The first galaxies could be surprisingly large and complex

Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) — an international observatory co-operated by the National Radio Astronomy Observatory (NRAO) of the U.S. National Science Foundation — 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, Calif., 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 Virgo cluster. It was discovered hidden behind the galaxy cluster Abell 1689 in 2007 and confirmed in 2015 through gravitational lensing, which magnified the young galaxy’s brightness by more than 9x. Since then, scientists have continued to study the galaxy as a possible analogue of the evolution of other “normal” galaxies. This label – normal – is an important distinction that helped researchers divide the behaviors and characteristics of A1689-zD1 into two categories: typical and unusual, with unusual characteristics mimicking those of newer, more massive galaxies.

“A1689-zD1 is located at the very beginning of the Universe – just 700 million years after the Big Bang. This is the era when galaxies were just beginning to form,” said undergraduate student Hollis Akins. graduate in astronomy at Grinnell College and author research director. “What we see in these new observations is evidence of processes that may contribute to the evolution of what we call normal galaxies as opposed to massive galaxies. More importantly, these processes are ones that we did not previously think 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 could be evidence of continued star formation in the same region or the result of structural disturbances, such as mergers or outflows, 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 likely much larger than previously thought.It’s also possible that this halo is a remnant of earlier galactic activity, such as mergers that exerted complex gravitational forces on the galaxy leading to the ejection of a large amount of neutral gas at these great distances. The galaxy was likely active and dynamic, and we learn that this may be a common, though previously unobserved, theme in the formation of early galaxies.”

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

Led by Akins, the team also observed outflows of hot, ionized gases – usually caused by violent galactic activity like supernovae – pushing outward from the center of the galaxy. It is possible, given their potentially explosive nature, that the flows 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 at the center of galaxies – which have strong magnetic effects that can ejecting materials in powerful For this reason, there is a strong possibility that the warm flows have something to do with the presence of the cold carbon halo, “said Akins. “And this again underlines the importance of nature multiphase, or hot to cold, of the outgoing gas.”

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 high redshift galaxy in 2015, making it the dusty galaxy the farthest known. “We’ve seen this type of extended gas halo emission from galaxies that formed later in the Universe, but seeing it in such an old galaxy means this type of behavior is universal even in smaller galaxies. which formed most of the stars in the Universe. Understanding how these processes occurred in such a young galaxy is essential to understanding how star formation occurs in the early Universe.”

Kirsten Knudsen, professor of astrophysics in the Department of Space, Earth and Environment at Chalmers University of Technology, and co-author of the research, found evidence of the A1689 dust continuum -zD1 in 2017. Knudsen emphasized the serendipitous role of extreme lensing gravity in making possible every new discovery in research. “Because A1689-zD1 is magnified more than nine times, we can see critical details that are otherwise difficult to observe in ordinary observations of galaxies this far away. Ultimately, what we see here is that the early galaxies in the Universe are very complex, and this galaxy will continue to present new challenges and research results 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 nevertheless really interesting and exciting!”

Infrared spectroscopy and observations of 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, providing a deeper and more comprehensive multi-wavelength look at the young galaxy.