VII/292 DESI Legacy Imaging Surveys DR8 photometric redshifts (Duncan, 2022)
All-purpose, all-sky photometric redshifts for the
Legacy Imaging Surveys Data Release 8.
Duncan K.J.
<Mon. Not. R. Astron. Soc., 512, 3662-3683 (2022)>
=2022MNRAS.512.3662D 2022MNRAS.512.3662D (SIMBAD/NED BibCode)
=2022yCat.7292....0D 2022yCat.7292....0D
ADC_Keywords: Surveys ; Redshifts ; Optical
Keywords: catalogues - galaxies: distances and redshifts - quasars: general -
radio continuum: galaxies - X-rays: galaxies
Abstract:
We present photometric redshift (photo-z) estimates for the Dark
Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys,
currently the most sensitive optical survey covering the majority of
the extragalactic sky. Our photo-z methodology is based on a
machine-learning approach, using sparse Gaussian processes augmented
with Gaussian mixture models (GMMs) that allow regions of parameter
space to be identified and trained separately in a purely data-driven
way. The same GMMs are also used to calculate cost-sensitive learning
weights that mitigate biases in the spectroscopic training sample. By
design, this approach aims to produce reliable and unbiased
predictions for all parts of the parameter space present in wide area
surveys. Compared to previous literature estimates using the same
underlying photometry, our photo- zs are significantly less biased and
more accurate at z>1, with negligible loss in precision or
reliability for resolved galaxies at z<1. Our photo-z estimates
offer accurate predictions for rare high-value populations within the
parent sample, including optically selected quasars at the highest
redshifts (z>6), as well as X-ray or radio continuum selected
populations across a broad range of flux (densities) and redshift.
Deriving photo-z estimates for the full Legacy Imaging Surveys Data
Release 8, the catalogues provided in this work offer photo-z
estimates predicted to be of high quality for >9x108 galaxies over
∼19400deg2 and spanning 0<z<7, offering one of the most
extensive samples of redshift estimates ever produced.
Description:
The photometric redshift catalogues are separated into Legacy Survey
North (MzLS + BASS photometry) and South (DeCaLS photometry). Object
identifier information necessary to match sources with corresponding
DR8 photometry are provided (release, brickid, objid), as well as
derived photometric redshifts and recommended data and redshift
quality flags.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
north/* . 123 Legacy Surveys DR8 North Photometric Redshifts
files (323 213 867 sources)
south/* . 349 Legacy Surveys DR8 South Photometric Redshifts
files (1 252 523 992 sources)
--------------------------------------------------------------------------------
See also:
https://www.legacysurvey.org/dr8 : DESI DR8 Home Page
Byte-by-byte Description of file: north/* south/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 I16 --- id Unique object identifier combining release,
brickid and objid (id)
18- 21 I4 --- release LS DR8 release number - denoting the camera
and filter set used (release)
23- 28 I6 --- brickid LS DR8 brick number (brickid)
30- 34 I5 --- objid LS DR 8 catalogue object number within
this brick (objid)
36- 51 F16.12 deg RAdeg Right Ascension (J2000.0) (ra)
52- 67 F16.12 deg DEdeg Declination (J2000.0) (dec)
69- 72 A4 --- type Optical morphological model:
PSF, REX, DEV, EXP or COMP (type) (1)
74- 78 F5.3 --- pstar ? Star likelihood based on colours from GMM
star-QSO classification (pstar)
80- 81 A2 --- gmmcomp Best-matching GMM component used to derive
photo-z estimate (gmmcomp)
83- 88 F6.3 --- zphot Photo-z estimate - mean of the normally
distributed photo-z posterior (zphot)
90- 95 F6.3 --- e_zphot ? Uncertainty on zphot - standard deviation
of the normally distributed photo-z posterior
(zphot_err)
97 I1 --- fclean ? Photometry reliability flag, =1 for sources
free of blending or imaging artefacts
(flag_clean)
99 I1 --- fqual Photo-z reliability flag, =1 for sources
expected to have well-constrained estimates
and 'flag_clean = 1' (flag_qual)
--------------------------------------------------------------------------------
Note (1): Type as follows:
PSF = stellar
REX = round exponential galaxy
DEV = de Vaucouleurs
EXP = exponential
COMP = composite
--------------------------------------------------------------------------------
Acknowledgements:
Kenneth Duncan, kdun(at)roe.ac.uk
(End) Patricia Vannier [CDS] 16-Jun-2022