21/12/07
README file for STAGES lensing maps
contact:  Catherine Heymans // heymans [at] roe.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 STAGES weak lensing data available as part
of the STAGES public data release here:

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

A description of the lensing analysis is contained in:

C. Heymans et al:
"The dark matter environment of the Abell 901/902 supercluster: a weak lensing analysis of the HST STAGES survey"
MNRAS, 2008, 385, 1431


For further details of the STAGES 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.  MASS RECONSTRUCTIONS
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These files contain the maximum likelihood mass reconstructions of the
A901/2 STAGES supercluster as detailed in Heymans et al 2008.

The fits files are 256x256 pixels with a physical pixel scale of 7.6
arcseconds.The maps have been smoothed on a 6 pixel, or ~0.75 arcmin
scale.  They all contain WCS header information for matching with
observations.

The files are as follows:

STAGES_DMmap.fits : kappa map (E-mode)
STAGES_Bmode.fits : systematics map (B-mode)
STAGES_noise.fits : random noise map
STAGES_mask.fits  : input mask (0 = masked, 1=good, but I don't trust any pixel within a radius of 10 pixels of this mask)
STAGES_SN_DMmap.fits : Signal-to-noise kappa map, as presented in the paper
STAGES_SN_Bmode.fits : Signal-to-noise B-mode map, as presented in the paper

Luminosity/Light maps smoothed on the same scale are available on
request (heymans@roe.ac.uk).

To get a mass estimate from a given area in the kappa maps

Mass(area) = sum(kappa(area)) * Sigma_crit * pixel_area / Msun

where for A901/2 at z=0.165, 

Sigma_crit * pixel_area / Msun = 1.11212 h^{-1} 10^{12} Msun

(Equation 4 in Heymans et al 2008).  This mass is the projected
surface mass density.  You can assume that it is all associated with
the cluster at z=0.165 to an accuracy of ~5% in the cases of A901a,b
and the SW group.  For A902, there is up to 15% contamination from
CBI.

To calculate errors on the mass, we use a conservative method
combining the systematics errors (B-mode) in quadrature with the
random noise such that

Mass Error(area) = sqrt[sum(B-mode(area))**2 + sum(noise(area))**2]* Sigma_crit * pixel_area / Msun

Any questions or comments to heymans@roe.ac.uk

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