#AUTHOR: CALIFA collaboration
#SOURCE: SDSS DR7 images and own analysis
#DATE: 2014-09-09
#VERSION: 1.0
#COLAPRV: none
#PUBAPRV: none

This table provides the results of a reanalysis of the SDSS DR7 images. 

SExtractor was used to detect stars and other sources in the image to create a pixel mask 
for all the sources except the CALIFA galaxy. The mask was visually checked and manually 
corrected, if necessary.

Simple interpolation would not by definition have been applicable, so we chose a procedure 
known as inpainting in the computer vision community, i.e. masked pixels were iteratively 
replaced with a Gaussian inverse-distance weighted average of the neighbouring real pixels, 
starting with the pixels with the largest number of nearest neighbours. In order to apply 
the masks (originally created for the r band images) to the other 4 SDSS bands, we measured 
the shift between the different images and their r band counterparts using their WCS (FITS 
World Coordinate System) ra and dec coordinates, then shifted the masks and cropped the images 
accordingly.
                                   
The position angle and ellipticity of the galaxies were measured based on the light moments 
of the masked galaxy image (compare the SExtractor manual for definitions of the light moments). 

The growth curve analysis was performed in both elliptical and circular (r-band only) incrementally 
increased annuli.


If the flux profile was fitted in sufficiently wide rings using simple
linear regression, the best fit line should become horizontal at some radius,
which might then be considered the edge of the galaxy. This would assume that flux
falls off asymptotically until it is indistinguishable from the sky fluctuations.
In practice this is not the case, given that incomplete masks, light from
other objects and sky gradients make the best fit slope switch from negative
to slightly positive at some point. We therefore fit 150 px sections of the flux profile
using simple linear regression, making the neighbouring fit sections overlap by 100 
pixels. When the flux profile slope becomes non-negative, we take the mean of the
current ring as the sky value, and the ellipse with major axis value at the
middle of the ring as the galaxy's edge.

After measuring the galaxy's extent and sky value, the flux within the galaxy was summed up, 
sky was subtracted and u, g, r, i, z magnitudes were calculated.

The counts were converted to magnitudes, as described here:
http://www.sdss.org/dr7/algorithms/fluxcal.html#counts2mag
87 galaxies had no zeropoint/extinction/airmass given in corresponding file
headers, in such a case the mean values of these parameters in a given band was used.


The magnitudes were converted to AB magnitude system by applying zeropoint correction as 
described in http://www.sdss3.org/dr8/algorithms/fluxcal.php#SDSStoAB. The correction is 
as follows: u_{AB} = u_{SDSS} - 0.04 mag
The unconfirmed z band correction, z_{AB) = z_{SDSS} + 0.02 mag, was not applied

The half light radii (semi-major axes for the elliptical case) were obtained by taking the 
semi-major axis value of an ellipse such that half of the total flux lies inside or on it, 
and multiplying it by the SDSS pixel scale (0.396).

A set of quality flags were also introduced after a visual inspection, denoting
uncertain position angle values, incorrect center coordinates (a significant
offset), unreliable measurements. The last column in the table is the sum of
quality bit flags. The meaning of the individual flags are:

-- 1: Visually wrong PA
-- 2: Visually wrong center (large offset)
-- 4: Unreliable photometry: bad masking, distorted shapes due to inpainting, too close to 
      a frame border, weird shape of the growth curve.