J/A+A/525/A157 SDSS automated morphology classification (Huertas-Company+, 2011)
Revisiting the Hubble sequence in the SDSS DR7 spectroscopic sample:
a publicly available Bayesian automated classification.
Huertas-Company M., Aguerri J.A.L., Bernardi M., Mei S., Sanchez Almeida J.
<Astron. Astrophys. 525, A157 (2011)>
=2011A&A...525A.157H 2011A&A...525A.157H
ADC_Keywords: Surveys ; Galaxies, spectra ; Morphology
Keywords: catalogs - astronomical databases: miscellaneous -
Galaxy: fundamental parameters - galaxies: evolution -
Galaxy: formation
Abstract:
We present an automated morphological classification in 4 types (E,
S0, Sab, Scd) of ∼700 000 galaxies from the SDSS DR7 spectroscopic
sample based on support vector machines. The main new property of the
classification is that we associate a probability to each galaxy of
being in the four morphological classes instead of assigning a single
class. The classification is therefore better adapted to nature where
we expect a continuous transition between different morphological
types. The algorithm is trained with a visual classification and then
compared to several independent visual classifications including the
Galaxy Zoo first-release catalog. We find a very good correlation
between the automated classification and classical visual ones.
Description:
We used all the SDSS DR7 spectroscopic sample as the starting base.
Then, the selection of objects was based on Sanchez Almeida et al.
(2010ApJ...714..487A 2010ApJ...714..487A) who performed an unsupervised automated
classification of all the SDSS spectra. Basically, we chose galaxies
with redshift below 0.25, and with good photometric data and clean
spectra, meaning objects not too close to the edges, not saturated, or
not properly deblended. The final catalog contains 698420 objects for
which we estimate the morphology (also available at
http://gepicom04.obspm.fr/sdss_morphology/Morphology_2010.html ).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 163 698420 Automated probabilistic morphological
classification of SDSS DR7 catalog
classes.dat 62 28 Main properties of the ASK classes (from
Sanchez Alemida et al., 2010ApJ...714..487A 2010ApJ...714..487A)
catalog.fit 2880 21345 FITS file of the catalog
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See also:
http://www.sdss.org : SDSS Home Page
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- ID [1,699684] Sequential number
10- 27 A18 --- SpecObjID SDSS SpecObjID
29- 39 F11.7 deg RAdeg Right ascension in decimal degrees (J2000)
41- 51 E11.7 deg DEdeg Declination in decimal degrees (J2000)
53- 62 E10.7 --- z Redshift (from SDSS-DR7)
64- 72 E9.7 --- pE/S0 Probability of being early-type (E or S0)
74- 94 E21.19 --- pE Probability of being elliptical
96-116 E21.19 --- pS0 Probability of being S0 type
118-138 F21.19 --- pSab Probability of being Sa or Sb
140-160 F21.19 --- pScd Probability of being Sc or Sd
162-163 I2 --- ASK [0/27] Spectral class from Sanchez Alemida et
al. (2010ApJ...714..487A 2010ApJ...714..487A) in classes.dat file
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Byte-by-byte Description of file: classes.dat
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Bytes Format Units Label Explanations
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1- 2 I2 --- ASK [0/27] ASK Class
3 A1 --- n_ASK [*] Major class (1)
5- 10 I6 --- N Number of members in SDSS DR7
12- 15 F4.2 mag u-g SDSS u-g computed colour index (2)
17- 21 F5.2 mag g-r SDSS g-r computed colour index(2)
23- 27 F5.2 mag r-i SDSS r-i computed colour index(2)
29- 33 F5.1 0.1nm EWHb Equivalent width of Hbeta (3)
35- 39 F5.1 0.1nm EW[OIII] Equivalent width of [OIII] lambda5007 (3)
41- 45 F5.1 0.1nm EWHa Equivalent width of Halpha (3)
47- 50 F4.1 0.1nm EW[NII] Equivalent width of [N II] lambda6583 (3)
52- 54 I3 % Em Percentage of galaxies in the class with Hbeta
in emission according to the SDSS/DR7 catalog
56- 62 A7 --- Clust Clustering (Good, Neutral)
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Note (1): The asterisks denote major classes, i.e., those that altogether
include 99% of the galaxies.
Note (2): The colors have been computed from the template spectra using the
appropriate SDSS bandpasses.
Note (3): Equivalent width in the template spectra given in Aring. Negative
implies line in absorption.
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Acknowledgements:
Marc Huertas-Company, marc.huertas(at)obspm.fr
(End) Patricia Vannier [CDS] 10-Dec-2010