0 is the absolute value sum of all residuals of the
original-rotated images (within the segmentation map)
divided by the total flux, and

A'_0 is the same thing except with each pixel in the
original image being replaced by the average of itself and
its four direct neighbours.

For a derivation of this formula see Zamojski et al. (2007).

***************** Notes on clumpiness *********************

The clumpiness of the background is calculated from four
regions outside the object, one in each quadrant. In the
output table, these are sorted from lowest to highest, and
are label "S_bkg_1" through "S_bkg_4". All clumpiness values
are "raw", meaning they indicate simply a residual sum.
In order to calculate the actual clumpiness one needs to
pick a value for the clumpiness of the background and use
the following formula:

   S = 10 * (S_raw - S_bkg) / Flux

Lowest or second lowest are good choices, since they have
less chances of being contaminated by neighbouring objects.
For the value of the S-parameter quoted in this catalog, we
used the highest of S_bkg_1 and the theoritically expected
value for a region of pure background:

 (N_seg - N_ker) * SIG_bkg * SQRT((N_ker+1)/(2*!PI*N_ker))

where N_ker is the number of pixels in the convolution filter.
In producing this catalog, we used a tophat filter.

***************** References ******************************

Further information can be found in the following paper:

Zamojski et al. 2007, ApJS, 172, 468

Also, I can be contacted at either of the following addresses

michel@astro.columbia.edu
zamojski@ipac.caltech.edu

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Written by Michel Zamojski, July 2008