REBELS-25 is a dynamic cold disk galaxy, according to observations

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HST WFC3 F160W image of REBELS-25 from the COSMOS-DASH mosaic showing the [CII] emission and dust continuum shown by the turquoise and orange contours, respectively. Credit: Rowland et al., 2024.

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HST WFC3 F160W image of REBELS-25 from the COSMOS-DASH mosaic showing the [CII] emission and dust continuum shown by the turquoise and orange contours, respectively. Credit: Rowland et al., 2024.

An international team of astronomers has spotted a massive, high-redshift star-forming galaxy known as REBELS-25. They discovered that REBELS-25 is a dynamic cold disk galaxy. This finding was presented in a research paper published on the pre-print server on May 9 arXiv.

With a redshift of 7.31, which corresponds to a luminosity distance of about 236 billion light-years, REBELS-25 is an infrared luminous galaxy. It has a stellar mass of about 8 billion solar masses and its star formation rate is estimated at a level of 199 solar masses per year.

Recently, a group of astronomers led by Lucie E. Rowland of Leiden University in the Netherlands decided to conduct high-resolution REBELS-25 dust continuum observations to shed more light on its properties. For this purpose they used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

“In this paper, we have presented the high-resolution (∼710 pc) follow-up ALMA [CII] and dust (∼150𝜇m) continuum observations from REBELS-25; a massive star-forming galaxy at 𝑧=7.31, originally intended as part of the ALMA Reionization Era Bright Emission Line Survey (REBELS) large program (LP),” the researchers wrote.

The observations showed that REBELS-25 has a relatively low velocity dispersion of about 33 km/s and a high ratio of ordered to random motions – at a level of 11.0. These results indicate that REBELS-25 is a dynamic cold disk galaxy.

However, although REBELS-25 appears to be dynamically cold, astronomers have observed some evidence of non-circular motion. These movements can result from inflow or outflow, a small merging component, but also from a central rod or spiral arms.

The observations also revealed that REBELS-25 has a total dynamic mass of approximately 120 billion solar masses. Based on this, the researchers estimate that the gas mass of the galaxy is about 110 billion solar masses, but this result is highly uncertain due to the obscuring by dust and requires further research.

The paper’s authors underlined that their discovery makes REBELS-25 one of the most distant, robustly confirmed cold disk galaxies observed to date. They added that finding such a very distant and highly dynamic cold disk galaxy is a challenge to current theoretical predictions and simulations. It also suggests that such galaxies are more common in the high-redshift universe than previously thought.

‘We therefore expect that future high-resolution studies of cold gas kinematics at high z will reveal even more cold, massive disks. In particular, continued ALMA observations of other REBELS galaxies will enable robust kinematic modeling of additional rotating disk candidates at 𝑧∼. 6−8,” the scientists conclude.

More information:
Lucie E. Rowland et al, REBELS-25: Discovery of a dynamic cold disk galaxy at z = 7.31, arXiv (2024). DOI: 10.48550/arxiv.2405.06025

Magazine information:
arXiv

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