J/ApJS/277/41 zphot and sp. redshift for AKARI gal. in NEPW field (Kim+, 2025)
Machine learning-based photometric redshifts for galaxies in the North Ecliptic
Pole Wide field: catalogs of spectroscopic and photometric redshifts.
Kim T., Sohn J., Hwang Ho S., Ho S.C.-C., Burgarella D., Goto T.,
Hashimoto T., Jeong W.-S., Kim S.J., Malkan M.A., Miyaji T., Oi N.,
Shim H., Song H., Hwang N., Park B.-G.
<Astrophys. J. Suppl. Ser., 277, 41 (2025)>
=2025ApJS..277...41K 2025ApJS..277...41K
ADC_Keywords: Galaxies, IR; Redshifts; Photometry; Spectra, optical
Keywords: Redshift surveys ; Galaxies ; Galaxy spectroscopy
Abstract:
We perform an MMT/Hectospec redshift survey of the North Ecliptic Pole
Wide (NEPW) field covering 5.4deg2 and use it to estimate the
photometric redshifts for the sources without spectroscopic redshifts.
By combining 2572 newly measured redshifts from our survey with
existing data from the literature, we create a large sample of 4421
galaxies with spectroscopic redshifts in the NEPW field. Using this
sample, we estimate photometric redshifts of 77,755 sources in the
band-merged catalog of the NEPW field with a random forest model. The
estimated photometric redshifts are generally consistent with the
spectroscopic redshifts, with a dispersion of 0.028, an outlier
fraction of 7.3%, and a bias of -0.01. We find that the standard
deviation of the prediction from each decision tree in the random
forest model can be used to infer the fraction of catastrophic
outliers and the measurement uncertainties. We test various
combinations of input observables, including colors and magnitude
uncertainties, and find that the details of these various combinations
do not change the prediction accuracy much. As a result, we provide a
catalog of 77,755 sources in the NEPW field, which includes both
spectroscopic and photometric redshifts up to z∼2.
Description:
The basement for our photometric redshift measurement is multiband
photometry of the sources in the North Ecliptic Pole Wide (NEPW)
field. AKARI observes the NEPW field with its nine filters in the NIR
and MIR ranges (e.g., N2, N3, and N4) (Matsuhara+ 2006PASJ...58..673M 2006PASJ...58..673M;
Lee+ 2009PASJ...61..375L 2009PASJ...61..375L; Kim+ 2012, J/A+A/548/A29) and detects
91681 sources. Based on the AKARI observations, our team constructs
the band-merged catalog for the NEPW field (Kim+ 2021, J/MNRAS/500/4078)
by crossmatching the sources detected in AKARI NEPW surveys and other
follow-up observations. See Section 2.1. for further explanations on
photometric bands used for photometric redshift estimations.
We compile spectroscopic redshifts from the previous observations.
See Section 2.2.
We also add new spectroscopic redshifts based on our own spectroscopic
observations for the NEPW field.
We conduct our own spectroscopic survey with MMT/Hectospec. Our survey
was carried out from 2020 to 2022 as a part of the K-GMT science
program (PI: Ho Seong Hwang). Hectospec is a multiobject optical
spectrograph with 300 fed fibers for MMT. It covers the wavelength
range of 3500-10000Å with a spectral resolution of R∼1000-2000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 74 91861 Redshifts in the NEPW field
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See also:
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/ApJS/172/583 : NEP source catalog (Hwang+, 2007)
J/ApJS/190/166 : Optical catalog of AKARI NEP-wide survey (Jeon+, 2010)
J/A+A/514/A5 : PAH luminous galaxies at z∼1 (Takagi+, 2010)
J/A+A/548/A29 : IR source catalog of AKARI NEP-Wide field (Kim+, 2012)
J/ApJS/207/37 : IR sources spectroscopy in the AKARI NEP (Shim+, 2013)
J/ApJS/214/20 : AKARI NEP field J- and H- band source catalog (Jeon+, 2014)
J/A+A/566/A60 : Optical-NIR catalog of AKARI NEP Deep Field (Oi+, 2014)
J/MNRAS/446/911 : X-ray sources in the AKARI NEP deep field (Krumpe+, 2015)
J/ApJS/224/24 : The COSMOS2015 catalog (Laigle+, 2016)
J/ApJS/234/38 : Spitzer/IRAC obs. of the NEP (Nayyeri+, 2018)
J/A+A/641/A129 : Multi-band photometry catalog of 185 DSFGs (Barrufet+, 2020)
J/MNRAS/498/609 : AKARI North Ecliptic Pole field in u-band (Huang+, 2020)
J/MNRAS/500/4078 : Band-merged catalogue of AKARI infrared sources (Kim+, 2021)
J/A+A/651/A108 : AGN cat. from the AKARI NEP Wide field (Poliszczuk+, 2021)
J/A+A/651/A55 : Predicted redshifts of galaxies with NetZ (Schuldt+, 2021)
J/ApJ/945/94 : HectoMAP: the complete redshift survey (DR2) (Sohn+, 2023)
J/A+A/689/A83 : Chandra source identifications in AKARI NEPD (Miyaji+, 2024)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID [2/135155] Identifier (1)
8- 16 F9.5 deg RAdeg [266.6/273.5] Right Ascension (J2000)
18- 25 F8.5 deg DEdeg [65.2/67.8] Declination (J2000)
27- 32 F6.3 mag rmag [14.47/]?=99 Apparent r-band magnitude
34- 40 F7.4 --- specz [-0.013/3.9]? Spectroscopic redshift
42- 47 F6.4 --- e_specz [0.0001/0.0007]? Uncertainty in specz (2)
49 I1 --- Source [1/9] Source of specz (3)
51- 55 F5.2 --- r-value [4.0/49.11]? r-value in specz measurement (2)
57- 62 F6.4 --- photz [0.02/1.7]? Photometric redshift measured
using ML in this study
64- 69 F6.4 --- e_photz [0.008/0.2]? Uncertainty in photz (2)
71- 74 F4.2 --- sigmaDT [0/0.72]? Standard deviation of the decision
trees (See Section 3.4)
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Note (1): ID listed in the AKARI NEPW catalog of Kim+ 2021, J/MNRAS/500/4078
Note (2): The errors and r-values associated with spectroscopic redshift are
written only when they are measured using RVSNUpy.
Note (3): Source as follows:
1 = Kim+ 2021, J/MNRAS/500/4078
2 = This study
9 = No specz
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 18-Nov-2025