How quasars influence the evolution of galaxies

Astronomers have explored the most remote regions of space to study how quasars, among the brightest sources of the Universe, influence the evolution of galaxies. The numerical simulations relating to the dynamics of the gas which is ejected at high speed from the central regions of the quasar are consistent with observations obtained, in particular, in the case of SDSS J1148 + 5251, a bright object which is located almost 13 billion light years. The results are published in the journals of Monthly Notices of the Royal Astronomical Society and Astronomy & Astrophysics.
Two teams of astronomers led by colleagues at the University of Cambridge have explored the deep space to a distance so remote that corresponds to a time when the universe was one under a billion years. The goal is to determine how quasars have adjusted the birth of stars and the formation of galaxies more massive.


Credit: Tiago Costa/AAAS

Quasars are among the brightest sources of the Universe and those further away are so remote that allow us to go back in time billions of years. These objects are powered by the activity of supermassive holes blacks residing in the nuclei of galaxies and are surrounded by a region of gas-shaped disk that orbits the black holes at high speed. As the black hole captures matter from the surrounding space is released a huge amount of energy.
With the data collected with the IRAM Plateau de Bure interferometer and those obtained by numerical simulations made with the supercomputer, the researchers found that a quasar emits cold gas at high speed, up to 2000 km / sec, reaching distances of almost 200 000 light years, much higher than has been observed so far. “It’s the first time we are seeing such a flow of cold gas at these speeds and distances from these massive central black hole,” says Claudia Cicone, doctoral student at the Cavendish Laboratory in Cambridge, affiliated with the Kavli Institute for Cosmology, and lead author of one of the two articles. “It is very difficult that the gas at such low temperatures is moving at high speeds as well as those that measure.”
The causes that determine this acceleration at such high speeds of the cold gas, which is a kind of raw material needed to generate the new stars, still remain a mystery. The detailed analysis that derives from a comparison between observations and simulations allowed us to understand just how this process happens: the gas is initially heated up to temperatures of the order of 10 million degrees, thanks to the energy emitted by the supermassive black hole that powers the quasar. Consequently, the enormous pressure buildup accelerates the hot gas and pushes it to the outer regions of the galaxy.


Credit: Tiago Costa/AAAS

The observations of Cicone allowed to a second group of researchers, specialists of numerical simulations, to develop a model which allows to describe the flow of gas in the quasar. The simulations show that during the escape from the galaxy, the gas has enough time to cool down to the point of reaching temperatures such that it becomes visible to radio telescopes in the millimeter band.
“While the super-hot gas is ejected from the quasar, part of it has enough time to cool down through a process similar to that with which radiative lowers the temperature of the Earth during a cloudless night,” says Tiago Costa, doctoral student of ‘Institute of Astronomers of Cambridge and the Kavli Institute for Cosmology, lead author of the second article. “The amazing thing is that in this primordial galaxy conditions are just the right ones to allow the hot gas to have time to cool down as it was found by the group of Claudia Cicone” concludes Costa.

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