6.12.2024

Figure 1: Schematic diagram shows how spheroid formation occurs in distant submillimetre-bright galaxies, and how this process connects to the evolution of giant elliptical galaxies in today's Universe. On the far left, we have RGB images from JWST (using F444W for red, F227W for green, and F150W for blue) showcasing examples from our sample of galaxies. The cyan dashed ellipse marks the concentrated region of submm emission, with zoomed-in views highlighting the ALMA submm images. Also shown is a classification of the galaxies' intrinsic shapes. The average shape parameters for our full sample (green ellipse), a subsample of submm-compact galaxies (orange ellipse), and a subsample of submm-extended galaxies (blue ellipse) are compared to local early-type galaxies (red ellipse) and late-type galaxies (represented by purple and cyan spiral shapes). (Credit: Qing-Hua Tan)

An international team of researchers including The University of Tokyo Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU, WPI) has found evidence showing that old elliptical galaxies in the universe can form from intense star formation within early galaxy cores. This discovery that will deepen our understanding of how galaxies evolved from the early Universe, reports a new study in Nature.

Galaxies in today’s Universe are diverse in morphologies and can be roughly divided into two categories: younger, disk-like spiral galaxies, like our own Milky Way, that are still forming new stars; and older, elliptical galaxies, which are dominated by a central bulge, no longer forming stars and mostly lacking gas. These spheroidal galaxies contain very old stars, yet how they formed has remained a mystery—until now.

The discovery of the birth sites of giant, elliptical galaxies – announced in a paper published today in the Nature – come from analyzing data from the Atacama Large Millimeter/submillimeter Array (ALMA) on over 100 Submillimeter Bright Galaxies (SMGs) with redshifts dating to the “Cosmic noon” era, when the universe was between around 1.6 and 5.9 billion years old and many galaxies were actively forming stars. This study provides the first solid observational evidence that spheroids can form directly through intense star formation within the cores of highly luminous starburst galaxies in the early Universe, based on a new perspective from the submillimeter band. This breakthrough will significantly impact models of galaxy evolution and deepen our understanding of how galaxies form and evolve across the Universe.

In this study, researchers led by Chinese Academy of Sciences Purple Mountain Observatory Associate Researcher Qinghua Tan, and including Kavli IPMU Professor John Silverman, Project Researcher Boris Kalita, and graduate student Zhaoxuan Liu, used statistical analysis of the surface brightness distribution of dust emission in the submillimeter band, combined with a novel analysis technique. They found that the submillimeter emission in most of sample galaxies are very compact, with surface brightness profiles deviating significantly from those of exponential disks. This suggests that the submillimeter emission typically comes from structures that are already spheroid-like. Further evidence for this spheroidal shape comes from a detailed analysis of galaxies’ 3D geometry. Modeling based on the skewed-high axis-ratio distribution shows that the ratio of the shortest to the longest of their three axes is, on average, half and increases with spatial compactness. This indicates that most of these highly star-forming galaxies are intrinsically spherical rather than disk-shaped. Supported by numerical simulations, this discovery has shown us that the main mechanism behind the formation of these tri-dimensional galaxies (spheroids) is the simultaneous action of cold gas accretion and galaxy interactions. This process is thought to have been quite common in the early Universe, during the period when most spheroids were forming. It could redefine how we understand galaxy formation.

This research was made possible thanks to the A3COSMOS and A3GOODSS archival projects, which enabled researchers to gather a large number of galaxies observed with a high enough signal-to-noise ratio for detailed analysis. Future exploration of the wealth of ALMA observations accumulated over the years, along with new submillimeter and millimeter observations with higher resolution and sensitivity, will allow us to systematically study the cold gas in galaxies. This will offer unprecedented insight into the distribution and kinematics of the raw materials fueling star formation. With the powerful capabilities of Euclid, the James Webb Space Telescope (JWST), and the China Space Station Telescope (CSST) to map the stellar components of galaxies, we will gain a more complete picture of early galaxy formation. Together, these insights will deepen our understanding of how the Universe as a whole has evolved over time.

Paper details
Journal: Nature
Paper title: In-Situ Spheroid Formation in Distant Submillimeter-Bright Galaxies
Authors: Qing-Hua Tan (1,2), Emanuele Daddi (2), Benjamin Magnelli (2), Camila A. Correa (2), Frédéric Bournaud (2), Sylvia Adscheid (3), Shao-Bo Zhang (1), David Elbaz (2), Carlos Gómez-Guijarro (2), Boris S. Kalita (4,5,6), Daizhong Liu (1), Zhaoxuan Liu (4,5,7), Jérôme Pety (8,9), Annagrazia Puglisi (10,11), Eva Schinnerer (12), John D. Silverman (4,5,7,13), Francesco Valentino (14,15)

Author affiliations:
1. Purple Mountain Observatory, Chinese Academy of Sciences, 10 Yuanhua Road, Nanjing 210023, People's Republic of China
2. Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Gif-sur-Yvette 91191, France
3. Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
4. Kavli Institute for the Physics and Mathematics of the Universe, The University of Tokyo, Kashiwa, 277-8583, Japan
5. Center for Data-Driven Discovery, Kavli IPMU (WPI), UTIAS, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan
6. Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, People's Republic of China
7. Department of Astronomy, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan
8. Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, 38406 Saint-Martin d’Hères, France
9. LERMA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, 75014 Paris, France
10. School of Physics and Astronomy, University of Southampton, Highfield SO17 1BJ, UK
11. Center for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
12. Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
13. Center for Astrophysical Sciences, Department of Physics & Astronomy, Johns Hopkins University, Baltimore, MD 21218, USA
14. European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei Munchen, Germany
15. Cosmic Dawn Center (DAWN), Denmark

Quelle: Kavli Institute for the Physics and Mathematics of the Universe
The University of Tokyo