J/ApJS/272/42 COSMOS2020 galaxy morphology classif. with USmorph (Song+, 2024)
USmorph: an updated framework of automatic classification of galaxy morphologies
and its application to galaxies in the COSMOS field.
Song J., Fang G., Ba S., Lin Z., Gu Y., Zhou C., Wang T., Hao C.-N.,
Liu G., Zhang H., Yao Y., Kong Xu
<Astrophys. J. Suppl. Ser., 272, 42 (2024)>
=2024ApJS..272...42S 2024ApJS..272...42S
ADC_Keywords: Galaxies, optical; Photometry, HST; Redshifts; Morphology
Keywords: Galaxy structure ; Astrostatistics techniques ;
Astronomy data analysis
Abstract:
Morphological classification conveys abundant information on the
formation, evolution, and environment of galaxies. In this work, we
refine a two-step galaxy morphological classification framework
(USmorph), which employs a combination of unsupervised
machine-learning and supervised machine-learning techniques, along
with a self-consistent and robust data-preprocessing step. The updated
method is applied to galaxies with Imag<25 at 0.2<z<1.2 in the COSMOS
field. Based on their Hubble Space Telescope/Advanced Camera for
Survey I-band images, we classify them into five distinct
morphological types: spherical (SPH, 15200), early-type disk (17369),
late-type disk (21143), irregular disk (IRR, 28965), and unclassified
(UNC, 17129). In addition, we have conducted both parametric and
nonparametric morphological measurements. For galaxies with stellar
masses exceeding 109M☉, a gradual increase in effective radius
from SPHs to IRRs is observed, accompanied by a decrease in the Sersic
index. Nonparametric morphologies reveal distinct distributions of
galaxies across the Gini-M20 and C-A parameter spaces for different
categories. Moreover, different categories exhibit significant
dissimilarity in their G2 and Ψ distributions. We find
morphology to be strongly correlated with redshift and stellar mass.
The consistency of these classification results with expected
correlations among multiple parameters underscores the validity and
reliability of our classification method, rendering it a valuable tool
for future studies.
Description:
In this work, we conduct a pilot study for the Chinese Space Station
Telescope (CSST) to validate the reliability of the algorithm
developed by Zhou+ (2022AJ....163...86Z 2022AJ....163...86Z) and Fang+ (2023AJ....165...35F 2023AJ....165...35F)
with COSMOS I-band images, since these images are high resolution and
similar to the imaging data of the CSST.
The high-resolution images captured by the Hubble Space Telescope
(HST)/Advanced Camera for Surveys (ACS) in the F814W filter are
capitalized, encompassing an area of roughly 1.64deg2 within the
COSMOS field. The original images comprise approximately
590 pointings, with an average exposure time of 2028s per pointing.
These images were meticulously processed by
Koekemoer+ (2007ApJS..172..196K 2007ApJS..172..196K) , resulting in images with a pixel
scale of 0.03" and a 5σ depth of 27.2 AB mag within a 0.24"
diameter aperture.
The sample utilized in this study is constructed based on the "Farmer"
COSMOS2020 catalog (Weaver+ 2022, J/ApJS/258/11), which provides
comprehensive photometric information spanning 35 bands from
ultraviolet to near-infrared. See Section 2.2.
Throughout this work, we adopt a flat Lambda cold dark matter
(ΛCDM) cosmology with H0=70km/s/Mpc, Ωm=0.3, and
ΩΛ=0.7, along with a Chabrier (2003PASP..115..763C 2003PASP..115..763C)
initial mass function.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 130 99806 Final catalog
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See also:
VII/265 : COSMOS Morphological Catalog (V1.1) (Tasca+ 2009)
J/ApJS/147/1 : Classification of nearby galaxies (Conselice+, 2003)
J/AJ/128/163 : Galaxy morphological classification (Lotz+, 2004)
J/A+A/468/937 : NIR AO imaging in COSMOS deep field (Huertas-Company+, 2007)
J/AJ/136/773 : Classical bulge & pseudobulge structures (Fisher+, 2008)
J/ApJ/690/1236 : COSMOS photometric redshift catalog (Ilbert+, 2009)
J/MNRAS/410/166 : Morphological types from Galaxy Zoo 1 (Lintott+, 2011)
J/MNRAS/428/1460 : Massive early-type galaxies (Buitrago+, 2013)
J/MNRAS/440/843 : SIM2D parameters of SDSS-DR7 galaxies (Omand+, 2014)
J/ApJS/224/24 : The COSMOS2015 catalog (Laigle+, 2016)
J/A+A/631/A38 : Local galaxies dust properties (Lianou+, 2019)
J/A+A/664/A92 : GAMA. MegaMorp/GalfitM profile fits (Haeussler+, 2022)
J/ApJS/258/11 : The COSMOS2020 catalog (Weaver+, 2022)
J/ApJS/268/34 : Morphology of COSMOS -UltraVISTA -DASH galaxies (Dai+, 2023)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- Seq [1/99806] Sequential number identifier
7- 15 F9.5 deg RAdeg [149.4/150.8] Right Ascension (J2000)
(ALPHAJ2000) (1)
17- 23 F7.5 deg DEdeg [1.6/2.9] Declination (J2000) (DELTA_J2000) (1)
25- 29 F5.2 mag Imag [17.24/25] HST/ACS F814W (I-band) AB magnitude
(ACSF814WMAG) (1)
31- 34 F4.2 --- z [0.2/1.2] Redshift (lp_zBEST) (1)
36- 40 F5.2 [Msun] logMs [6/13.3] Log of stellar mass (lpmassbest) (1)
42- 47 F6.2 kpc Reff [0.03/99.2]?=-99 Effective radius at I band
49- 54 F6.2 --- n [-0/8]?=-99 Sersic index
56- 57 I2 --- Flag1 [-1/2] Flag of single Sersic fitting
(2=good fitting)
59- 62 F4.2 --- C [0/5.41] Concentration index, statmorph_csst (2)
64- 68 F5.2 --- A [-4.7/1.13] Asymmetry index, statmorph_csst (2)
70- 75 F6.2 --- S [-3.1/2]?=-99 Smoothness index (clumpiness),
statmorph_csst (2)
77- 82 F6.2 --- Gini [0.07/1]?=-99 Gini index, statmorph_csst (2)
84- 89 F6.2 --- M20 [-2.8/1]?=-99 M20 index, statmorph_csst (2)
91- 94 F4.2 --- M [0/1] Multimode index, statmorph_csst (2)
96- 99 F4.2 --- I [0/1] Intensity index, statmorph_csst (2)
101- 106 F6.2 --- D [0/2.5]?=-99 Deviation index, statmorph_csst (2)
108- 113 F6.2 --- Psi [-99/22.7]? Multiplicity, statmorph_csst,
Equation 4 (2)
115- 120 F6.2 --- G2 [0/2]?=-99 Second gradient moment,
statmorph_csst, Equation 1;
Rosa+ (2018MNRAS.477L.101R 2018MNRAS.477L.101R) (2)
122- 126 I5 --- Flag2 [0/16388] Flag of the nonparametric
morphological measurements (0=good measurement)
128- 130 A3 --- Class Derived galaxy morphological type (3)
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Note (1): From the COSMOS2020 "Farmer" catalog; Weaver+ (2022, J/ApJS/258/11)
Note (2): The nonparametric measurements are described in Section 4.2.2.
Note (3): Derived galaxy morphological types as follows:
ETD = early-type disk (17369 occurrences)
IRR = irregular disk (28965 occurrences)
LTD = late-type disk (21143 occurrences)
SPH = spherical (15200 occurrences)
UNC = unclassified (17129 occurrences)
In visual inspection, SPHs exhibit a clear bulge-dominated structure,
while LTDs display a clear disk structure. ETDs show a disk structure
but have bulge components as well. IRRs include galaxies with
irregular structures or merger evidence, while galaxies that could not
be confidently identified due to poor S/N are classified as UNCs.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 27-Aug-2024