Chinese astronomers discover an isolated dark dwarf galaxy

Morphology of dark galaxy FAST J0139+4328. HI column-density map from the FAST observation shown in white contours overlaid on the Pan-STARRS1 g-band image in colorscale. Credit: Xu et al, 2023

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), Chinese astronomers have detected a new galaxy, which received designation FAST J0139+4328. The newfound galaxy is isolated, has a relatively low stellar mass, and is dominated by dark matter. The discovery was detailed in a paper published February 6 on the arXiv pre-print server.

China’s FAST is the world’s largest single-dish radio telescope. Its sensitivity and excellent survey speed allows astronomers to study compact objects, gaseous galaxies, and the interstellar medium. The potential discoveries of FAST include thousands of new pulsars, hundreds of thousands of new neutral atomic hydrogen (HI) galaxies, or dark galaxies that make up part of the so-called missing baryons.

Now, a team of astronomers led by Jin-Long Xu of the Chinese Academy of Sciences in Beijing, reports the finding of one new dark galaxy using FAST. The discovery is a result of analyzing the data from FAST’s HI survey and also from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS).

“A major scientific objective for this survey is to search for dark and weak galaxies taking advantage of high sensitivity of FAST and with a relatively high velocity resolution. In this Letter, based on the HI survey using FAST, we have discovered an isolated dark dwarf galaxy in the nearby universe,” the researchers explained.

First of all, the team detected some new neutral atomic hydrogen clouds in the local universe based on the new FAST extragalactic HI survey data. Among the detected clouds, they identified an isolated cloud, named FAST J0139+4328 according to its coordinates, which has no optical counterpart.

Further examination of FAST J0139+4328 found that a typical disk galaxy, however with an extremely low absolute magnitude (upper limit absolute B-band magnitude of -10.0 mag) and a stellar mass below 690,000 solar masses. The dynamical and baryonic masses of FAST J0139+4328 were calculated to be about 5.1 and 0.11 billion solar masses, respectively, while the neutral atomic hydrogen mass of this galaxy was found to be at a level of some 83 million solar masses.

The astronomers underlined that the dynamical mass to total baryonic mass ratio for FAST J0139+4328 is about 47± 27, which suggests that in this galaxy dark matter dominates over baryons. All in all, the results indicate that FAST J0139+4328 is an isolated gas-rich and dark dwarf galaxy located some 94 million light years away.

The authors of the paper noted that their discovery marks the first time when a gas-rich isolated dark galaxy has been detected in the nearby universe. They added that FAST J0139+4328 appears to have a rotating disk of gas but is starless. This, together with the fact that dark matter dominates in FAST J0139+4328, may suggest that this dark galaxy is in the earliest stage of the galaxy formation.

More information:
Jin-Long Xu et al, Discovery of an isolated dark dwarf galaxy in the nearby universe, arXiv (2023). DOI: 10.48550/arxiv.2302.02646

Journal information:

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Chinese astronomers discover an isolated dark dwarf galaxy (2023, February 14)
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