J/A+A/695/A106 Abell 194 low-surface-brightness galaxies (Thuruthipilly+, 2025)
DES to HSC: Detecting low-surface-brightness galaxies in the Abell 194 cluster
using transfer learning.
Thuruthipilly H., Junais , Koda J., Pollo A., Yagi M., Yamanoi H.,
Komiyama Y., Romano M., Malek K., Donevski D.
<Astron. Astrophys. 695, A106 (2025)>
=2025A&A...695A.106T 2025A&A...695A.106T (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, photometry ; Optical ; Surveys ; Morphology
Keywords: methods: data analysis - methods: observational -
techniques: image processing - catalogs - galaxies: dwarf -
galaxies: evolution
Abstract:
Low surface brightness galaxies (LSBGs) are important for
understanding galaxy evolution and cosmological models. The upcoming
large-scale surveys are expected to uncover a large number of LSBGs,
requiring accurate automated or machine learning-based methods for
their detection.
We study the scope of transfer learning for the identification of
LSBGs. We used transformer models trained on Dark Energy Survey (DES)
data to identify LSBGs from dedicated Hyper Suprime-Cam (HSC)
observations of the Abell 194 cluster, which are two magnitudes deeper
than DES. A new sample of LSBGs and ultra-diffuse galaxies (UDGs)
around Abell 194 was compiled, and their properties were investigated.
We used eight models, divided into two categories: LSBG Detection
Transformer (LSBG DETR) and LSBG Vision Transformer (LSBG ViT). The
data from DES and HSC were standardised based on the pixel-level
surface brightness. We used an ensemble of four LSBG DETR models and
another ensemble of four LSBG ViT models to detect LSBGs. This was
followed by a singlecomponent Sersic model fit and a final visual
inspection to filter out potential false positives and improve sample
purity.
We present a sample of 171 LSBGs in the Abell 194 cluster using HSC
data, including 87 new discoveries. Of these, 159 were identified
using transformer models, and 12 additional LSBGs were found through
visual inspection. The transformer model achieves a true positive rate
of 93% in HSC data without any fine-tuning. Among the LSBGs, 28 were
classified as UDGs. The number of UDGs and the radial UDG number
density suggests a linear relationship between UDG numbers and cluster
mass on a log scale. The UDGs share similar Sersic parameters with
dwarf galaxies and occupy the extended end of the Reff-Mg plane,
suggesting they might be an extended sub-population of dwarf galaxies.
We also found that LSBGs and UDGs near the cluster centre are brighter
and redder than those in outer regions.
We have demonstrated that transformer models trained on shallower
surveys can be successfully applied to deeper surveys with appropriate
data normalisation. This approach allows us to use existing data and
apply the knowledge to upcoming and ongoing surveys, such as the Rubin
Observatory Legacy Survey of Space and Time (LSST) and Euclid.
Description:
The Abell 194 cluster was observed with HSC using the HSC-g and HSC-r2
filters in a single pointing with dithered exposures. The median
surface brightness depth, estimated at 3σ for a 10"x10" region,
is 30.5±0.2mag/arcsec2 in the g-band and 29.7±0.2mag/arcsec2
in the r-band. This depth is approximately two magnitudes deeper than
DES data and is comparable to the 10-year LSST co-added dataset.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 118 171 Abell 194 LSBS catalog (table B1)
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Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 26 A26 --- Name Name of the LSBG based on the
coordinated of the sources
(JHH:MM:SS.sss-DD:MM:SS.sss)
28- 35 F8.5 deg RAdeg Right Ascension (J2000) from galfit (RA)
37- 44 F8.5 deg DEdeg Declination (J2000) from galfit (DEC)
46- 49 F4.2 --- n Sersic index (n)
51- 54 F4.2 --- b/a Axis ratio (q)
56- 60 F5.1 deg PA [] Position angle (PA)
62- 64 F3.1 [Msun/kpc2] log(Sigma*) Stellar mass surface density in log scale
66- 68 F3.1 [Msun] log(M*) Stellar mass in log scale
70- 72 F3.1 arcsec reff-g Half-light radius, g-band
74- 77 F4.1 mag Eg Extinction corrected g-band magnitude
79- 82 F4.1 mag/arcsec2 mumean-g g-band mean surface brightness
84- 86 F3.1 arcsec reff-r Half-light radius, r-band
88- 91 F4.1 mag Er Extinction corrected r-band magnitude
93- 96 F4.1 mag/arcsec2 mumean-r r-band mean surface brightness
98 A1 --- l_NUV Limit flag on NUV
99-102 F4.1 mag NUV Extinction corrected NUV magnitude
104-106 F3.1 mag e_NUV ? NUV magnitude error
108 A1 --- l_FUV Limit flag on FUV
109-112 F4.1 mag FUV Extinction corrected FUV magnitude
114-116 F3.1 mag e_FUV ? FUV magnitude error
118 I1 --- DES [0/1] If it has been reported in DES
(0 for no and 1 for yes)
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Acknowledgements:
Hareesh Thuruthipilly, hareesh.thuruthipilly(at)ncbj.gov.pl
(End) Patricia Vannier [CDS] 19-Feb-2025