Abell’s Orphan Cloud 1367 (Cosmology)

It is an immense cloud of hot gas first discovered in 2017 by the Japanese Subaru telescope in the intergalactic medium of the Abell 1367 cluster. It is an isolated cloud, not associated with any galaxy in the cluster. New observations conducted with the Subaru telescope, with the Vlt and Xmm-Newton have now made it possible to measure different properties, to identify its origin and the mechanism that allowed it to fluctuate between galaxies, making its existence surprising. All details in Monthly Notices of the Royal Astronomical Society

The galaxy clusters are among the largest celestial objects of the universe: they can contain from tens to thousands of galaxies held together by gravity and extend for millions of light years. Abell 1367 is one of them. It is a young cluster of about 70 galaxies located 300 million light years from Earth in the constellation of Leo . In 2017, using data obtained from the Japanese Subaru telescope in Mauna Kea, Hawaii, a team of astronomers discovered something strange inside: a small cloud of hot gas isolated and not associated with any galaxy in the cluster. In short, an orphan cloud.

Now, thanks to new observations made using the ESA Xmm-Newton X-ray telescope , the same Subaru telescope and ESO ‘s Very Large Telescope (Vlt), a team of astronomers led by the University of Alabama at Huntsville ( Usa) has measured some salient features, discovering that the cloud is actually larger than the Milky Way and that the gas it is made of has a different origin from that of the medium in which it is located. These are the first observations of a mass of intracluster hot gas detected both in X-rays and in visible light.

The cloud in question is the umbrella-shaped structure you see in the opening image highlighted in blue, the color associated with the energy of the X radiation emitted by the gas in the cloud and captured by Xmm-Newton. In the article published in Monthly Notice of the Royal Astronomical Society, the authors describe it as a cloud with a mass equal to about 10 billion times that of the Sun, made of interstellar gas torn away from a galaxy of the cluster and “stranded” in the space between galaxies permeated by intracluster medium – plasma superheated to millions of degrees.

Its temperature suggests that the gas comes from intragalactic. The interstellar medium is much colder than the intergalactic medium, the researchers explain, and the temperature of the orphan cloud matches that of the interstellar gas. Gas that may have been blown out of the galaxy as it moved through the cluster, then floated for a long time in the space between galaxies, making its simple survival surprising, the researchers note.

And speaking of survival, the authors of the study were also able to determine what allowed the orphan cloud to last for so long: the merit would be of its magnetic field, able to counteract instabilities caused by differences in speed and density of the interstellar hot gas versus intracluster plasma . As for the mother galaxy that originated the cloud, considering the enormous mass of gas it is made of, according to the researchers it is probably a massive galaxy, whose name could be discovered with future observations.

This study paves the way for the search for intracluster clusters , the researchers conclude, as future hot gas investigations can now be aimed at looking for other orphan clouds.

Featured image: Three-color composite image of the X-band and visible emission of the region around the Abell 1367 orphan cloud. In blue, the X-ray emission of the cloud. In red the emission of hot gas. In white the optical emission of some of the galaxies in the cluster. Credits: Chong Ge et al., 2021

To know more:

  • Read on Monthly Notices of the Royal Astronomical Society the article ” An H α / X-ray orphan cloud as a signpost of intracluster medium clumping ” by Chong Ge, Rongxin Luo, Ming Sun, Masafumi Yagi, Pavel Jáchym, Alessandro Boselli, Matteo Fossati, Paul EJ Nulsen, Craig Sarazin, Tim Edge, Giuseppe Gavazzi, Massimo Gaspari, Jin Koda, Yutaka Komiyama and Michitoshi Yoshida

Provided by INAF

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