Spin flips show how galaxies grow out of the cosmic web

Examples of SAMI galaxies with central bulge and surrounding disk. Credit: Hyper Supreme-Cam Subaru and Pan-STARSS

The alignment between the spins of galaxies and the large-scale structure of the universe reveals the processes by which the different components of galaxies are formed.

The large-scale structure of the universe is traced by the distribution of galaxies. This “cosmic web” is made up of gigantic filamentous structures that connect huge clusters of galaxies.

A new study published in Royal Astronomical Society Monthly Notices finds that galaxies with larger bulges tend to rotate perpendicular to the filaments in which they are embedded, while galaxies with smaller bulges tend to rotate parallel to these filaments.

“It all refers to the mass of the bulge,” says astrophysicist Dr. Stefania Barsanti of the Australian National University, lead author of the paper and a member of the ASTRO 3D Center of Excellence.

“Galaxies that are mostly disks, with a low-mass bulge, tend to have their axis of rotation parallel to the nearest filament. This is because they are formed mainly from gas that falls on the filament and” coils “it. galaxies grow as galaxies merge, generally as they move along the filament. Thus, mergers also tend to “flip” the alignment between the rotation of the galaxy and the filament from parallel to perpendicular.

‘We think mergers should be more likely as galaxies move along the filaments towards each other. The direction of these mergers drives the spin flip,’ says Prof. Scott Croom, University of Sydney astronomer and co-author of the article.

This discovery sheds light on the formation of two major components of galaxies and how they relate to large-scale structures and the movements of matter in the cosmic web.

“Our motivation was to try to understand why galaxies rotate and how they acquire their angular momentum from the material that forms them,” says Dr. Barsanti.

“Through this study, we can understand how mergers play an important role in the formation of galaxies, both the central component of the bulge and the spin flipping,” he says. “This points to particular formation channels for how galaxies begin to rotate and how the rotation changes as the galaxy evolves.”

Although this evolution was suggested by computer simulations, this study is the first time that scientists have used direct observation to confirm that the growth of a galaxy’s central bulge can cause it to flip alignments.

“This is a subtle signal that is really hard to detect in observations,” says Dr. Barsanti.

It was made possible with the advent of integral field spectroscopy, a technique in which an optical instrument combines spectrographic and imaging capabilities to construct a 3D image of a galaxy and at the same time resolve its internal movements.

This study used a spectroscope called SAMI, connected to the 3.9-meter-wide Anglo-Australian telescope located in Siding Spring, New South Wales.

The researchers used SAMI to examine 3,068 galaxies between 2013 and 2020. This staggering amount of data took years to study and provided direct evidence for the published article.

“With the SAMI Galaxy Survey we solved the space spectroscopy that allowed us to map the galaxy, with spectra in many places in the galaxy,” says Dr. Barsanti. “This tells us the internal movements of the stars and gas within the galaxy, so we can measure their overall rotation. These results will inform the next big phase of our research, the Hector Galaxy Survey. Hector is the next generation spectrograph that replaces SAMI at the Anglo-Australian Telescope, which we will use to detect about 30,000 galaxies. “

Professor Stuart Wyithe of the University of Melbourne, who is Director of ASTRO 3D, says the paper promotes the Center’s key objectives of tracing the distribution of matter from the earliest times in the universe to the present day and to construct a 3D image of the formation and evolution of the universe we see today.

“Using the power of the SAMI galaxy survey, which measured the 3D structure of individual galaxies and their position in space, this paper shows how the mass movements in galaxies and the positions of galaxies are connected, which is an essential piece. to understand how galaxies came together, “says Professor Wyithe

The study was conducted in collaboration with researchers from the Australian National University, the University of Sydney, Johns Hopkins University, the University of Hamburg, the University of Cambridge and Macquarie University.

Because huge galaxies don’t dance in a crowd

More information:
Stefania Barsanti et al, The SAMI Galaxy Survey: Spin-filament alignment reversal is closely related to bulge growth, Royal Astronomical Society Monthly Notices (2022). DOI: 10.1093 / mnras / stac2405

Provided by ARC Center of Excellence for All Sky Astrophysics in 3D (ASTRO 3D)

Citation: Spin flips show how galaxies grow from the cosmic web (2022, October 4) retrieved October 4, 2022 from https://phys.org/news/2022-10-flips-galaxies-cosmic-web.html

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