J/A+A/705/A78 Dwarf galaxies within the Kilo Degree Survey (Venhola+, 2026)
Dwarf galaxies within the Kilo Degree Survey.
Venhola A., Mueller O.
<Astron. Astrophys. 705, A78 (2026)>
=2026A&A...705A..78V 2026A&A...705A..78V (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, optical ; Photometry, ugriz
Keywords: galaxies: dwarf
Abstract:
Constraining the properties, spatial distribution, and luminosity
function of dwarf galaxies in different galactic environments is
crucial for understanding the dwarf galaxy formation and evolution.
Large surveys such as the Kilo Degree Survey (KiDS) provide useful
publicly available datasets that can be used to identify dwarf galaxy
candidates in a range of galactic neighborhoods. The resulting
catalogs are useful for constraining the abundance of dwarfs in
different environments and also provide useful galaxy samples for
future follow-up studies. Ultimately this analysis of low-mass
galaxies also provides constraints on our cosmological galaxy
formation models.
We generated a dwarf galaxy candidate catalog based on the KiDS
images. KiDS data covers a 1004 deg2 area in u', g', r', and
i' filters that is centered on two horizontal stripes at the equator
and in the southern hemisphere. In our catalog we provide the
locations, photometric properties, and visual classifications of dwarf
galaxy candidates within 60 Mpc in all different environments covered
by the KiDS. We also use the catalog to analyze the dwarf galaxy
numbers and distributions in groups as a function of groups' virial
mass.
We used Max-Tree Objects (MTO) to identify sources from the KiDS data.
We then selected objects based on their detection sizes and surface
brightness. We used automated photometric pipeline to run GALFIT on
the images in order to measure the structure, brightness, and color of
the objects. We then used size, surface brightness, and color cuts to
exclude the likely background galaxies and classify the likelihoods of
the remaining objects being dwarf galaxies based on their visual
appearance. We also probed the completeness limits and detection
biases of our detection procedure, by embedding simulated galaxies
into the KiDS images.
Our catalog contains galaxies that have Re larger than 3 arcsec and
reaches the 50% completeness limit at the r'-band mean effective
surface brightness of 26mag/arcsec2. Near the completeness limit
there is a slight selection bias toward detecting more round and
centrally peaked objects more effectively than the more elongated and
centrally flat. Altogether we identified 4x107 objects from the KiDs
data. After applying the size, color, and surface brightness cuts, we
were left with 6230 objects for which we performed photometry and
visual classifications. We ranked those objects into five classes
based on their likeliness of being a dwarf. We identified 763 galaxies
as clear dwarfs, 793 as likely dwarfs, and 933 as possible dwarfs. The
remaining objects are likely not dwarfs. Based on the distances of
groups that the dwarfs are likely to be associated with, the dwarfs
are expected to lie at distances of between 14Mpc-60Mpc. The majority
of dwarfs in the sample have magnitudes of between 14mag<mr<20mag,
effective radii of between 1arcsec<Re<30arcsec, and mean effective
surface brightnesses of between
21mag/arcsec2<µ{bar}r,e<25mag/arcsec2. We compare the
measured properties of the galaxies in our catalog with values from
the literature and find mostly good agreement between those, when
considering the differences in the data qualities. The only exceptions
are the effective radii, which are systematically smaller in our
catalog, due to the background subtraction method used in the KiDS
data reduction. We also identify the most likely associations with
groups and cluster for all the dwarfs in our catalog. Additionally we
compare the number of dwarfs and their distribution within the groups
with similar dwarfs found in the Illustris-TNG simulations. We find no
statistically significant tension between the dwarf numbers and
distributions between the observations and the simulations.
Our catalog contains locations, colors, structural parameters, and
likely group memberships for 2489 dwarf galaxy candidates. All the
measurements are publicly available. The catalog can be used to study
properties of dwarfs in a range of environments and it provides a good
dataset for follow-up studies.
Description:
Table A1 contains the positions, sizes and magnitudes of all
statistically significant objects from the Kilo Degree Survey data as
detected by MTO. The Table B1 contains the likely dwarf galaxy
candidates from that dataset and their photometric properties and
likely groups.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 39 65547041 All detections from KiDS
tableb1.dat 140 2489 Dwarf candidates
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg [0/360] Right Ascension J2000
11- 19 F9.5 deg DEdeg Declination J2000
21- 25 F5.2 mag rmag ? Detection magnitude in r' band
27- 33 F7.1 arcsec Re Detection effective radius
35- 39 F5.2 mag/arcsec2 mur ? Mean effective surface brightness in r-band
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- ID Identification number
6- 14 F9.5 deg RAdeg Right Ascension J2000
16- 24 F9.5 deg DEdeg Declination J2000
26- 30 F5.2 mag rmag Total r'-band magnitude from GALFIT
32- 35 F4.2 mag e_rmag Uncertainty of rmag
38- 42 F5.2 arcsec Re Effective radius from GALFIT
44- 48 F5.2 arcsec e_Re Uncertainty of Re
50- 53 F4.2 --- n Sersic index from GALFIT
55- 58 F4.2 --- e_n Uncertainty of n
60- 63 F4.2 --- b/a Axis-ratio from GALFIT
65- 68 F4.2 --- e_b/a Uncertainty of b/a
71- 75 F5.2 mag umagAp ?=-1 Aperture magnitude in u-band, aperr=Re
77- 81 F5.2 mag e_umagAp ?=-1 Uncertainty of amag_u
84- 88 F5.2 mag gmagAp ?=-1 Aperture magnitude in g-band, aperr=Re
90- 94 F5.2 mag e_gmagAp ?=-1 Uncertainty of amag_g
97-101 F5.2 mag rmagAp ?=-1 Aperture magnitude in r-band, aperr=Re
103-107 F5.2 mag e_rmagAp ?=-1 Uncertainty of amag_r
110-114 F5.2 mag imagAp ?=-1 Aperture magnitude in i-band, aperr=Re
116-120 F5.2 mag e_imagAp ?=-1 Uncertainty of amag_i
122-128 F7.3 --- RFF ?=-99 Residual flux fraction
129-137 A9 --- Group Name of the possible group
140 I1 --- MClass Morphological class
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Acknowledgements:
Aku Venhola, aku.venhola(at)oulu.fi
(End) Aku Venhola [Univ. Oulu], Patricia Vannier [CDS] 03-Dec-2025