An international team of researchers have found evidence for a compact radio jet inducing turbulence and increasing the gas temperature as it progresses throughout the interstellar medium of the Teacup galaxy. The study has been led by Dr. Anelise Audibert and Dr. Cristina Ramos Almeida at the Instituto de Astrofísica de Canarias (IAC), Canary Islands, Spain. The work involved co-authors Ms. Meenakshi and Prof. Dipanjan Mukherjee from IUCAA, India, who using results from their hydrodynamical simulations, have provided the theoretical interpretation of the astronomical observations carried out by the international collaboration using the ALMA telescope in Chile. These findings are published today in the journal Astronomy & Astrophysics Letters (link).
When matter falls into a supermassive black hole in the centre of the galaxy, it unleashes enormous amounts of energy, and we say the galaxy has an active nucleus (or AGN). A fraction of AGN releases part of this energy as jets that are detectable in radio wavelengths and are traveling at relativistic velocities.
As long as the jet travels into the galaxy, it will collide with the clouds of gas in the galaxy and in some cases, push this material away in the form of a wind. However, it is still poorly understood what are the conditions that favour the blowing of winds in galaxies.
The effect of jets from supermassive blackholes impacting the content of the galaxies, like the stars, dust, and gas, is an important ingredient in the prescription of how galaxies evolve in the Universe.
So far, such effects have been studied for more powerful radio jets, hosted in so called ‘radio-loud’ galaxies. Such jets are thought to strongly affect the fate of the galaxies, although indirectly. They heat the galactic atmospheres, which prevents fresh supply of gas to the galaxy, thus restricting it from forming stars. But nowadays we are starting to discover that such jets can also have a more direct impact on the galaxies by interacting with the gas inside the galaxy itself. This is true even in the case of galaxies hosting more timid jets, known as ‘radio-quiet’ galaxies
, where the jets, though weaker, can cause a substantial disturbance.
Computer simulations of jets performed with advanced numerical codes predict that jets with velocities close to the light speed piercing into a galaxy can alter the shape of the gas as they penetrate further in the galaxy. One of the key elements to make the jets efficient in driving winds is the angle between the gaseous disk and the jet’s propagation. It has been observed that the jet’s coupling with their surrounding medium is enhanced with lowering the angle between the jet and the disk plane which keeps the jet trapped inside the host galaxy for a long duration.
Moreover, less-powerful jets, like the ones in ‘radio-quiet’ galaxies are likely to disturb the gas in a wider regions of their surrounding medium than the very powerful ones, which may relatively escape easily by drilling a narrow hole.
The results from this study:
An international scientific team led by the IAC discovered a perfect case to study the interaction of the radio jet with the cold gas around a massive quasar, named the Teacup
galaxy. The Teacup is a radio-quiet quasar located 1.3 billion light years from us and its nickname comes from the expanding bubbles seen in the optical and radio images, which resembles the handle of the tea cup. In addition, the central kiloparsec (around 3300 light years) hosts a compact and young radio jet that has a small inclination relative to the galaxy disk.
Using observations performed with the telescope in the Chilean desert, the Atacama Large millimetre/submillimetre Array (ALMA), the work led by the IAC researcher Anelise Audibert was able to capture the emission from the dense and cold gas in the Teacup, traced by two carbon monoxide molecules. Based on these observations, we find that the compact jet is clearly perturbing the gas distribution, clearing out the gas from the centre and pushing it away, despite the fact that it is a low-power jet.
Not only does the jet stir the gas in the Teacup, but also the motion of the cold gas is found to be accelerated by the jet in an unusual way. We expected to detect extreme conditions in the regions along the jet’s impact. However, when we looked at the observations, we found that the cold gas is turbulent and warmer in the directions perpendicular to the jet’s propagation
. Although such phenomenon have been detected in a handful of systems for hotter ionised gas, this is one of the first detection for the similar effect in cold, denser gas. “This is caused by shocks from a bubble produced by the jet that heats up and blows the gas in its lateral expansion away from the jet”, explains A. Audibert.
Our findings are supported by the comparison with high resolution hydrodynamic simulations performed by an international team of experts led by Prof. D. Mukherjee, from IUCAA. The simulations indicate that the orientation between the cold disk and the jet is a crucial factor in efficiently driving these lateral winds. The results from the simulation, when analysed by Ms. Meenakshi, showed excellent match with the observations, thus confirming the theoretical models. “Low-power jets were once believed to have a negligible impact in the galaxy, but our results show that even in the case of radio-quiet galaxies the jet is redistributing mass, metals, and preventing further star formation”
, says Cristina Ramos Almeida, an IAC researcher and co-author of the study.