Discovery of an Isolated Dark Dwarf Galaxy in the Nearby Universe

Abstract

Based on a new H i survey using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), combined with the Pan-STARRS1 images, we identified an isolated H i cloud without any optical counterpart, named FAST J0139+4328. The newly discovered H i cloud appears to be a typical disk galaxy since it has a double-peak shape in the global H i 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 ×105 M ⊙). Furthermore, we obtained that the H i mass of this galaxy is (8.3 ± 1.7) ×107 M ⊙, 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.

Dark Galaxies, Sun-Earth-Moon Interaction, Tunguska Event—Explained by WUM

“…Their findings provide observational evidence that this galaxy 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 [6].…”

The FAST all sky H i survey (FASHI): The first release of catalog

“…In several case studies (e.g., Liu et al, 2023;Yu et al, 2023a,b;Zhou et al, 2023;Zhu et al, 2021), FASHI has detected intergalactic and surrounding diffuse gas that has not been detected by other telescopes. The work of Xu et al (2023b) shows that FASHI can potentially discover more candidates of "dark galaxies" that do not form any star due to low-density gas and, therefore, reveal the mystery of dark halo substructure.…”

“…Using the probability method above, we will always find an SDSS target as the most likely counterpart to the H I target. However, for the optically faint galaxies (Gray et al, 2023;Leisman et al, 2017;Xu et al, 2023b), the SDSS image is not deep enough to detect the targets, or the low surface brightness galaxies are not detected by the SDSS pipeline. On the 4) https://www.legacysurvey.org/sga/sga2020/ 5) http://mastweb.stsci.edu/mcasjobs/ 219511-16 other hand, for a H I target with SDSS coverage but no SDSS spec-z counterparts, the optical counterpart would be fainter than m r ∼ 17.7.…”

Understanding the Formation and Evolution of Dark Galaxies in a Simulated Universe

“…However, if they contain baryonic content like a gas reservoir, they could be detectable through 21 cm radiation from neutral hydrogen (H I) gas, which would make them appear as H I sources without an optical counterpart. Several candidates for dark galaxies have been proposed, including VIRGOHI21 (Minchin et al 2005), Dragonfly 44 (van Dokkum et al 2016), AGESVC1 282 (Bílek et al 2020), AGC 229101 (Leisman et al 2021), and FAST J0139+4328 (Xu et al 2023). However, their existence remains under debate because other possible explanations, not of cosmological origin, have also been suggested.…”