The first galaxies could be surprisingly large and complex

Researchers using the Atacama Large Millimeter / Submillimeter Array (ALMA) – an international observatory collaborating with the National Radio Astronomy Observatory (NRAO) of the United States National Science Foundation – have observed a significant amount of cold, neutral gas in the outer regions of the young galaxy A1689-zD1, as well as hot gas outflows from the center of the galaxy. These findings may shed light on a critical stage in galactic evolution for early galaxies, where young galaxies begin the transformation to increasingly resemble their later, more structured cousins. The observations were presented today at a press conference at the 240th meeting of the American Astronomical Society (AAS) in Pasadena, California, and will be published in an upcoming issue of The Astrophysical Journal (ApJ).

A1689-zD1 – a young, active, star-forming galaxy slightly less luminous and less massive than the Milky Way – is located about 13 billion light-years from Earth in the constellation Jomfruhoben. It was discovered hidden behind the galaxy cluster Abell 1689 in 2007 and confirmed in 2015 through gravitational lenses, which magnified the young galaxy’s brightness by more than 9x. Since then, scientists have continued to study the galaxy as a possible analogue to the evolution of other “normal” galaxies. This label – normal – is an important distinction that helped scientists divide the behavior and characteristics of A1689-zD1 into two categories: typical and unusual, with unusual properties that mimic those of newer, more massive galaxies.

“A1689-zD1 is located at the beginning of the universe – only 700 million years after the Big Bang. This is the era when galaxies had just begun to form,” said Hollis Akins, a bachelor’s student in astronomy at Grinnell College and lead author of the research. . “What we see in these new observations is evidence of processes that can contribute to the evolution of what we call normal galaxies as opposed to massive galaxies. More importantly, these processes are the ones we did not previously believe. was applied to these normal galaxies. ”

One such unusual process is the galaxy’s production and distribution of star – forming fuel and potentially a large amount of it. The team used ALMA’s highly sensitive Band 6 receiver to focus on a halo of carbon dioxide that extends far beyond the center of the young galaxy. This may be evidence of continued star formation in the same region or the result of structural disturbances, such as fusions or exits, in the early stages of galaxy formation.

According to Akins, this is unusual for early galaxies. “The carbon dioxide we have observed in this galaxy is generally found in the same regions as neutral hydrogen gas, which is also where new stars tend to form. If this is the case with A1689-zD1, the galaxy is probably much larger It is also possible that this halo is a remnant of previous galactic activity, such as fusions that exerted complex gravitational forces on the galaxy, leading to the ejection of a large amount of neutral gas at such great distances. The galaxy was probably active and dynamic, and we learn that this may be a common, but previously unobserved, theme in the formation of early galaxies. “

More than rarely, the discovery may have important implications for the study of galactic evolution, especially when radio observations reveal details that are invisible to optical wavelengths. Seiji Fujimoto, postdoctoral fellow at the Niels Bohr Institute’s Cosmic Dawn Center and co-author of the research, said: “The carbon dioxide emission in the A1689-zD1 is much more extensive than what has been observed with the Hubble Space Telescope, first galaxies are not as small as they appear.If the first galaxies are in fact larger than we previously thought, it would have a major impact on the theory of galaxy formation and evolution in the early universe.

Led by Akins, the team also observed outflows of hot, ionized gases – usually caused by violent galactic activity such as supernovae – pushing out of the galaxy’s center. It is possible, due to their potentially explosive nature, that the currents have something to do with the carbon halo. “Outflows occur as a result of violent activity, such as the explosion of supernovae – which propel nearby gaseous matter out of the galaxy – or black holes in the center of galaxies – which have strong magnetic effects that can push materials into powerful for this reason. , there is a strong possibility that the hot currents have something to do with the presence of the cold carbon halo, “said Akins.” And this again underlines the importance of the outgoing gas multiphase or heat to cold nature. »

Darach Watson, associate professor at the Cosmic Dawn Center at the Niels Bohr Institute and co-author of the new research, confirmed that A1689-zD1 was a tall redshift galaxy in 2015, making it the dustiest galaxy known for a long time. “We have seen this type of extended gashalo emission from galaxies formed later in the universe, but seeing it in such an ancient galaxy means that this type of behavior is universal even in smaller galaxies, which formed most of the stars in the universe. Understanding how these processes took place in such a young galaxy is crucial to understanding how star formation occurs in the early universe. “

Kirsten Knudsen, professor of astrophysics at the Department of Space, Earth and Environment at Chalmers University of Technology, and co-author of the research, found evidence for A1689 dust continuum -zD1 in 2017. Knudsen emphasized the serendipitic role of extreme lens gravity to enable any new discovery in research . “Because the A1689-zD1 has been magnified more than nine times, we can see critical details that are otherwise difficult to observe in ordinary observations of galaxies so far away. Ultimately, what we see here is that the early galaxies of the universe were very complex, and this galaxy will continue to present new challenges and research findings for some time to come. »

Dr. Joe Pesce, NSF Program Manager for ALMA, added: “This fascinating research from ALMA adds to a growing body of evidence indicating that things are not quite as we expected in the primitive universe, but they are nonetheless really interesting and exciting! “

Infrared spectroscopy and observations of the A1689-zD1 are scheduled for January 2023 using the NIRSpec Integral Field Unit (IFU) and NIRCam on the James Webb Space Telescope. The new observations will complement previous HST and ALMA data and provide a deeper and more comprehensive look at the multi-wavelength galaxy.

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