Astronomers observe gas re-accretion using ALMA data

Scientists have leveraged data gathered using the Atacama Large Millimeter/submillimeter Array (ALMA) in a new study. The information gathered suggests that previously displaced gases can re-accrete onto galaxies. That process can slow down the process of the galaxy dying from ram pressure stripping and could create unique structures more resistant to its effects.

Researcher William Cramer says that much of the previous work on ram pressure stripping of galaxies focused on the material that gets stripped out of the galaxy. In this new study, the researchers have found that some gas moves like a boomerang, being ejected out but circling around and falling back into its source. The study was based on data gathered by Hubble and ALMA at very high resolution allowing the researchers to study the phenomena.

Ram pressure stripping is a process that displaces gas inside galaxies, leaving them without the material needed to form new stars. As galaxies move through their galactic clusters, hot gas known as intra-cluster medium acts like a wind pushing gases out of the traveling galaxy. Over time, the once active star-forming galaxy starves and dies.

Ram pressure stripping can speed up the normal lifecycle of the galaxy and alter the amount of molecular gas inside it. That means the process is of interest to scientists who study the life, maturation, and death of galaxies. Previously, in simulations, it has been seen that not all gas being pushed by ram pressure stripping escapes the galaxy. Gas has to reach escape velocity to escape the galaxy altogether without falling back.

The re-accretion being observed is from clouds of gas pushed out of the galaxy by ram pressure stripping and didn't achieve escape velocity. Researcher Jeff Kenney says when trying to predict how fast the galaxy will stop forming stars and transform into a red or dead galaxy, you must understand how effective ram pressure is in stripping gas out. Having proof of this nature means more accurate timelines for the lifecycle of galaxies.