Discovery of young blazar produced by merger of two galaxies

A blazar is a particular type of active galactic nucleus (AGN) with a central supermassive black hole which emits a jet, a flux of highly energetic particles and radiation moving almost at the velocity of light, and which is aligned along the observer's line of sight. An international team of researchers has observed the birth of one of these objects for the first time by combining observations from several telescopes, among them the William Herschel Telescope (WHT).

As a point of reference, scientists believe all large galaxies have centrally located massive black holes, but only about one per cent of these have active nuclei. For example, our Milky Way's massive black hole is dormant. The emission from an AGN can often exceed that of the host galaxy and originates from the central black hole accreting circumnuclear gas. But not all this gas is accreted onto the black hole; some get accelerated and spewed out in the form of narrow, bipolar jets.

 

"Active galaxies which have jets are usually big, old elliptical galaxies which, according to the models, are formed by the merger of two or more smaller galaxies, so that we think that these mergers are the cause of the activation of the jets," said Ruben Garcia-Benito, a researcher at the Instituto de Astrofisica de Andalucia (IAA-CSIC), who participated in the discovery.

"A galactic collision is a very efficient way to make large masses of gas fall to the center of a galaxy, which feeds the supermassive black hole and can produce the emergence of the jet," Ruben added.

Now, astronomers have imaged the formation of a jet from two younger, spiral-shaped galaxies, in the process of merging. In scientific terminology, these young spiral galaxies containing jets are called narrow-line Seyfert 1 gamma-ray emitter galaxies (gamma-NLSy1).

Each merging galaxy shows a supermassive black hole at its center. The more massive of the two shows a very young jet, with an estimated age of less than 15,000 years, whose existence can be attributed to the interaction between the galaxies, which started at least 500 million years ago.

"We are seeing the jet face-on" explained Enrique Perez Jimenez, a researcher at the IAA-CSIC and a co-author of the study, "so that we have found the precursor of a blazar. As an analogy, we could say that if a blazar is an adult, a gamma-NLSy1 is a child."

Jets are the most powerful astrophysical phenomena in the universe. They can emit more energy into the universe in one second than our Sun will produce in its entire lifetime. That energy is in the form of radiation, such as intense radio waves, X-rays, and gamma-rays.

In general, blazars are so bright that they occult the galaxies which host them so that studying their environment is difficult.

However, the detected jet in this young galaxy is less energetic, which has permitted the study of the gas and the stars of the host galaxy, providing very valuable information to trace the origin of the jet.

The team obtained the image and the spectra using several of the largest ground-based telescopes in the world, such as the GTC and the WHT on La Palma, as well as the optical/infrared Subaru telescope on Hawaii, and NASA's Chandra X-ray satellite observatory. The WHT ISIS observations were obtained as part of a service programme.