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Can We Detect the Color–Density Relation with Photometric Redshifts?

Lai, C.-C.; Lin, L.; Jian, H.-Y.; Chiueh, T.-H.; Merson, A.; Baugh, C.M.; Foucaud, S.; Chen, C.-W.; Chen, W.-P.

Can We Detect the Color–Density Relation with Photometric Redshifts? Thumbnail


C.-C. Lai

L. Lin

H.-Y. Jian

T.-H. Chiueh

A. Merson

S. Foucaud

C.-W. Chen

W.-P. Chen


A variety of methods have been proposed to define and to quantify galaxy environments. While these techniques work well in general with spectroscopic redshift samples, their application to photometric redshift surveys remains uncertain. To investigate whether galaxy environments can be robustly measured with photo-z samples, we quantify how the density measured with the nearest-neighbor approach is affected by photo-z uncertainties by using the Durham mock galaxy catalogs in which the 3D real-space environments and the properties of galaxies are known exactly. Furthermore, we present an optimization scheme in the choice of parameters used in the 2D projected measurements that yield the tightest correlation with respect to the 3D real-space environments. By adopting the optimized parameters in the density measurements, we show that the correlation between the 2D projected optimized density and the real-space density can still be revealed, and the color–density relation is also visible out to z ~ 0.8 even for a photo-z uncertainty (${\sigma }_{{{\rm{\Delta }}}_{z}/(1+z)}$) up to 0.06. We find that at redshifts 0.3 < z < 0.5 a deep (i ~ 25) photometric redshift survey with ${\sigma }_{{{\rm{\Delta }}}_{z}/(1+z)}\;=\;0.02$ yields a performance in small-scale density measurement that is comparable to a shallower i ~ 22.5 spectroscopic sample with ~10% sampling rate. Finally, we discuss the application of the local density measurements to the Pan-STARRS1 Medium Deep Survey (PS-MDS), one of the largest deep optical imaging surveys. Using data from ~5 square degrees of survey area, our results show that it is possible to measure local density and to probe the color–density relation with 3σ confidence level out to z ~ 0.8 in the PS-MDS. The color–density relation, however, quickly degrades for data covering smaller areas.


Lai, C., Lin, L., Jian, H., Chiueh, T., Merson, A., Baugh, C., …Chen, W. (2016). Can We Detect the Color–Density Relation with Photometric Redshifts?. Astrophysical Journal, 825(1), Article 40.

Journal Article Type Article
Acceptance Date May 1, 2016
Online Publication Date Jun 27, 2016
Publication Date Jul 1, 2016
Deposit Date Aug 18, 2016
Publicly Available Date Aug 23, 2016
Journal Astrophysical Journal
Print ISSN 0004-637X
Electronic ISSN 1538-4357
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 825
Issue 1
Article Number 40


Published Journal Article (7.2 Mb)

Copyright Statement
© 2016. The American Astronomical Society. All rights reserved.

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