For the first time, astronomers have detected the presence of CH+ — an ion of the CH molecule known as methylidynium to chemists — in distant starburst galaxies.
This image shows how gas falling into distant starburst galaxies ends up in vast turbulent reservoirs of cool gas extending 30,000 light-years from the central regions. Image credit: L. Benassi / ESO.
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of astronomers detected CH+ emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts 2.1 to 2.5, including the Eyelash galaxy (also known as SMM J2135-0102).
“CH+ is a special molecule,” said Dr. Martin Zwaan, an astronomer at ESO.
“It needs a lot of energy to form and is very reactive, which means its lifetime is very short and it can’t be transported far. CH+ therefore traces how energy flows in the galaxies and their surroundings.”
How CH+ traces energy can be thought of by analogy to being on a boat in a tropical ocean on a dark, moonless night. When the conditions are right, fluorescent plankton can light up around the boat as it sails.
The turbulence caused by the boat sliding through the water excites the plankton to emit light, which reveals the existence of the turbulent regions in the underlying dark water.
Since CH+ forms exclusively in small areas where turbulent motions of gas dissipate, its detection in essence traces energy on a galactic scale.
This ALMA image shows the Eyelash galaxy, a remote starburst galaxy that appears double and brightened by gravitational lensing. ALMA has been used to detect turbulent reservoirs of cold gas surrounding this and other distant starburst galaxies. By detecting CH+ for the first time in the distant Universe, this research opens up a new window of exploration into a critical epoch of star formation. Image credit: ALMA / ESO / NAOJ / NRAO / E. Falgarone et al.
The observed CH+ reveals dense shock waves, powered by hot, fast galactic winds originating inside the galaxies’ star-forming regions.
These winds flow through a galaxy, and push material out of it, but their turbulent motions are such that part of the material can be re-captured by the gravitational pull of the galaxy itself.
This material gathers into huge turbulent reservoirs of cool, low-density gas, extending more than 30,000 light-years from the galaxy’s star forming region.
“With CH+, we learn that energy is stored within vast galaxy-sized winds and ends up as turbulent motions in previously unseen reservoirs of cold gas surrounding the galaxy,” said Dr. Edith Falgarone, from the Ecole Normale Supérieure and Observatoire de Paris in France.
“Our results challenge the theory of galaxy evolution. By driving turbulence in the reservoirs, these galactic winds extend the starburst phase instead of quenching it.”
The astronomers determined that galactic winds alone could not replenish the newly revealed gaseous reservoirs.
They suggest that the mass is provided by galactic mergers or accretion from hidden streams of gas, as predicted by current theory.
“This discovery represents a major step forward in our understanding of how the inflow of material is regulated around the most intense starburst galaxies in the early Universe,” said Dr. Rob Ivison, ESO’s Director for Science.
The findings were published in the August 24, 2017 issue of the journal Nature.
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E. Falgarone et al. 2017. Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies. Nature 548: 430-433; doi: 10.1038/nature23298
