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.

• The paper reports the discovery of FAST J0139+4328, an isolated dark dwarf galaxy identified using the FAST telescope, bridging gaps between theoretical predictions and observations.
• The study employs sensitive radio observations combined with Pan-STARRS1 data to reveal the galaxy's double-peak signature, disk rotation, and extreme dark matter dominance.
• The findings address the missing satellite problem in ΛCDM cosmology and encourage further research on dark matter halos in starless or ultra-faint galaxies.

Discovery of an Isolated Dark Dwarf Galaxy in the Nearby Universe

In recent astrophysical studies, researchers have increasingly focused on examining the structure and distribution of dwarf galaxies to address discrepancies in predictions made by the Λ cold dark matter (ΛCDM) model. The paper "Discovery of an isolated dark dwarf galaxy in the nearby universe" presents a significant advancement in the study of such galaxies. Using highly sensitive observational techniques, the authors report the identification of FAST J0139+4328, an isolated dark dwarf galaxy, potentially bridging the gap between theory and observation.

Methodological Framework and Findings

The team employed the Five-hundred-meter Aperture Spherical radio Telescope (FAST), leveraging its unparalleled sensitivity to survey portions of the sky devoid of prominent optical signals. The process involved an integration of data collected via the Pan-STARRS1 optical images, which was instrumental in confirming the lack of an optical counterpart for the detected radio emission. Consequently, FAST J0139+4328 was discerned as an invisible disk galaxy with notable characteristics, distinguishable by its double-peak signature and disk-like rotation evidenced in the velocity-position diagram.

Further investigation revealed that FAST J0139+4328 possesses an exceptionally low absolute magnitude ($M_{\rm B} > -10.0$) and a diminutive stellar mass (less than $6.9 \times 10^5 M_{\odot}$). Its dynamic mass, elaborated through calculated rotational velocities and velocity dispersion, was determined to be $(5.1 \pm 2.8) \times 10^9 M_{\odot}$, resulting in a dynamical mass to baryonic mass ratio of 47 ± 27, emphasizing the dominance of dark matter within the galaxy. Notably, this makes FAST J0139+4328 an exciting candidate for researchers focusing on dark matter halos and their properties.

Implications for Astrophysics and Cosmology

This discovery is significant in several contexts. Firstly, FAST J0139+4328 provides a rare look at an isolated dark galaxy, devoid of interactions with nearby larger galaxies that typically complicate theoretical modeling. Its presence supports the theoretical prediction that isolated dark matter halos might exist in abundance and possess gas that fails to condense into stars, offering insights into the galaxy formation process at early cosmic times.

Second, the study contributes valuable empirical data towards the solution of the "missing satellite problem" in ΛCDM cosmology, where the number of observed dwarf galaxies falls short of model predictions. The identification of such starless or ultra-faint galaxies brings observational evidence closer to theoretical forecasts. Such galaxies may have been overlooked by traditional optical surveys due to their inherent lack of luminosity, caused by minimal star formation relative to their gas content.

Future Research Directions

Looking forward, this discovery sets the stage for multiple avenues of research in galactic formation and dark matter studies. Higher resolution observations and further analysis of similar detections could unveil more dark dwarf galaxies, enriching models of galaxy formation. These could also aid in refining the baryonic Tully-Fisher relation for gas-dominated galaxies with minimal luminosity, adding depth to our understanding of their dynamics and structure.

In summary, this research underscores the necessity and potential of utilizing cutting-edge technology like FAST to uncover celestial bodies previously hidden from view. It highlights the importance of integrating multi-wavelength datasets to assess different components of the universe and invites further theoretical explorations into the dark matter halos that characterize the faintest corners of our cosmic neighborhood.