Galaxies stop forming stars influenced by their direction

Dec. 23 () –

A study of 5,000 galaxy clusters in the Universe up to 7 billion years ago reveals that galaxies that stop growing are unevenly distributed depending on the direction within the cluster.

This result, Made with the Subaru Telescope Ultra Wide Field Prime Focus Cameraindicates that the mechanism that stops the growth of galaxies within a galaxy cluster may be working in an anisotropic way –it offers different properties when examined or tested in different directions– , and captures a new aspect of the galaxy formation process.

Galaxies, which are collections of hundreds of billions of stars, grow by star-forming activities that produce stars from gas, but observed star formation of galaxies ranges from active to nearly quiescent.

Investigate under which conditions star formation is promoted or suppressed It is important to understand the growth process of galaxies.

Some galaxies exist alone, while others are grouped together. Within a group of galaxies, a large group of hundreds to thousands of galaxies is called a “galaxy cluster.” Galaxy clusters can extend up to three million light-years and are full of “galaxy cluster gas”, a hot gas with temperatures ranging from tens to hundreds of millions of degrees Celsius.

Interestingly, many galaxies that exist on their own are star-forming, while many galaxies in a galaxy cluster have stopped forming stars. This is thought to be due to the unique environment of galaxies and clusters of galaxies, which are densely packed with cluster gas, where the wind pressure of cluster gas and the gravity of other galaxies passing nearby are known to For example, they strip the gas – the material for stars – from the interior of a galaxy. As a result, the formation or star growth of galaxies is believed to cease.

Most of the previous studies focused on galaxy clusters have been based on the assumption that the properties of galaxies belonging to a cluster of galaxies are isotropic, that is, that the properties of galaxies are the same regardless of direction. in which it is examined from the center of the cluster.

However, recent research has indicated that the distribution of galaxies that have stopped growing may be skewed in certain directions within the cluster. Most galaxy clusters have a single giant galaxy (the central galaxy) at the center of the cluster, but it seems that quiescent galaxies are more often in the direction of the major axis of the central galaxy. This is interpreted as the galaxy’s ability to stop star formation within the cluster is strongest in the direction aligned with the central galaxy (long axis) and weakest in the direction perpendicular to it.

These suggestions are based on studies limited to the current Universe and on observations of a small sample of galaxy clusters. Therefore, it was not clear if this bias is universal over a wide range of ages in the Universe, or if it is a general trend observed in all galaxy clusters.

A team led by Makoto Ando, ​​a graduate student at the University of Tokyo, has studied more than 5,000 galaxy clusters captured by the Subaru telescope’s Hyper Suprime-Cam (Subaru Hyper Suprime-Cam Strategic Framework Program), a large-scale study scale of the Universe. The study investigated how the proportion of galaxies that have ceased star formation changes in relation to the orientation of the central galaxy.

They found that the proportion of star-forming galaxies is greatest along the long axis of the central galaxy and least perpendicular to it. Furthermore, this bias was detected in galaxy clusters up to about 7 billion years old, indicating that it is universal. The bias detected in this study is only a few percent, and was only detectable by statistical analysis of a large, high-quality sample of galaxy clusters from the Subaru Telescope, reports the Subaru Telescope in a statement.

“Thanks to the large, high-quality observational data from the Subaru Telescope, we have discovered a new aspect of the mechanism that stops the growth of galaxies in a galaxy cluster and its universality. However, we have not detected any direct evidence of it, as the activity of black holes or the uneven distribution of gas in galaxy clusters. These are expected to be clarified in the future by X-ray and radio observations. We believe that if we understand the cause of the bias of galaxies that have stopped growing , we will be able to approach the history of the growth of galaxies in clustersAndo says.