Astronomers using the NASA/ESA Hubble Space Telescope have observed clumps of star formation in the tails and disks of six ram-pressure stripped (jellyfish) galaxies.
This Hubble image shows JO201 (also known as Ka 364, LEDA 2456 and LEDA 93189), a jellyfish galaxy located in the constellation of Cetus. Image credit: NASA / ESA / Hubble / M. Gullieuszik.
Understanding the physical conditions that lead to the formation of new stars, and conversely to the halting of the star formation activity, is central for astrophysics.
Galaxy disks are the usual cradle for star formation. This is a hierarchical process traced by star-forming regions, dubbed clumps, which are ubiquitous in star-forming galaxies.
Extremely distant galaxies are dominated by bright clumps, which are larger and more massive than in the local Universe.
The star formation activity is strongly influenced and can be even halted by a number of processes, some of which are directly related to the environment in which the galaxy resides.
Ram pressure stripping, i.e. the removal of interstellar gas from the disk of star forming galaxies due to the hydrodynamical interaction with the hot intergalactic medium, is one such process and it is believed to have a strong impact on galaxy populations in dense environments such as galaxy groups and, especially, clusters.
“As jellyfish (ram-pressure stripped) galaxies move through intergalactic space they are slowly stripped of gas, which trails behind the galaxy in tendrils illuminated by clumps of star formation,” said Dr. Marco Gullieuszik from the INAF-Osservatorio astronomico di Padova and colleagues.
“These blue tendrils are visible drifting below the core of a galaxy in the Hubble image, and give it its jellyfish-like appearance.”
“This particular jellyfish galaxy — known as JO201 — lies in the constellation Cetus, which is named after a sea monster from ancient Greek mythology.”
“This sea-monster-themed constellation adds to the nautical theme of the image.”
In their study, the astronomers used Hubble to study star-forming clumps in JO201 and five other jellyfish galaxies.
They detected over 3,700 clumps in the disks, 1,200 clumps in the extraplanar regions, and over 1,200 clumps in the tails of these galaxies.
Only 15% of the star-forming clumps were spatially resolved, meaning that most are smaller than 500 light-years.
“We found clear signatures of stripping in regions very close in projection to the galactic disk,” the authors said.
“The star-forming regions in the stripped tails are extremely bright and compact.”
“We hope that our results will provide a breakthrough in understanding the connection between ram-pressure stripping — the process that creates the tendrils of jellyfish galaxies — and star formation,” they concluded.
The findings appear in two papers in the Astrophysical Journal.
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Marco Gullieuszik et al. 2023. UV and Hα HST observations of 6 GASP jellyfish galaxies. ApJ, in press; arXiv: 2301.08279
Eric Giunchi et al. 2023. HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxies. ApJ, in press; arXiv: 2302.10615
