This README file describes the AEGIS F814W<25.2 training sample, which is a
randomly ordered sample of galaxies in the AEGIS field in F606W(V) and F814W(I) bands with AB magnitude in I band <25.2.
The galaxies were detected in the summed V+I image 
and the entries in the V and I catalog files correspond to the same galaxies.

NOTE: The columns in the catalog are those expected by galsim.RealGalaxyCatalog.
The catalog can also be used with galsim.COSMOSCatalog() without parametric fits. 
Drawing parametric galaxy in galsim.COSMOSCatalog() requires another file 
with information on parametric fits performed on galaxy images.

(1) The catalogs themselves are in AEGIS_galaxy_catalog_[VI]_25.2.fits (where
[VI] indicates either V or I). These files can be used to initialize a
galsim.RealGalaxyCatalog or galsim.COSMOSCatalog instance, and contain a FITS
tables that could also be  read in directly using, e.g., python or IDL.  The
fields that are included for each galaxy are:

IDENT: AEGIS object identifier. This value is internally derived. Therefore
do not rely on this IDENT for cross-matching between other AEGIS catalogs.
IDENT in V and I catalogs correspond to the same galaxies. 

RA, DEC: Right ascension and declination (J2000, degrees).  While this is not
needed for image simulation, it is necessary for proper cross-matching with
other catalogs.

MAG: magnitude (MAG_AUTO calculated from sextractor).

BAND: Passband for the observed image (F814W/F606W).

WEIGHT: A weight factor to use to account for size dependent selection effects.

GAL_FILENAME: Name of the file containing the galaxy image.  This is just a
filename, not including a full path.

PSF_FILENAME: Name of the file containing the PSF image for this galaxy.
This is just a filename, not including a full path.

GAL_HDU: HDU containing the image of this galaxy in the file called GAL_FILENAME.

PSF_HDU: HDU containing the image of the PSF for this galaxy in the file called PSF_FILENAME.

PIXEL_SCALE: pixel scale for the galaxy and PSF images in arcsec (0.03 for all bands).

NOISE_MEAN: mean value of the pixels in the image that do not contain the galaxy.

NOISE_VARIANCE: variance of the pixel values for pixels in the image that do not contain the galaxy.


(2) The files containing galaxy and PSF images are
AEGIS_galaxy_images_[VI]_25.2_n?.fits and AEGIS_galaxy_PSF_images_[VI]_25.2_n?.fits. The number that goes in place of the "?" ranges from 0 to 29.

(3) Files (AEGIS_galaxy_catalog_[VI]_25.2_selection.fits) with some selection
flags that the GalSim COSMOSCatalog class may use to impose selection criteria
on the quality of the postage stamps and/or fits.

IDENT: AEGIS identifier.

dmag: not used

sn_ellip_gauss: SNR of the galaxy measured with an elliptical gaussian filter.

min_mask_dist_pixels: Distance from the center of postage stamp to the nearest masked pixel.

average_mask_adjacent_pixel_count: Average pixel value of the 3*3 pixel region around the nearest masked pixel, before masking.

peak_image_pixel_count: Highest pixel value of central object in postage stamp.

(5) Files acs_[VI]_unrot_sci_20_cf.fits containing information that GalSim
needs to understand the noise fields in the postage stamps.
