A Critical Assessment of Photometric Redshift Methods: A CANDELS Investigation
Abstract
We present results from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) photometric redshift methods investigation. In this investigation, the results from eleven participants, each using a different combination of photometric redshift code, template spectral energy distributions (SEDs) and priors, are used to examine the properties of photometric redshifts applied to deep fields with broad-band multi-wavelength coverage. The photometry used includes U-band through mid-infrared filters and was derived using the TFIT method. Comparing the results, we find that there is no particular code or set of template SEDs that results in significantly better photometric redshifts compared to others. However, we find codes producing the lowest scatter and outlier fraction utilize a training sample to optimize photometric redshifts by adding zero-point offsets, template adjusting or adding extra smoothing errors. These results therefore stress the importance of the training procedure. We find a strong dependence of the photometric redshift accuracy on the signal-to-noise ratio of the photometry. On the other hand, we find a weak dependence of the photometric redshift scatter with redshift and galaxy color. We find that most photometric redshift codes quote redshift errors (e.g., 68% confidence intervals) that are too small compared to that expected from the spectroscopic control sample. We find that all codes show a statistically significant bias in the photometric redshifts. However, the bias is in all cases smaller than the scatter, the latter therefore dominates the errors. Finally, we find that combining results from multiple codes significantly decreases the photometric redshift scatter and outlier fraction. We discuss different ways of combining data to produce accurate photometric redshifts and error estimates.
Keywords
Cite
@article{arxiv.1308.5353,
title = {A Critical Assessment of Photometric Redshift Methods: A CANDELS Investigation},
author = {Tomas Dahlen and Bahram Mobasher and Sandra M. Faber and Henry C. Ferguson and Guillermo Barro and Steven L. Finkelstein and Kristian Finlator and Adriano Fontana and Ruth Gruetzbauch and Seth Johnson and Janine Pforr and Mara Salvato and Tommy Wiklind and Stijn Wuyts and Viviana Acquaviva and Mark E. Dickinson and Yicheng Guo and Jiasheng Huang and Kuang-Han Huang and Jeffrey A. Newman and Eric F. Bell and Christopher J. Conselice and Audrey Galametz and Eric Gawiser and Mauro Giavalisco and Norman A. Grogin and Nimish Hathi and Dale Kocevski and Anton M. Koekemoer and David C. Koo and Kyoung-Soo Lee and Elizabeth J. McGrath and Casey Papovich and Michael Peth and Russell Ryan and Rachel Somerville and Benjamin Weiner and Grant Wilson},
journal= {arXiv preprint arXiv:1308.5353},
year = {2015}
}
Comments
26 pages, 15 figures, ApJ in press