According to a new study published this week in the Monthly Notices of the Royal Astronomical Society, a phenomenon called ram-pressure stripping is more prevalent than previously thought.
An artist’s impression showing the increasing effect of ram-pressure stripping in removing gas from the spiral galaxy NGC 4921 and its satellite galaxies. Image credit: ICRAR / NASA / ESA / Hubble Heritage Team / STScI / AURA.
The study of 10,567 galaxies shows that their gas — the lifeblood for star formation — is being violently stripped away on a widespread scale throughout the local Universe.
Lead author Toby Brown, an astronomer at the International Centre for Radio Astronomy Research and Swinburne University of Technology, and his colleagues used data from the Sloan Digital Sky Survey (SDSS) and the Arecibo Legacy Fast ALFA survey.
“The image we paint as astronomers is that galaxies are embedded in clouds of dark matter that we call dark matter halos,” Brown said.
“During their lifetimes, galaxies can inhabit halos of different sizes, ranging from masses typical of our own Milky Way Galaxy to halos thousands of times more massive.”
“As galaxies fall through these larger halos, the superheated intergalactic plasma between them removes their gas in a fast-acting process called ram-pressure stripping.”
According to the team, removing the gas from galaxies leaves them unable to form new stars.
“It dictates the life of the galaxy because the existing stars will cool off and grow old. If you remove the fuel for star formation then you effectively kill the galaxy and turn it into a dead object,” Brown explained.
“Scientists already knew ram-pressure stripping affected galaxies in clusters, which are the most massive halos found in the Universe,” said co-author Dr. Barbara Catinella, of ICRAR.
“We demonstrate that the same process is operating in much smaller groups of just a few galaxies together with much less dark matter,” Brown added.
“Most galaxies in the Universe live in these groups of between two and a hundred galaxies. We’ve found this removal of gas by stripping is potentially the dominant way galaxies are quenched by their surroundings, meaning their gas is removed and star formation shuts down.”
“The other main process by which galaxies run out of gas and die is known as strangulation.”
“Strangulation occurs when the gas is consumed to make stars faster than it’s being replenished, so the galaxy starves to death. It’s a slow-acting process,” Brown said.
“On the contrary, what ram-pressure stripping does is bop the galaxy on the head and remove its gas very quickly — of the order of tens of millions of years — and astronomically speaking that’s very fast.”
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Toby Brown et al. 2017. Cold gas stripping in satellite galaxies: from pairs to clusters. MNRAS 466 (2): 1275-1289; doi: 10.1093/mnras/stw2991
This article is based on a press-release from the International Centre for Radio Astronomy Research.
