Photometric redshifts in the D3 and D4 fields

 u* = mag(dn) +25.280 -0.19 * (secZ-1)
 g' = mag(dn) +26.460 -0.12 * (secZ-1)
 r' = mag(dn) +25.978 -0.09 * (secZ-1)
 i' = mag(dn) +25.744 -0.04 * (secZ-1)
 z' = mag(dn) +24.800 -0.03 * (secZ-1)

Photometric redshifts were measured with gwynz which works with the template fitting method.

• Galaxy spectra (described here) are redshifted and then multiplied by the MegaCam filter curves (described here) to produce spectral templates ranging in type from E/S0 to active starburst and in redshift from z=0 to z=1.5.
• The galaxy photometry is converted into fluxes per unit Angstrom using the equation Where m is the magnitude, F is the flux and F₀ is the flux zeropoint of the filter in question. This produces a coarse spectral energy distribution (SED). Following flux zeropoints were used (in units of W/m²/Angstrom):

  Filter	zeropoint
  gAB	4.63e-12
  rAB	2.83e-12
  iAB	1.89e-12
  zAB	1.40e-12

• The spectral templates were compared to the SED's using the following equation:
  
  Where F_i is the flux of the galaxy, in the i-th band, σ_i is the error on the flux T_i(t,z) is the template flux for type t and redshift z, and α  is a normalization factor given by:
  
  The best matching (smallest chi-squared) template gives the redshift and galaxy type.

The figure at right shows the configuration. The red lines show the outlines of the MegaCam CCD's. The blue dots and green dots show the location of galaxies with spectroscopic redshifts from DEEP and CFRS respectively.

The DEEP+CFRS catalog was cross referenced with the photometric redshift catalog. For each DEEP or CFRS object, the closest and second closest CFHTLS was found. If the closest CFHTLS object was within 2 arcseconds it was deemed a good match unless there was a second object within 4 arcseconds (this second criteria was to avoid confusion in the case of two nearby galaxies).

Inset into the upper left corner is a plot of the spectral energy distribution (flux vs. wavelength) of this galaxy. In this inset, the red dots with errorbars show the griz-band data converted to an SED and the red line shows the best fitting template, determined by the photometric redshift chi-squared minimization process. The blue line shows the best fitting template, but this time constrained to be at the spectroscopic redshift.

(Clicking on one of the black dots will highlight it and produce a similiar figure but with the SED of the selected galaxy plotted in the inset.)

No spectroscopic data is available in the D4 field is available, so no checks have been made. Since the photometric offsets seem to be different between the two fields (as discussed here) the photometric redshifts for the D4 should be regarded with suspicion.

 # x y RA Dec gMega err rMega err iMega err zMega err CCD z_phot type_phot a_phot 

• x and y refer to the stacked images.
• RA and Dec were computed using the CCD x,y coordinates and Dave Balam's astrometric solutions.
• gMega, rMega, iMega and zMega are the Kron magnitudes (SExtractor's MAG_AUTO), with their uncertainties for the galaxy. The apertures are all determined in z-band. Only objects detected in all four bands are included (3 filter photometric redshifts are very unreliable, except for the special case of Lyman break galaxies).
• CCD is the MegaCam chip number.
• z_phot is photometric redshift.
• type_phot gives the file name of the matching spectra template, as listed here
• a_phot is the normalization factor required to match the template to the data.

• D3griz.zed
• D4griz.zed