TITLE:
Precision photometric redshift calibration for galaxy-galaxy weak lensing.
AUTHOR(S):
R. Mandelbaum, U. Seljak, C. M. Hirata, S. Bardelli, M. Bolzonella, A. Bongiorno, M. Carollo, T. Contini, C. E. Cunha, B. Garilli, A. Iovino, P.
Kampczyk, J.-P. Kneib, C. Knobel, D. C. Koo, F. Lamareille, O. Le Fevre, J.-F. Leborgne, S. J. Lilly, C. Maier, V. Mainieri, M. Mignoli, J. A. Newman,
P. A. Oesch, E. Perez-Montero, E. Ricciardelli, M. Scodeggio, J. Silverman, L. Tasca.
DATE:
2007 Sep 11 (MNRAS, submitted); 2007 Sep 11 (arXiv, posted, v1); 2007 Sep 12 (arXiv, posted, v2);
2007 Dec 21 (revised); 2007 Dec 21 (arXiv, posted, v3);
2008 Jan 10 (MNRAS, accepted);
2008 Apr 10 (MNRAS, published).
AVAILABILITY:
arXiv 0709.1692 (free);
Blackwell Synergy (requires subscription).
PUBLICATION INFORMATION:
Mon. Not. R. Astron. Soc. 386, 781--806 (2008).
ABSTRACT:
Accurate photometric redshifts are among the key requirements for precision weak lensing measurements. Both the large size of the Sloan Digital Sky
Survey (SDSS) and the existence of large spectroscopic redshift samples that are flux-limited beyond its depth have made it the optimal data source for
developing methods to properly calibrate photometric redshifts for lensing. Here, we focus on galaxy-galaxy lensing in a survey with spectroscopic lens
redshifts, as in the SDSS. We develop statistics that quantify the effect of source redshift errors on the lensing calibration and on the weighting
scheme, and show how they can be used in the presence of redshift failure and sampling variance. We then demonstrate their use with 2838 source
galaxies with spectroscopy from DEEP2 and zCOSMOS, evaluating several public photometric redshift algorithms, in two cases including a full p(z) for
each object, and find lensing calibration biases as low as 1% (due to fortuitous cancellation of two types of bias) or as high as 20% for methods in
active use (despite the small mean photoz bias of these algorithms). Our work demonstrates that lensing-specific statistics must be used to reliably
calibrate the lensing signal, due to asymmetric effects of (frequently non-Gaussian) photoz errors. We also demonstrate that large-scale structure
(LSS) can strongly impact the photoz calibration and its error estimation, due to a correlation between the LSS and the photoz errors, and argue that
at least two independent degree-scale spectroscopic samples are needed to suppress its effects. Given the size of our spectroscopic sample, we can
reduce the galaxy-galaxy lensing calibration error well below current SDSS statistical errors.
ADS BIBLIOGRAPHIC CODE: 2008MNRAS.386..781M
COMMENTS: N/A.