Discovery of an isolated dark dwarf galaxy in the nearby universe

Abstract

Based on a new HI survey using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), combined with the Pan-STARRS1 images, we identified an isolated HI cloud without any optical counterpart, named FAST J0139+4328. The newly discovered HI cloud appears to be a typical disk galaxy since it has a double-peak shape in the global HI profile and an S-like rotation structure in the velocity-position diagram. Moreover, this disk galaxy has an extremely low absolute magnitude (M_B>-10.0 mag) and stellar mass (<6.9*10^5 Msun). Furthermore, we obtained that the HI mass of this galaxy is 8.3*10^7 Msun, and the dynamical mass to total baryonic mass ratio is 47+-27, implying that dark matter dominates over baryons in FAST J0139+4328. These findings provide observational evidence that FAST J0139+4328 is an isolated dark dwarf galaxy with a redshift of z=0.0083. This is the first time that an isolated dark galaxy has been detected in the nearby universe.

13 pages, 3 figures, Accepted for publication in the ApJ Letters

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• The FAST all sky HI survey (FASHI): The first release of catalog
• EDGE: The emergence of dwarf galaxy scaling relations from cosmological radiation-hydrodynamics simulations
• MHONGOOSE discovery of a gas-rich low-surface brightness galaxy in the Dorado Group
• Not so-dark: High resolution HI imaging of J0139+4328 and identification of an optical counterpart
• Unveiling the nature and fate of the almost-dark cloud AGC 226178 through HI mapping
• HI-bearing dark galaxies predictions from constrained Local Group simulations: how many and where to find them
• HI Content of Group Galaxies from the FAST All Sky HI Survey