"Īlthough it is now clear that a galactic merger is almost certainly necessary for a galaxy to host a supermassive black hole with relativistic jets, the team deduce that there must be additional conditions which need to be met.
"About 40% of the other galaxies we looked at had also experienced a merger and yet had failed to produce the spectacular radio emissions and jets of their counterparts. "We found that most merger events in themselves do not actually result in the creation of AGNs with powerful radio emission, " added co-author Roberto Gilli from Osservatorio Astronomico di Bologna, Italy. However, it was not only the galaxies containing jets that showed evidence of mergers! ". "By using Hubble's WFC3 camera we found that almost all of the galaxies with large amounts of radio emission, implying the presence of jets, were associated with mergers. "The galaxies that host these relativistic jets give out large amounts of radiation at radio wavelengths, " explains Marco.
The team inspected five categories of galaxies for visible signs of recent or ongoing mergers – two types of galaxies with jets, two types of galaxies that had luminous cores but no jets, and a set of regular inactive galaxies. It is these jets that Marco Chiaberge from the Space Telescope Science Institute, USA (also affiliated with Johns Hopkins University, USA and INAF-IRA, Italy) and his team hoped to confirm were the result of galactic mergers. The hot material within the jets is also the origin of radio waves. The two high-speed jets of plasma move almost with the speed of light and stream out in opposite directions at right angles to the disc of matter surrounding the black hole, extending thousands of light-years into space. Whilst most galaxies are thought to host a supermassive black hole, only a small percentage of them are this luminous and fewer still go one step further and form what are known as relativistic jets. The team studied a large selection of galaxies with extremely luminous centres – known as active galactic nuclei (AGNs) – thought to be the result of large quantities of heated matter circling around and being consumed by a supermassive black hole. Calçada (ESO)Ī team of astronomers using the NASA/ESA Hubble Space Telescope's Wide Field Camera 3 (WFC3) have conducted a large survey to investigate the relationship between galaxies that have undergone mergers and the activity of the supermassive black holes at their cores. Artist's illustration of galaxy with jets from a supermassive black hole.
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