Photo-z Quality Cuts and their Effect on the Measured Galaxy Clustering

Abstract

Photometric galaxy surveys are an essential tool to further our understanding of the large-scale structure of the universe, its matter and energy content and its evolution. These surveys necessitate the determination of the galaxy redshifts using photometric techniques (photo-z). Oftentimes, it is advantageous to remove from the galaxy sample those for which one suspects that the photo-z estimation might be unreliable. In this paper, we show that applying these photo-z quality cuts blindly can grossly bias the measured galaxy correlations within and across photometric redshift bins. We then extend the work of Ho et al. (2012) and Ross et al. (2011) to develop a simple and effective method to correct for this using the data themselves. Finally, we apply the method to the Mega-Z catalog, containing about a million luminous red galaxies in the redshift range 0.45 < z < 0.65. After splitting the sample into four Δz = 0.05 photo-z bins using the BPZ algorithm, we see how our corrections bring the measured galaxy auto- and cross-correlations into agreement with expectations. We then look for the BAO feature in the four bins, with and without applying the photo-z quality cuts, and find a broad agreement between the BAO scales extracted in both cases. Intriguingly, we observe a correlation between galaxy density and photo-z quality even before any photo-z quality cuts are applied. This may be due to uncorrected observational effects that result in correlated gradients across the sky of the galaxy density and the galaxy photo-z precision. Our correction procedure could also help to mitigate some of these systematic effects.

Final version, accepted for publication at MNRAS. 17 pages, 15 figures, 2 tables

References in corpus (14)

• Planck 2013 results. XVI. Cosmological parameters
• EAZY: A Fast, Public Photometric Redshift Code
• Measuring the Baryon Acoustic Oscillation scale using the SDSS and 2dFGRS
• Galaxies in the Hubble Ultra Deep Field: I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology
• TPZ : Photometric redshift PDFs and ancillary information by using prediction trees and random forests
• Large-Scale Anisotropic Correlation Function of SDSS Luminous Red Galaxies
• The 2dF-SDSS LRG and QSO (2SLAQ) Luminous Red Galaxy Survey
• Clustering of luminous red galaxies I: large scale redshift space distortions
• MegaZ-LRG: A photometric redshift catalogue of one million SDSS Luminous Red Galaxies
• Error analysis in cross-correlation of sky maps: application to the ISW detection
• Tracing The Sound Horizon Scale With Photometric Redshift Surveys
• Excess Clustering on Large Scales in the MegaZ DR7 Photometric Redshift Survey
• First Cosmological Constraints on Dark Energy from the Radial Baryon Acoustic Scale
• Photometric redshifts: estimating their contamination and distribution using clustering information

Cited by in corpus (8)

• Photometric redshift analysis in the Dark Energy Survey Science Verification data
• SOMz: photometric redshift PDFs with self organizing maps and random atlas
• Galaxy clustering, photometric redshifts and diagnosis of systematics in the DES Science Verification data
• The PAU Survey: Early demonstration of photometric redshift performance in the COSMOS field
• Precise photometric redshifts with a narrow-band filter set: The PAU Survey at the William Herschel Telescope
• The PAU Survey: Photometric redshifts using transfer learning from simulations
• Assessing the photometric redshift precision of the S-PLUS survey: the Stripe-82 as a test-case
• Galaxy clustering with photometric surveys using PDF redshift information