A research team led by International Centre for Radio Astronomy Research (ICRAR) astronomers has studied the molecular-gas content of nearby massive galaxies in a cosmological simulation, focusing on how it depends on galaxy environment.
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.
“Our study provides new systematic evidence that small galaxies everywhere lose some of their molecular gas when they get close to a larger galaxy and its surrounding hot gas halo,” said Dr. Adam Stevens, an astrophysicist at ICRAR and the ARC Centre of Excellence in All Sky Astrophysics in 3 Dimensions (ASTRO 3D).
“Gas is the lifeblood of a galaxy. Continuing to acquire gas is how galaxies grow and form stars. Without it, galaxies stagnate.”
“We’ve known for a long time that big galaxies strip atomic gas from the outskirts of small galaxies. But, until now, it hadn’t been tested with molecular gas in the same detail.”
“Galaxies don’t typically live in isolation. When a galaxy moves through the hot intergalactic medium or galaxy halo, some of the cold gas in the galaxy is stripped away. This fast-acting process is known as ram pressure stripping,” said Dr. Barbara Catinella, also of ICRAR.
Using the TNG100 cosmological, hydrodynamic simulation, the astronomers made direct predictions for the amount of atomic and molecular gas that should be observed by specific surveys on the Arecibo telescope in Puerto Rico and the IRAM 30-m telescope in Spain.
They then took the actual observations from the telescopes and compared them to their original predictions. The two were remarkably close.
“The IRAM 30-m telescope observed the molecular gas in more than 500 galaxies,” Dr. Catinella said.
“These are the deepest observations and largest sample of atomic and molecular gas in the local Universe. That’s why it was the best sample to do this analysis.”
The finding fits with previous evidence that suggests satellite galaxies have lower star formation rates.
“Stripped gas initially goes into the space around the larger galaxy,” Dr. Stevens said.
“That may end up eventually raining down onto the bigger galaxy, or it might end up just staying out in its surroundings.”
“But in most cases, the little galaxy is doomed to merge with the larger one anyway.”
“Often they only survive for one to two billion years and then they’ll end up merging with the central one. So it affects how much gas they’ve got by the time they merge, which then will affect the evolution of the big system as well.”
“Once galaxies get big enough, they start to rely on getting more matter from the cannibalism of smaller galaxies.”
The study was published in the Monthly Notices of the Royal Astronomical Society.
Adam R.H. Stevens et al. 2021. Molecular hydrogen in IllustrisTNG galaxies: carefully comparing signatures of environment with local CO and SFR data. MNRAS 502 (3): 3158-3178; doi: 10.1093/mnras/staa3662