A young but completely evolved galaxy, entirely self-built

Color image of the galaxy C1-23152 with red shift z = 3.352, when the universe was 1.8 billion years old. The image is the sum of three images at different wavelengths taken with the Hubble Space Telescope. C1-23152 appears a regular spheroid galaxy, its light profile corresponds to that of the elliptical galaxies typical of the local universe. Its stellar mass is about 200 billion stars like the sun and was formed in less than 500 million years. Credit: National Institute of Astrophysics

So young and already so evolved: thanks to the observations obtained at the Large Binocular Telescope, an international team of researchers coordinated by Paolo Saracco of the National Institute of Astrophysics (INAF, Italy) was able to reconstruct the wild evolutionary history of an extremely mass that existed 12 billion years ago, when the universe was only 1.8 billion years old, less than 13% of its current age. This galaxy, dubbed C1-23152, formed in just 500 million years, an incredibly short time to give rise to a mass of around 200 billion suns. To do so, it produced up to 450 stars per year, more than one per day, a star formation rate nearly 300 times higher than the current rate in the Milky Way. The information obtained from this study will be fundamental for the galaxy formation models for objects that are currently difficult to account for.

The most massive galaxies in the universe reach masses several hundred billion times that of the sun and, although numerically only one third of all galaxies, they contain more than 70% of the stars in the universe. For this reason, the speed with which these galaxies formed and the dynamics involved are among the most debated issues in modern astrophysics. The current model of galaxy formation, the so-called hierarchical model, predicts that smaller galaxies formed earlier, while more massive systems formed later, through the successive mergers of smaller pre-existing galaxies.

On the other hand, some of the properties of the most massive galaxies observed in the local universe, such as the age of their stellar populations, suggest instead that they were formed in primordial times. Unfortunately, the variety of evolutionary phenomena that galaxies can undergo during their life does not allow astronomers to define how they formed, leaving large margins of uncertainty. However, an answer to these questions may come from studying the properties of massive galaxies in the early universe, as close as possible to the time when they formed most of their mass.

A young but completely evolved galaxy, entirely self-built

Spectrum of the galaxy C1-23152. Credit: National Institute of Astrophysics

Seventeen hours of spectroscopic observations of the elliptical galaxy C1-23152 with the Large Binocular Telescope (LBT) allowed Saracco’s team to reconstruct its evolutionary history at a time when the universe was less than 13% of its current age. “The data show that the time of formation of C1-23152, that is, the time elapsed between the formation of the first stars from the pre-existing gas to the time when star formation had almost completely ceased, is less than 500 million years,” says Paolo Saracco, researcher at INAF of Milan and first author of the article published on The Astrophysical Journal. “Furthermore, from the data collected with LBT, we were able to establish that in this short time, corresponding to less than four hundredths of the age of the universe, the galaxy has formed a mass equal to about 200 billion stars like the sun, that is, about 450 alone a year. Our galaxy, the Milky Way, now forms no more than two a year, “adds Danilo Marchesini, full professor at Tufts University and second author of the article. Furthermore, the large amount of information gathered allowed the team to quantify the abundance of chemical elements heavier than helium (the so-called metallicity) for the first time in such a distant galaxy: the stars of this galaxy have, surprisingly, a higher metallicity than that of the sun, similar to that observed in the most massive galaxies in the universe today.

“These observations have shown that the formation of the most massive galaxies in the universe can occur extremely rapidly, through an extremely intense star formation process in the early universe, as for C1-23152,” says Francesco La Barbera, researcher of the INAF of Naples.

A young but completely evolved galaxy, entirely self-built

Probable scenario of the formation of huge elliptical galaxies such as C1-23152. Massive primordial gas clouds, which fall in the same region under the effect of gravitational force, collide, triggering violent and massive star formation processes. The starburst phase is expected to last a few hundred million years during which hundreds to thousands of stars are formed per year, as per C1-23152. The resulting massive elliptical galaxy will then evolve over time, likely experiencing several evolutionary phenomena. Credit: National Institute of Astrophysics

“Understanding whether the scenario describing the formation of C1-23152 is a particular case or if, on the contrary, it is what happens for most of the most massive galaxies in the universe, is of fundamental importance, as this would require a profound revision. of galaxy formation models “, adds Adriana Gargiulo, also a researcher at INAF in Milan and co-author of the study.

A young but completely evolved galaxy, entirely self-built

This image shows an example of starburst galaxies that form around a thousand stars per year at the time of observation. This phase is most likely the phase of formation of massive galaxies in the early universe, such as C1-23152. Credit: National Institute of Astrophysics

The formation of high stellar masses as for C1-23152 requires both high masses of gas to convert into stars and particular physical conditions. A possible scenario hypothesized by the researchers is that massive primordial gas clouds, falling under the effect of gravitational force in the same region, collide, triggering violent and massive star formation processes. From the observational point of view, the precursors of the most massive galaxies could therefore be remote galaxies with a very high rate of star formation.

“To test our hypotheses, the observations that the next generation of instruments will allow us to carry out, in particular, the James Webb Space Telescope (JWST) which will be launched into orbit at the end of 2021, and the Extremely Large Telescope ( ELT) the largest terrestrial telescope ever built, with a main mirror of 39 meters in diameter, which will be operational in 2026 “, concludes Saracco.


Astronomers collect heavy metal to shed light on star formation


More information:
Paolo Saracco et al. The rapid accumulation of huge early type galaxies: supersolar metallicity, high speed scattering and young age for a primitive type galaxy z = 3.35, The Astrophysical Journal (2020). DOI: 10.3847 / 1538-4357 / abc7c4

Provided by the National Institute of Astrophysics

Quote: A young but fully evolved galaxy entirely self-built (2020, December 14) recovered on December 15, 2020 from https://phys.org/news/2020-12-young-evolved-self-made-galaxy.html

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