J/MNRAS/485/1085 Classification of emission-line galaxies (Stampoulis+, 2019)
Multidimensional data-driven classification of emission-line galaxies.
Stampoulis V., van Dyk D.A., Kashyap V.L., Zezas A.
<Mon. Not. R. Astron. Soc., 485, 1085-1102 (2019)>
=2019MNRAS.485.1085S 2019MNRAS.485.1085S (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Galaxy catalogs ; Spectroscopy ; Optical
Keywords: galaxies: active - galaxies: clusters - galaxies: emission lines
Abstract:
We propose a new soft clustering scheme for classifying galaxies in
different activity classes using simultaneously four emission-line
ratios: log([NII]/Hα), log([SII]/Hα), log([OI]/Hα),
and log([OIII]/Hβ). We fit 20 multivariate Gaussian distributions
to the four-dimensional distribution of these lines obtained from the
Sloan Digital Sky Survey in order to capture local structures and
subsequently group the multivariate Gaussian distributions to
represent the complex multidimensional structure of the joint
distribution of galaxy spectra in the four-dimensional line ratio
space. The main advantages of this method are the use of all four
optical-line ratios simultaneously and the adoption of a clustering
scheme. This maximizes the use of the available information, avoids
contradicting classifications, and treats each class as a distribution
resulting in soft classification boundaries and providing the
probability for an object to belong to each class. We also introduce
linear multidimensional decision surfaces using support vector
machines based on the classification of our soft clustering scheme.
This linear multidimensional hard clustering technique shows high
classification accuracy with respect to our soft clustering scheme.
Description:
The SDSS provides an excellent resource of spectra of the central
regions (∼5.5kpc for z<0.1) of galaxies covering all different
activity types (e.g. Kauffmann et al. 2003MNRAS.346.1055K 2003MNRAS.346.1055K). For the
definition of our multidimensional activity diagnostics we use the
'galspec' data base of spectral-line measurements from the Max-Plank
Institute for Astronomy and Johns Hopkins University group. We used
the version of the catalogue made publicly available through the SDSS
Data Release 8 (Aihara et al. 2011ApJS..193...29A 2011ApJS..193...29A,
2011ApJS..195...26A 2011ApJS..195...26A; Eisenstein et al. 2011AJ....142...72E 2011AJ....142...72E), which
contains 1843200 objects.
Since the same catalogue has been used for the definition of the
two-dimensional and multidimensional diagnostics of Kauffmann et al.
(2003MNRAS.346.1055K 2003MNRAS.346.1055K) and Vogt et al. (2014ApJ...793..127V 2014ApJ...793..127V),
respectively, it is the best benchmark for testing the SoDDA. Before
proceeding with our analysis, we applied the corrections on the
line-measurement errors reported in Juneau et al.
(2014ApJ...788...88J 2014ApJ...788...88J), and we corrected the flux of the Hβ line
following Groves, Brinchmann & Walcher (2012MNRAS.419.1402G 2012MNRAS.419.1402G).
The final sample consists of 130799 galaxies, and it provides a direct
comparison with the reference diagnostics of Kauffmann et al.
(2003MNRAS.346.1055K 2003MNRAS.346.1055K) and Kewley et al. (2006MNRAS.372..961K 2006MNRAS.372..961K), which
have used very similar selection criteria.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 216 130799 Activity classification of the emission-line
galaxies in the SDSS-DR8 based on SoDDA
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See also:
https://skyserver.sdss.org/dr8 : SDSS DR8 Home Page
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- ID SDSS DR8 SpecObjID
21- 27 I7 --- Index Internal object identifier
29- 51 E23.20 [-] [NII]/Ha Logarithm of the [NII]/Hα emission
line ratio
53- 75 E23.20 [-] [SII]/Ha Logarithm of the [SII]/Hα emission
line ratio
77- 96 F20.17 [-] [OI]/Ha Logarithm of the [OI]/Hα emission
line ratio
98-120 E23.20 [-] [OIII]/Hb Logarithm of the [OIII]/Hβ emission
line ratio
122-143 E22.20 --- PSFG Probability that a galaxy belongs to the
SFG class based on the SoDDA analysis
145-166 E22.20 --- PSeyfert Probability that a galaxy belongs to the
Seyfert class based on the SoDDA analysis
168-190 E23.21 --- PLINER Probability that a galaxy belongs to the
LINER class based on the SoDDA analysis
192-214 E23.21 --- PComposite Probability that a galaxy belongs to the
composite class based on the SoDDA analysis
216 I1 --- Class [0/3] Highest-ranking activity class (1)
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Note (1): Activity class as follows:
0 = star-forming galaxies (SFG)
1 = Seyfert
2 = LINER
3 = Composite
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History:
From electronic version of the journal
(End) Ana Fiallos [CDS] 14-Sep-2022