Improved photometric redshifts with colour-constrained galaxy templates for future wide-area surveys. Issue 2 (17th July 2020)

• Record Type: Journal Article
• Authors: Lee, Bomee; Chary, Ranga-Ram
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 497:Issue 2(2020)
• Page Start: 1935
• Page End: 1945
• Publication Date: 2020-07-17
• Subjects: methods: statistical -- techniques: photometric -- galaxies: photometry; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/staa2100
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: Cosmology and galaxy evolution studies with LSST, Euclid, and Roman, will require accurate redshifts for the detected galaxies. In this study, we present improved photometric redshift estimates for galaxies using a template library that populates three-colour space and is constrained by HST /CANDELS photometry. For the training sample, we use a sample of galaxies having photometric redshifts that allows us to train on a large, unbiased galaxy sample having deep, unconfused photometry at optical-to-mid infrared wavelengths. Galaxies in the training sample are assigned to cubes in 3D colour space, V − H, I − J, and z − H . We then derive the best-fitting spectral energy distributions of the training sample at the fixed CANDELS median photometric redshifts to construct the new template library for each individual colour cube (i.e. colour-cube-based template library). We derive photometric redshifts (photo- z ) of our target galaxies using our new colour-cube-based template library and with photometry in only a limited set of bands, as expected for the aforementioned surveys. As a result, our method yields σNMAD of 0.026 and an outlier fraction of 6 per cent using only photometry in the LSST and Euclid / Roman bands. This is an improvement of ∼10 per cent on σNMAD and a reduction in outlier fraction of ∼13 per cent compared to other techniques. In particular, we improve the photo- z precision by about 30 per cent at 2 < z < 3. We also assess photo- z improvements by including K or mid-infrared bands to the ugrizYJH photometry. Our colour-cube-based template library is a powerful tool to constrain photometric redshifts for future large surveys.