The Battle of the Titans

With the instrument CanariCam, mounted on the Gran Telescopio Canarias (GTC), the team of researchers known as ‘Los Piratas’ studied a system of two colliding galaxies that feed two blacks holes at their center.

Arp 299


What unites the two galaxies in collision with pirates? Much more than you can imagine. Of course, we’re talking about the pirates that do not go around the seas to plunder ships. Their ‘ weapons ‘ are one of the most powerful telescopes in the world, the Gran Telescopio Canarias (GTC) with his spectroscope CanariCam, very powerful computers, and especially their minds. Yes, because ‘Los Piratas’ (the Pirates, in fact) is the nickname that it was given to a friendly group of astronomers from (Miguel Pereira Santaella, associated INAF) Italian, Spanish, Mexican, American, German, Chilean and British research institutes studied Arp 299, a pair of colliding galaxies (whose initials are respectively NGC3690 and IC694). The system, still in the early stages of the conflict, has the presence of an AGN (Active Galactic Nucleus – AGN) that hosts a black hole within each of the galaxies.

Penetrate into the heart of these dense regions is quite complicated. They’re largely surrounded by a huge ‘donut’ of gas and dust (the so-called bull) that blocks the release of the blacks holes, regardless of the gas and dust surrounding host galaxies. With tools like CanariCam and the great light-gathering ability of the Gran Telescopio Canarias, however, they are able to focus on the internal parts of these dense regions and understand what is going on inside of this curtain.

The interaction that is taking place in Arp 299 is started at least 750 million years ago, but the system, called LIRG (acronym for Luminous InfraRed Galaxies, bright galaxies in the infrared), is not yet fully united. The main source of its electromagnetic emission is intense activity of star formation taking place in the system. The regions affected by the phenomenon are the nuclei, the spiral arms and also the area of the collision of two galaxies.

“Previous studies have found activity in the nucleus of both galaxies,” said Almudena Alonso Herrero, head of the study published in the journal The Astrophysical Journal Letters. “But thanks to the high angular resolution of the spectroscopic data of CanariCam observations are improved by a factor of ten compared to the previous ones carried out in the mid-infrared. The data in our hands – concluded Herrero – reveal the presence of activity in the center of both nuclei.”

The mid-infrared emission from the nucleus of NGC3690 (Galaxy western) can be explained in terms of the reissuing of the dust in the torus heated by the active nucleus. On the other hand, the spectrum of the central region of IC694 (the eastern galaxy) shows the presence of polycyclic aromatic hydrocarbons originating in an incorporated area and indicates the presence of intense star formation activity in this region, as proved by the dust heated from the active nucleus.

Thanks to the work of the ‘Los Piratas’, for the first time, it was possible to identify and differentiate a mid-infrared emission of two active nuclei, which emit simultaneously in Arp 299. Arp 299 is therefore a useful case study to test the theoretical predictions of contemporary two active galactic nuclei during the early stages of galactic collision.

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