The first galaxies could be bigger and more complex than we thought


The artist’s impression shows the previously unknown complexity of the young galaxy, A1689-zD1.

Scientists used ALMA (Atacama Large Millimeter/submillimeter Array) to observe significant amounts of cold, neutral gas in the outer regions of the young galaxy A1689-zD1, as well as streams of hot gas from the center of the galaxy.

These findings could shed light on a critical phase of galactic evolution for early galaxies, where young galaxies begin the transformation to increasingly resemble their more recent, more structured cousins.

The sightings were present at a press conference at the 240th meeting of the American Astronomical Society in Pasadena, Calif., and will be published in an upcoming issue of The Astrophysical Journal.

A1689-zD1 – a young active galaxy in star formation slightly less luminous and less massive than the Milky Way – it is located about 13 billion light-years from Earth in the direction of the constellation of Virgo.

Was discovered hidden behind the galactic cluster Abell 1689 in 2007 and confirmed in 2015 thanks to the gravitational lens, which magnified more than 9 times the luminosity of the young galaxy.

Since then, scientists have continued to study the galaxy as a possible analogue of the evolution of other “normal” galaxies.

This label – Ordinary — is an important distinction that helped researchers divide the behaviors and characteristics of A1689-zD1 into two groups: typical and unusual, with the unusual characteristics mimicking those of newer, more massive galaxies.

A1689-zD1 is located in the Prime Universe – barely 700 million years after the Big Bang. This is when galaxies were just beginning to form,” he said. Hollis Akinsundergraduate student of astronomy at Grinnell College and lead author of the survey.

“What we see in these observations is evidence of processes that may contribute to the evolution of what we call normal galaxies, unlike massive galaxies. More importantly, these processes are processes that we did not previously think apply to these normal galaxies.

One of these unusual processes is the production and distribution in the galaxy of fuel for star formationpotentially in large quantities.

The team used ALMA’s highly sensitive Band 6 receiver to observe 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 for A1689-zD1 , the galaxy is likely much larger than previously thought.

“It is also possible that this halo is a remnant of galactic activity earlier, like mergers that exerted complex gravitational forces on the galaxy, leading to the ejection of a lot of neutral gas at these great distances,” adds the astronomer.

“In either case, the early evolution of this galaxy was probably active and dynamic and we learn that this can be a common themealthough not observed before, in the formation of the first galaxies,” concludes Akins.

More than unusual, the discovery could have important implications for the study of galactic evolution, especially as radio observations unfold. invisible details at optical wavelengths.

Seiji Fujimotopostdoctoral researcher at the Cosmic Dawn Center of the Niels Bohr Institute, co-author of the research, said: “The emission of carbon dioxide in A1689-zD1 is much larger than that 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 will have great impact on theory of the formation and evolution of galaxies in the early Universe,” adds Fujimoto.

Led by Akins, the team also observed outflows of hot, ionized gases — often triggered by violent galactic activity like supernovae — pushing outward from the center of the galaxy. Given its potentially explosive nature, fluxes may have something to do with carbon halo.

“Flows happen like result of violent activitylike supernova explosions – which blast nearby gaseous matter out of the galaxy — or black holes at the center of galaxies — which have strong magnetic effects that can eject matter in powerful jets,” Akins said.

“For this reason, there is a strong possibility that the hot fluxes have something to do with the presence of the cold carbon halo. And that rfurther emphasizes the importance multiphase, or hot to cold, nature of the gas stream,” he added.

Darach Watson, associate professor at the Niels Bohr Institute’s Cosmic Dawn Center and co-author of the new survey, confirmed that A1689-zD1 was a high redshift galaxy in 2015, the most distant dusty galaxy known.

“We’ve seen this type of prominent gas halo emission from galaxies that formed later in the Universe, but seeing it in such an old galaxy means that this behavior is universal even in the smallest galaxies that formed most of the stars in the early Universe,” Watson said.

“Understanding how these processes occurred in such a young galaxy is essential for understand how stars form in the primordial Universe,” added the astronomer.

Kirsten Knudsenprofessor 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 dust continuum of A1689-zD1 in 2017 Knudsen pointed to the serendipitous role of extreme gravitational lensing in making every possible find in the survey.

“Because A1689-zD1 is magnified more than nine times, we can see critical details that are otherwise difficult to observe in routine observations of galaxies so far away. At the end of the day, we see here that the first galaxies of the Universe are very complex and this galaxy will continue to present new challenges and research results for some time to come,” said the researcher.

Doctor. Joe Pesce, ALMA program manager at the NSF, added: “This fascinating ALMA investigation adds to a growing body of findings that indicate things are not quite as we expected in the early Universe. , but they are nevertheless interesting and exciting!”

Spectroscopic and infrared observations of A1689-zD1 are planned for January 2023, using the NIRSpec IFU (Integral Field Unit) and NIRCam instruments of the James Webb Space Telescope.


The new observations will complement previous data from Hubble and ALMA, providing a deeper and more comprehensive multi-wavelength look at the young galaxy.

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