J/ApJ/962/104 Classifying intermediate-z galaxies in SDSS (Feuillet+, 2024)
Classifying intermediate-redshift galaxies in SDSS: alternative diagnostic
diagrams.
Feuillet L.M., Melendez M., Kraemer S., Schmitt H.R., Fischer T.C.,
Reeves J.N.
<Astrophys. J., 962, 104 (2024)>
=2024ApJ...962..104F 2024ApJ...962..104F
ADC_Keywords: Active gal. nuclei; Spectra, optical; Redshifts; Galaxies, Seyfert
Keywords: Active galactic nuclei ; Classification systems ; Starburst galaxies
Abstract:
We select a sample of 1437 active galactic nuclei (AGN) from the
catalog of the Sloan Digital Sky Survey galaxy properties from the
Portsmouth group by detection of the high-ionization [NeV]3426Å
emission line. We compare the fluxes of [NeIII]3869Å,
[OIII]5007Å, [OII]3726,3728Å, and [OI]6300Å to that of [NeV].
All four lines show a strong linear correlation with [NeV], although
lines from ions with lower ionization potentials have a lower
correlation coefficient. We investigate the use of two forbidden line
ratio diagnostic diagrams that do not rely on Hα in order to
classify high-redshift galaxies. These use the [NeIII]/[OII] line
ratio plotted against [OIII]/[OI] and [OIII]/[OII], respectively. We
use photoionization modeling to characterize the behavior of the
narrow-line region in AGN and star-forming regions and test the
validity of our diagnostic diagrams. We also use a luminosity cutoff
of logL[OIII][erg/s]=42, which lowers the contamination of the AGN
region by star-forming galaxies down to 10% but does not remove green
pea and purple grape galaxies from the AGN region. We also investigate
the OHNO diagram, which uses [NeIII]/[OII] plotted against
[OIII]/Hβ. Using our new diagnostic diagrams, we are able to
reliably classify AGN up to a redshift of z≤1.06 and add more than
822 new AGN to the [NeV]-selected AGN sample.
Description:
We use SDSS Data Release 12 (V/147) galaxy data extracted and made
available by the Portsmouth group (Thomas+ 2013MNRAS.431.1383T 2013MNRAS.431.1383T).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 106 2259 Final AGN sample list containing the original
[NeV] selected sample, and the previously
unclassified galaxies determined to be AGN
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/AJ/127/2002 : Star Formation Rate of NFGS galaxies (Kewley+, 2004)
J/A+A/485/657 : Physical param. of Wolf-Rayet galaxies (Brinchmann+, 2008)
J/MNRAS/383/581 : Broad-line Balmer decrements in blue AGN (Dong+, 2008)
J/MNRAS/398/1165 : AGN in nearby galaxies (Goulding+, 2009)
J/ApJ/728/38 : AEGIS: demographics of X-ray and optical AGN (Yan+, 2011)
http://www.sdss4.org/dr12/spectro/galaxy_portsmouth/ : Portsmouth group
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 12 A12 --- Type Portsmouth group BPT classification (1)
14- 18 F5.3 --- z [0.168/1.1] Galaxy spectroscopic redshift
20- 26 F7.3 deg RAdeg Right Ascension (J2000)
28- 34 F7.3 deg DEdeg [-10.81/68.3] Declination (J2000)
36- 44 E9.2 10-19W/m2/nm NeV [0/7.8e+15] The [NeV] emission line flux
(2)
46- 54 E9.2 10-19W/m2/nm NeIII [0/5.7e+9] The [NeIII] emission line flux
(2)
56- 64 E9.2 10-19W/m2/nm OI [/1.71e+18]?=-9.99 The [OI] emission line
flux (2)
66- 74 E9.2 10-19W/m2/nm OII [0/4.4e+11] The [OII] emission line flux
(2)
76- 84 E9.2 10-19W/m2/nm OIII [0/5.21e+8] The [OIII] emission line flux
(2)
86- 94 E9.2 10-19W/m2/nm Hb [0/8.24e+8] The Hβ emission line
flux (2)
96- 98 A3 --- OHNO In AGN region of OHNO diagram method
100- 102 A3 --- FLR In AGN region of 3D [OII]-FLR diagram?
104- 106 A3 --- AGN Galaxy had a [NeV] SNR>3?
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Note (1): Classification using the Baldwin, Phillips & Terlevich (BPT) diagram
as follows:
Seyfert = Seyfert galaxy (1263 occurrences)
LINER = low-ionization nuclear emission-line region (146 occurrences)
Composite = composite galaxy with both strong star formation and weak
AGN features (28 occurrences)
Unclassified = 822 occurrences
Note (2): The fluxes corrected for extinction.
Those with a valid BPT type were corrected using the Hα/Hβ
ratio, while Hβ/Hγ was used for the previously unclassified
ones. The units are 1e-17 erg/s/cm2/Angstroms.
A NULL value indicates an inf value.
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-May-2026