A young but fully developed galaxy, made entirely of itself

Color image of galaxy C1-23152 at redshift 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 an ordinary spheroidal galaxy, its light profile matches those of typical elliptical galaxies in the local universe. Its star mass is about 200 billion stars like the sun and formed in less than 500 million years. Credit: National Institute of Astrophysics

So young and already so evolved: Thanks to observations from the Large Binocular Telescope, an international team of researchers led by Paolo Saracco of the Istituto Nazionale di Astrofisica (INAF, Italy) has managed to reconstruct the history of the wild evolution of an extremely massive galaxy. which existed 12 billion years ago, when the universe was only 1.8 billion years old, less than 13% of its current age. This galaxy, nicknamed C1-23152, formed in just 500 million years, an incredibly short time to give rise to a mass of about 200 billion suns. To do this, it has produced up to 450 stars a year, more than once a 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 to galaxy formation patterns for objects for which it is currently difficult to give.

The most massive galaxies in the universe reach masses of several hundred billion times that of the sun, and although they are numerically only a 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 questions 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 subsequent mergers of pre-existing smaller 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 formed in early epochs. Unfortunately, the variety of evolutionary phenomena that galaxies can undergo during their lifetime does not allow astronomers to define how they formed, leaving large margins of uncertainty. However, an answer to these questions may come from the study of 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 fully developed galaxy, made entirely of itself

Galaxy Spectrum C1-23152. Credit: National Institute of Astrophysics

Seventeen hours of spectroscopic observations of the C1-23152 elliptical galaxy with the Large Binocular Telescope (LBT) allowed Saracco’s team to reconstruct its history of evolution at a time when the universe was below 13% of its current age. “The data show that the formation time of C1-23152, ie the time elapsed between the formation of the first stars from the pre-existing gas until the time when star formation ceased almost completely, is less than 500 million years,” says Paolo Saracco, researcher at INAF in Milan and the first author of the article published in The astrophysics journal. “Also, from the data collected with LBT, we were able to establish that in this short time, which corresponds to less than four hundredths of the age of the universe, the galaxy formed a mass equal to about 200 billion stars as the sun, ie about 450 sunshine a year. Our Milky Way galaxy now forms no more than two a year, “added Danilo Marchesini, a tenured professor at Tufts University and the second author of the article. In addition, the large amount of information collected allowed the team to quantify the abundance of more chemical elements. heavier than helium (so-called metallicity) for the first time in such a distant galaxy: The stars in this galaxy are surprisingly more metallic than the sun, similar to that seen 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 take place extremely quickly, through an extremely intense star formation process in the early universe, as for C1-23152,” says Francesco La Barbera, a researcher at INAF from Naples.

A young but fully developed galaxy, made entirely of itself

Probable scenario for the formation of massive elliptical galaxies such as C1-23152. Massive clouds of primordial gases, which fall in the same region under the effect of gravitational force, collide, triggering violent and massive star-forming processes. The phase of the star explosion is expected to last several hundred million years, during which time hundreds to thousands of stars form each year, as for C1-23152. The resulting massive elliptical galaxy will then evolve over time, possibly experiencing various evolutionary phenomena. Credit: National Institute of Astrophysics

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

A young but fully developed galaxy, made entirely of itself

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

The formation of stellar masses as high as C1-23152 requires both large masses of gas to turn into stars and particular physical conditions. A possible scenario hypothesized by researchers is that massive clouds of primordial gases, which fall under the effect of gravitational force in the same region, collide, triggering violent and massive star-forming processes. Observationally, the precursors of the most massive galaxies could therefore be distant 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 make will be decisive, especially the James Webb Space Telescope (JWST) which will be launched into orbit at the end of 2021 and the Extremely Large Telescope (ELT) the most The largest terrestrial telescope ever built with a 39-meter-diameter main mirror that will be operational in 2026, “concludes Saracco.


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More information:
Paolo Saracco et al. Rapid development of early massive galaxies: supersolar metallicity, high-velocity dispersion and young age for an early-type galaxy at z = 3.35, The astrophysics journal (2020). DOI: 10.3847 / 1538-4357 / abc7c4

Provided by the National Institute of Astrophysics

Citation: A young but fully developed, self-made galaxy (2020, December 14), retrieved on December 15, 2020 from https://phys.org/news/2020-12-young-evolved-self-made- galaxy.html

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