09/09/2007
README file for COMBO-17 SED plots in the A901/902 field
contact:  Christian Wolf // cwolf [at] astro.ox.ac.uk


1.  INTRODUCTION
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STAGES (Space Telescope A901/902 Galaxy Evolution Survey) is a large
area (~0.5x0.5 degree) survey of the Abell 901(a,b)/902
multiple-cluster system at z=0.165.  The multiwavelength survey
incorporates 17-band optical photometry from the COMBO-17 survey,
including photometric redshifts and SED classifications.

This README documents the COMBO-17 SED plots available as part of the
STAGES public data release available at

http://www.nottingham.ac.uk/astronomy/stages/astro_data.html

For all details regarding the survey construction, data reduction, and
catalogue creation see:

M. Gray et al.
"STAGES:  The Space Telescope A901/902 Galaxy Evolution Survey"
MNRAS, 2008 (accepted)

To download the associated STAGES master catalogue (including
SExtractor and GALFIT parameters; COMBO-17 photometry, photometric
redshifts and stellar masses; and UV and 24 micron derived star
formation rates) or additional multiwavelength data, visit the STAGES
homepage:

http://www.nottingham.ac.uk/astronomy/stages/astro_data.html



2. NAMING CONVENTION:
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For each of the 63776 objects with COMBO-17 photometry there exists an
SED plot of the form:

stages_171207_nnnnn.ps.gz

where nnnnn is the COMBO-17 object id, given by column "COMBO_Nr" 
in the STAGES master catalogue available here:

http://www.nottingham.ac.uk/astronomy/stages/astro_data.html


  NB: for object Nr=33783 a new plot exists (stages_190808_33783.ps)
  with new template normalization to match the plot in Appendix A of
  Gray et al. 2008.



3.  SED PLOTS
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The SED plots show fluxes in every measured band in units of
photons per (m^2 sec nm) over wavelength. Data points are plotted
as error bars whose width corresponds to the width of the filter
and whose height corresponds to the 1-sigma flux error measured
from the scatter between the measurements of typically 10-20
individual frames. The solid blue line shows the best-fitting
template regardless of fit quality.

The various labels are:

top row:
filename of catalogue from which plot was produced
and COMBO object #ID within A901 field.

bottom rows, left column of four entries:
R     = R-band total object magnitude in Vega system
z     = mean and rms of the redshift PDF of the likely object class
z_g,q = Maximum-Likelihood redshift for galaxy and QSO interpretation
class   Unique choices are 'Star', 'White Dwarf', 'Galaxy', 'QSO'
        further choices are explained in Gray et al. (2008)

bottom rows, right column of four entries:
x / y = position on co-added R-band image in arcsec
chi^2 = reduced Chi^2 for best fit in each class (star,gal,QSO,WD);
        values above ~40 are set to 99
p     = probability of class membership for star/galaxy/QSO/WD
        based on SED fits and I-band magnitude priors
A x B = SExtractor's object FWHM normalised to PSF = 1.0 x 1.0
        measured on co-added R-band image

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