J/ApJS/282/14 Green Peas from SDSS DR18 (Samonski+, 2026)
Highly efficient identification of extreme emission-line galaxies in the local
universe: >8000 new Green Pea candidates at 0.12<z<0.36.
Samonski H., Salim S., Salzer J.J.
<Astrophys. J. Suppl. Ser., 282, 14 (2026)>
=2026ApJS..282...14S 2026ApJS..282...14S
ADC_Keywords: Galaxies, spectra; Equivalent widths; Optical; Photometry;
Galaxies, radius; Redshifts; Surveys
Keywords: Emission line galaxies
Abstract:
The currently known compact extreme emission-line galaxies (the "Green
Peas" (GPs)) in the Sloan Digital Sky Survey (SDSS) are rare and were
mostly found among serendipitous spectroscopic targets, thus leaving
open the possibility that a substantial population of GPs is missed. A
significantly larger number of identified GPs in the Local Universe
might provide a better characterization of their high-redshift analogs
and Lyman continuum escape. In this paper, we confront the challenges
of robustly identifying GPs without spectroscopic information, a
needed approach considering the incompleteness of spectroscopic
surveys for compact sources. The principal difficulty stems from a
significant contamination of photometric candidates by stars and
quasars of similar color. To solve this, we introduce a spectral
energy distribution matching method, which separates candidate GPs
from contaminants on the basis of SDSS and Wide-field Infrared Survey
Explorer photometry of spectroscopically confirmed stars, quasars, and
galaxies. The method has an effectiveness of 85% and a contamination
rate of ∼10%. With it, we identify ∼9600 GP candidates expected to lie
in the 0.12<z<0.36 range-a tenfold increase over what would be
selected using SDSS DR18 spectra. Some of the new GPs are as bright as
r∼19, and 1200 are predicted to have [OIII]5007 equivalent widths in
excess of 500Å. The new population contains many "Extended Peas,"
which are absent among known GPs and possibly represent merging
systems. We provide catalogs containing 8313 newly identified GP
candidates, as well as 917 GPs confirmed using SDSS spectroscopy and
521 GPs with spectroscopic redshifts from LAMOST and other sources.
Description:
Our selection is based on the SDSS Data Release 18 (DR18) photometric
and spectroscopic data (Almeida+ 2023ApJS..267...44A 2023ApJS..267...44A). We also use
[OIII]5007 EWs from the MPA-JHU catalog, as provided in the DR18
database (table galSpecLine). All EWs in this work refer to the rest
frame. As is the usual practice regarding EWs, no correction for
internal dust is applied to it.
We combine the SDSS photometry with the photometry from the Wide-Field
Infrared Survey Explorer (WISE).
Specifically, we utilize the unWISE catalog (Lang+ 2016; see II/363),
available from the SDSS database (table wiseForcedTarget), which
provides photometry for 400 million sources where SDSS positions and
light profiles served as modeling priors.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table5.dat 81 917 Green Peas confirmed with SDSS DR18 spectroscopy
table6.dat 83 521 Green Peas confirmed with non-SDSS spectroscopy
table7.dat 69 8313 Green Pea candidates (no spectroscopic confirmation)
--------------------------------------------------------------------------------
See also:
VII/241 : The 2dF QSO Redshift Survey (Croom+ 2004)
VII/260 : The SDSS-DR7 quasar catalog (Schneider+, 2010)
II/363 : The band-merged unWISE Catalog (Schlafly+, 2019)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
VII/289 : SDSS quasar catalog, sixteenth data release (DR16Q) (Lyke+, 2020)
I/356 : Gaia DR3 Part 2. Extra-galactic (Gaia Collaboration, 2022)
V/162 : LAMOST DR11 catalogs (Luo+, 2026)
J/MNRAS/372/425 : 2dF-SDSS Luminous Red Galaxy Survey, 2SLAQ (Cannon+, 2006)
J/AJ/143/145 : Emission-line objects from ALFALFA Ha survey (Kellar+, 2012)
J/ApJ/765/26 : Very low-z SDSS galaxies with Hα emission (Shim+, 2013)
J/A+A/578/A105 : EELGs out to z∼1 in zCOSMOS (Amorin+, 2015)
J/ApJ/819/110 : Extremely metal-poor gal. in SDSS. II. (Sanchez Almeida+ 2016)
J/ApJ/844/171 : Lyα profile in 43 Green Pea galaxies (Yang+, 2017)
J/ApJ/847/38 : Extreme emission line galaxies at z≲0.05 (Yang+, 2017)
J/ApJ/860/83 : Extreme [OIII] emitters at z∼0.5 from SDSS-DR14 (Li+, 2018)
J/AJ/160/242 : The Hα dots survey. II. 119 new dots (Salzer+, 2020)
J/A+A/668/A60 : Extreme emission line gal. in J-PLUS (Lumbreras-Calle+, 2022)
J/ApJS/267/16 : Strong [OIII]5007 emission-line compact galaxies (Liu+, 2023)
J/A+A/674/A210 : Starburst galaxy UM 462 datacube (Monreal-Ibero+, 2023)
J/ApJ/960/119 : LBT-MODS opt. sp. of SDSS-FIRST galaxies (Bhat+, 2024)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table[567].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- ID Source identifier (1)
10- 28 I19 --- objID SDSS object identifier
30- 40 F11.7 deg RAdeg SDSS DR18 Right Ascension (J2000)
42- 52 F11.7 deg DEdeg [-23.1/82] SDSS DR18 Declination (J2000)
54- 58 F5.2 mag rmag [17.5/22] SDSS DR18 apparent r band AB
magnitude
60- 64 F5.2 arcsec R50 [0.36/1.4]?=-9 SDSS DR18 half-light radius
66- 69 F4.2 [0.1nm] logEW [2.2/3.6] log [OIII]5007Å equivalent width;
Angstroms
71- 76 F6.4 --- z [0.13/0.41]? Spectroscopic redshift
(not for table 7)
78- 83 A6 --- r_z Source of z (2)
--------------------------------------------------------------------------------
Note (1): GP-S stands for Green Pea SDSS, GP-N stands for Green Pea Non-SDSS,
GP-C stands for Green Pea Candidate.
Note (2): Reference of z (see Section 6) as follows:
SDSS = SDSS DR18 (917 occurrences for table 5)
LAMOST = LAMOST DR10 LRS v2.0 database (384 occurrences)
SIMBAD = (84 occurrences)
GAIA = Gaia Galaxy Candidates Catalog, see I/356 (51 occurrences)
B20 = Brunker+ 2020ApJ...898...68B 2020ApJ...898...68B (2 occurrences)
--------------------------------------------------------------------------------
History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 10-Jul-2026