J/ApJS/279/38 Dark galaxy candidates from ALFALFA & DESI images (Kwon+, 2025)
Searching for dark galaxies with HI detection from the Arecibo Legacy Fast ALFA
(ALFALFA) survey.
Kwon M., Hwang Ho S., Kent B.R., Yoon I., Lee G., Yoon H.
<Astrophys. J. Suppl. Ser., 279, 38 (2025)>
=2025ApJS..279...38K 2025ApJS..279...38K
ADC_Keywords: Galaxies; H I data; Radial velocities; Optical; Surveys
Keywords: H I line emission ; Dark matter ; Dwarf galaxies ; Galaxy formation ;
Galaxy evolution
Abstract:
We present a catalog of 142 dark galaxy candidates in a region covered
by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We start with
344 ALFALFA HI sources without optical counterparts and remove those
that do not seem to have a dark galaxy origin. To do that, we first
eliminate 83 sources that are known HI clouds probably formed from
tidal interactions between galaxies and 13 sources that have optical
counterparts. We then remove 56 sources located near other HI sources,
which are likely to be HI clouds. We further exclude 10 sources that
have nearby HI sources within the ALFALFA beam and 40 sources
potentially associated with nearby galaxies. We perform visual
inspection of optical images from the DESI Legacy Imaging Survey with
an r-band surface brightness limit of ∼28.5mag/arcsec2 as well as
near-ultraviolet images from GALEX to confirm the absence of stellar
emission. We additionally inspect infrared images from the Wide-field
Infrared Survey Explorer and AKARI for dust emission. As a result, we
identify 142 dark galaxy candidates and analyze their physical
properties by comparing them with luminous galaxies. We find that the
dark galaxy candidates generally have smaller dynamical masses, higher
HI-to-dynamical mass ratios, and are located in less dense regions
when compared to luminous galaxies, which is consistent with results
from cosmological simulations. This sample provides an important
testbed for studying the role of dark matter in galaxy formation and
evolution.
Description:
The Arecibo Legacy Fast ALFA (ALFALFA) survey mapped over ∼7000deg2 of
the high-Galactic-latitude sky to detect extragalactic HI sources,
exploiting the large collecting area of the Arecibo telescope.
The survey was conducted using the seven beam L-band (1.4GHz)
receiver, which covers 1335-1445MHz with 4096 equally spaced spectral
channels; this corresponds to a redshift range of
-2000<cz☉(km/s)<17912 with a spectral resolution of 5.1km/s at
1420.4MHz.
Haynes+ (2018, J/ApJ/861/49) presented 31502 extragalactic HI sources
from the ALFALFA survey. As this is a "untargeted" survey, they were
able to identify 344 intriguing sources that have no optical
counterparts among ∼25000 high-quality detections (i.e., SNR≳6.5,
HI_code=1 in their Table 2).
We utilized deep optical imaging to quantitatively determine the
probability that a HI source has an optical counterpart. To do that,
we use the optical images from Data Release 10 of the DESI Legacy
Imaging Survey. The survey consists of three projects including
DECaLs, BASS, and MzLS, and covers ∼14000deg2 of the northern sky in
three optical bands (g, r, z).
We also use data from the Galaxy Evolution Explorer (GALEX) in the
near-ultraviolet channel (2315Å), the Wide-field Infrared Survey
Explorer (WISE) in band 1 (3.4um) and 4 (22um), and from AKARI in band
S (90um) to identify potential ultraviolet/infrared emission from
stellar or dust components. We construct cutout images for each galaxy
to determine whether there is an optical counterpart, as shown in
Figure 2.
See Section 2.2.3.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 129 344 Dark galaxy candidates catalog
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See also:
VII/86 : Groups of Galaxies. I. Nearby Groups (Huchra+ 1982)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
V/154 : Sloan Digital Sky Surveys (SDSS), Release 16 (DR16) (Ahumada+, 2020)
J/AJ/138/338 : Arecibo Legacy Fast ALFA Survey. IX. (Stierwalt+, 2009)
J/MNRAS/415/1883 : AGES HI sources in NGC 7448 (Davies+, 2011)
J/AJ/142/170 : ALFALFA survey: α.40 HI source catalog (Haynes+, 2011)
J/A+A/584/A113 : Gas dynamics in tidal dwarf galaxies (Lelli+, 2015)
J/MNRAS/460/2143 : HI size-mass relation of galaxies (Wang+, 2016)
J/ApJ/861/49 : ALFALFA extragalactic HI source catalog (Haynes+, 2018)
J/AJ/157/194 : ALFALFA HI fluxes for extended sources (Hoffman+, 2019)
J/A+A/642/L10 : AGESVC1 282 deep optical image (Bilek+, 2020)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- AGC [102300/749170] Arecibo General Catalog (AGC)
entry
8- 15 A8 --- Name Common name of associated optical counterpart
17- 24 F8.4 deg RAdeg Right Ascension in decimal degrees (J2000)
26- 32 F7.4 deg DEdeg [-0.007/35.7] Declination (J2000)
34- 38 I5 km/s Vhel [136/17469] Heliocentric velocity of the HI
profile midpoint, cz☉
(from Haynes+ 2018, J/ApJ/861/49)
40- 44 F5.1 Mpc Dist [1/255] Distance, DHI
46- 48 F3.1 Mpc e_Dist [1.2/4.4] Uncertainty in Dist
50- 54 F5.1 km/s SNR [4.4/327] S/N
56- 58 I3 km/s W50 [12/407] Velocity width, measured at 50%
level of peak
60- 62 I3 km/s W20 [0/437] Velocity width, measured at 20% level
of peak
64- 68 F5.2 [Msun] logMHI [5.28/10.51] Logarithmic HI mass
70- 73 F4.2 [Msun] e_logMHI [0.05/1.2] Uncertainty in logMHI
75- 79 F5.2 [Msun] logMdyn [7/11.6] Logarithmic dynamical mass
81- 84 F4.2 [Msun] e_logMdyn [0.38/1.4] Uncertainty in logMdyn
86- 90 F5.3 --- Asym [0/0.61] HI line asymmetry
92- 97 F6.3 --- rho20 [-1/59.4] Local density (1)
99- 103 F5.3 --- LR [0/1] Likelihood ratio
105- 110 F6.3 Mpc dmin [0.002/20.9] Minimum projected distance to
other ALFALFA sources
112 I1 --- Q [0/6]? Quality code; see Table 2 (2)
114- 129 A16 --- Note Additional note(s) (3)
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Note (1): The local density derived from Equation (2); Section 2.3.2.
We normalize the local density to the mean density within the ALFALFA
survey volume.
Note (2): Quality code as follows:
0 = Final dark galaxy candidates (142 occurrences)
1 = H I clouds identified in the literature (83 occurrences)
2 = H I sources with optical counterparts identified in the literature
(13 occurrences)
3 = H I clouds excluded by the minimum projected distance criterion
(56 occurrences)
4 = H I sources with another HI source within the ALFALFA beam
(10 occurrences)
5 = H I sources with associated galaxies identified using
the NED and DESI catalog (16 occurrences)
6 = H I sources with potential optical counterparts identified
using the NED and DESI catalog (24 occurrences)
Note (3): For H I sources, such as potential optical counterparts,
related galaxies, or existence of foreground stars.
[C1995] = 1995AJ....109.2415C 1995AJ....109.2415C
[C2014] = 2014ApJ...787L...1C 2014ApJ...787L...1C
[C2015] = 2015AJ....149...72C 2015AJ....149...72C
[D2011] = 2011MNRAS.415.1883D 2011MNRAS.415.1883D (J/MNRAS/415/1883)
[D2024] = 2024ApJ...964...85D 2024ApJ...964...85D
[H2007] = 2007ApJ...665L..19H 2007ApJ...665L..19H
[J2015] = 2015ApJ...801...96J 2015ApJ...801...96J
[K2008] = 2008IAUS..244..362K 2008IAUS..244..362K
[K2014] = 2014MNRAS.443.3601L 2014MNRAS.443.3601L
[L2012] = 2012MNRAS.427.2314L 2012MNRAS.427.2314L
[L2016] = 2016MNRAS.463.1692L 2016MNRAS.463.1692L
[N1997] = 1997AJ....114...77N 1997AJ....114...77N
[S2009] = 2009AJ....138..338S 2009AJ....138..338S (J/AJ/138/338; in Simbad)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 24-Feb-2026