HST WFC3 F160W Image of REBELS-25 from the COSMOS DASH mosaic with the [CII] Emission and dust continuum represented by the turquoise and orange contours, respectively. Image credit: Rowland et al., 2024.
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HST WFC3 F160W Image of REBELS-25 from the COSMOS-DASH mosaic with the [CII] Emission and dust continuum represented by the turquoise and orange contours, respectively. Image credit: Rowland et al., 2024.
An international team of astronomers has observed a massive, high-redshift star-forming galaxy called REBELS-25. They found that REBELS-25 is a dynamically cold disk galaxy. This result was presented in a research paper published on May 9 on the preprint server arXiv.
At 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 around 8 billion solar masses and its star formation rate is estimated at 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 and dust continuum observations of REBELS-25 to shed more light on its properties. For this purpose, they used the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.
βIn this article we presented the successor model ALMA with high resolution (approx. 710 percent). [CII] and dust (βΌ150πm) continuum observations from REBELS-25; a massive star-forming galaxy at π§=7.31 that was originally targeted as part of the large program (LP) ALMA Reionization Era Bright Emission Line Survey (REBELS),β the researchers wrote.
The observations revealed that REBELS-25 has a relatively low velocity dispersion of about 33 km/s and a high ratio of ordered to random motion – at a level of 11.0. These results suggest that REBELS-25 is a dynamically cold disk galaxy.
Although REBELS-25 appears to be dynamically cold, astronomers have observed some evidence of non-circular motion. These movements could be due to inflows or outflows, a minor merger component, and a central bar or spiral arms.
The observations also revealed that REBELS-25 has a total dynamic mass of about 120 billion solar masses. Based on this, the researchers estimated that the galaxy’s gas mass is about 110 billion solar masses. However, this result is extremely uncertain due to dust opacity and requires further investigation.
The paper’s authors emphasized that their discovery makes REBELS-25 one of the most distant, reliably confirmed cold disk galaxies observed to date. They added that the discovery of such a distant and very dynamically cold disk galaxy challenges current theoretical predictions and simulations. It also suggests that such galaxies may be more common in the high redshift Universe than previously thought.
βWe therefore expect that future high-resolution studies of cold gas kinematics at high Z will reveal even more cold, massive disks. In particular, ongoing ALMA observations of other REBELS galaxies will enable robust kinematic modeling of additional rotating disk candidates at π§βΌ.β 6β8,β the scientists conclude.
More information:
Lucie E. Rowland et al, REBELS-25: Discovery of a dynamically cold disk galaxy at z = 7.31, arXiv (2024). DOI: 10.48550/arxiv.2405.06025
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