Further evidence for a population of dark-matter-deficient dwarf galaxies


In the standard cosmological model, dark matter drives the structure formation of galaxies and constructs potential wells within which galaxies may form. The baryon fraction in dark halos can reach the Universal value (15.7%) in massive clusters and decreases rapidly as the mass of the system decreases1,2. The formation of dwarf galaxies is sensitive both to baryonic processes and the properties of dark matter owing to the shallow potential wells in which they form. In dwarf galaxies in the Local Group, dark matter dominates the mass content even within their optical-light half-radii (re ≈ 1 kpc)3,4. However, recently it has been argued that not all dwarf galaxies are dominated by dark matter5,6,7. Here we report 19 dwarf galaxies that could consist mainly of baryons up to radii well beyond re, at which point they are expected to be dominated by dark matter. Of these, 14 are isolated dwarf galaxies, free from the influence of nearby bright galaxies and high-density environments. This result provides observational evidence that could challenge the formation theory of low-mass galaxies within the framework of standard cosmology. Further observations, in particular deep imaging and spatially resolved kinematics, are needed to constrain the baryon fraction better in such galaxies.

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Fig. 1: Image and spectra of two galaxy examples.
Fig. 2: Comparison of baryonic mass and total mass enclosed within rH i.
Fig. 3: Galaxy properties.
Fig. 4: Halo mass and distance to the nearest clusters/groups.

Data availability

The ALFALFA data are available in The Arecibo Legacy Fast ALFA Survey and the SDSS data are available at the Sloan Digital Sky Survey (http://egg.astro.cornell.edu/alfalfa/data/index.php, https://www.sdss.org/). The other data that support the results of this study are available from the corresponding author upon reasonable request.

Code availability

We use standard data reduction tools in the IDL and Python environments, and the publicly available code SExtractor (https://www.astromatic.net/software/sextractor) for this study.


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This work is supported by the National Key R&D Program of China (grant number 2018YFA0404503, 2016YFA0400703 and 2016YFA0400702), the National Natural Science Foundation of China (grant numbers 11573033, 11622325, 11133003, 11425312, 11773001, 11721303, 11733006 and 11703036) and the National Natural Science Foundation of China (grant numbers 11573033, 11622325, 11133003, 11425312, 11773001, 11721303, 11733006, 11703036 and U1931110). Q.G. and L.G. acknowledge support from Royal Society Newton Advanced Fellowships. Z.Z. acknowledges the support by the Open Project Program of the Key Laboratory of FAST, Chinese Academy of Sciences.

Author information




Q.G. led and played a part in all aspects of the analysis, and wrote the manuscript. H.H. compiled the data and carried out most of the data reduction and analysis. Z.Z. measured the optical photometry of the low-surface-brightness galaxy. SH.L. carried out most of the analysis related to various mass determinations. All authors contributed to the analysis and to the writing of the manuscript.

Corresponding author

Correspondence to Qi Guo.

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Extended data

Extended Data Fig. 1 Comparison of the galaxy properties between different methods for dwarf galaxies in LITTLE THINGS.

a, Comparison of the rH i using our method with that obtained using tilted-ring method by LITTLE THINGS team. b, Comparison of the VH i using our method with that obtained using tilted-ring method by LITTLE THINGS team. c, Comparison of the dynamical mass estimated using our method with those derived using the tilted-ring method. Black and grey dots are measurements based on w20 and w50, respectively.

Extended Data 2 Distribution of the Mdyn-to-Mbary ratio with different misalignments between optical image and H i velocity field.

a, The distribution of the misalignment between optical image and H i velocity field for dwarf galaxies in LITTLE THINGS(red)/Illustris(cyan). b,c, Distribution of the Mdyn/Mbary ratio for our parent sample after applying the same distribution of misalignment between optical image and H i velocity field from the LITTLE THINGS/Illustris in the left panel. Grey histogram is based on 10,000 random realizations and black curve is the Gaussian fit. Samples classified as BDDGs are highlighted with blue histogram.

Extended Data 3 Comparison of rH i and re between the parent sample and the BDDGs.

a, rH i and re relation of the parent sample (black dots) and the BDDGs (blue dots). b, The distribution of rH i, grey histogram and blue histogram represent the parent sample and BDDGs respectively. c, The distribution of re, grey histogram and blue histogram represent parent sample and BDDGs respectively.

Extended Data Fig. 4

BDDGs data. Column 1 shows the ALFALFA galaxy ID; columns 2 and 3 show equatorial coordinates; column 4 shows the distance judged by ALFALFA group; column 5 shows the heliocentric velocity; column 6 shows the velocity width for 20% of the peak flux; column 7 shows the error of w20; columns 8 and 9 show the g-band and r-band magnitudes, respectively; column 10 shows the effective radius in the r-band; column 11 shows the neutral hydrogen mass; column 12 shows the stellar mass; column 13 shows the dynamical mass within rH i; column 14 shows the virial mass; column15 shows the r-band minor-to-major axis ratio; and column 16 shows the distance to the nearest group over virial radius.*In the literature AGC 6980 was defined as Abell 1367’s member (Leo cluster: \({\mathrm{c}}z = 6459\), RA = 176.15083, Dec. = 19.77194)55. The projected distance between the AGC 6980 and Abell 1367 is about 8 Mpc, well beyond 3Rvir of the Abell 1367. The minimum projected distance of the BDDG to its surrounding clusters with relatively small difference in redshifts (czBDDG – czcluster < 10 × Rcluster;vir) is <3 × Rvir.

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Guo, Q., Hu, H., Zheng, Z. et al. Further evidence for a population of dark-matter-deficient dwarf galaxies. Nat Astron 4, 246–251 (2020). https://doi.org/10.1038/s41550-019-0930-9

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