Calibrating Redshift Distributions beyond Spectroscopic Limits with CrossCorrelations
Abstract
We describe a new method that can measure the true redshift distribution of any set of objects that are studied only photometrically. Measuring the angular crosscorrelation between objects in the photometric sample with objects in some spectroscopic sample as a function of the spectroscopic z, along with other, standard correlation measurements, provides sufficient information to reconstruct the redshift distribution of the photometric sample. The spectroscopic sample need not resemble the photometric sample in galaxy properties, but must fall within its sky coverage. We test this hybrid, photometricspectroscopic crosscorrelation technique with Monte Carlo simulations based on realistic error estimates (including sample variance). The rms errors in recovering both the mean redshift and σ of the redshift distribution for a single photometric redshift bin with true distribution given by a Gaussian are 1.4 × 10^{3}(σ_{z}/0.1)(Σ_{p}/10)^{0.3}(dN_{s}/dz/25,000)^{1/2}, where σ_{z} is the true Gaussian σ , Σ_{p} is the surface density of the photometric sample in galaxies arcmin ^{2}, and dN_{s}/dz is the number of galaxies with a spectroscopic redshift per unit z. We test the impact of nonGaussian redshift outliers and of systematic errors due to unaccountedfor bias evolution, errors in measuring autocorrelations, photometric zeropoint variations, or mistaken cosmological assumptions, and find that none will dominate measurement uncertainties in reasonable scenarios. The true redshift distributions of even arbitrarily faint photometric samples may be determined to the precision required by proposed dark energy experiments (Δlangzrang lesssim 3 × 10^{3} at z ~ 1) with this method.
 Publication:

The Astrophysical Journal
 Pub Date:
 September 2008
 DOI:
 10.1086/589982
 arXiv:
 arXiv:0805.1409
 Bibcode:
 2008ApJ...684...88N
 Keywords:

 galaxies: distances and redshifts;
 largescale structure of universe;
 methods: miscellaneous;
 surveys;
 Astrophysics
 EPrint:
 16 pages, including 8 figures and 2 tables