By studying a sample of distant galaxies, whose light reaches us from a cosmic epoch when the Universe was just three billion years old, a team of researchers led by Giustina Vietri of the Italian National Institute for Astrophysics (INAF) has followed the winds blowing in “active” galaxies down to only a few light-years from the supermassive black holes that sit in the galactic cores. The new study demonstrates how these winds, which travel as fast as millions of kilometres per hour, have the potential to influence interstellar gas on scales of tens of thousands light-years.

The majority of supermassive black holes lurking in galaxies, like the one at the centre of our own Milky Way, are harmless and swallow at most the occasional star or gas cloud that dare venture too close. A small percentage, however, is in great turmoil, devouring the surrounding matter at high pace via an accretion disc that heats up and emits radiation across the electromagnetic spectrum. It is from these signals that it is possible to recognise “active” galaxies, hosting such frenzied black holes, in astronomical observations.

Not even the most “voracious” black holes, however, are capable of eating all the material in their surroundings, triggering enormous winds that throw away part of this material and can propagate over galactic scales. Astrophysicists have been debating for years about the importance of such winds and their possible effects on the evolution of the host galaxies via feedback mechanisms, which might have the potential to regulate both the growth of the central black hole and the formation of new stars.

“It’s a topic of great importance to understand how the Universe has evolved”, comments Giustina Vietri from INAF in Milan, first author of a new study analysing the effect of such winds on different scales within galaxies, for the first time using a representative sample of active galaxies. “In this study we tried to shed new light on one of the currently most debated issues: the link between the central supermassive black holes and their host galaxies”.

The results, published in Astronomy & Astrophysics, are part of the SUPER project (A SINFONI Survey for Unveiling the Physics and Effect of Radiative feedback), which has already produced two papers authored by the same team of researchers. The project was created with the aim of studying the release of gas from galactic centres using the SINFONI instrument on ESO’s Very Large Telescope, in Chile.

“SINFONI is an integral-field spectrograph operating in the near-infrared and exploiting adaptive optics to gather high-resolution spectra of extended sources”, explains Vincenzo Mainieri from ESO, principal investigator of the SUPER project and co-author of the new study. “With respect to previous instruments used for spectroscopic surveys of active galaxies, SINFONI enables us to spatially resolve the gas”.

Thanks to the data obtained with SINFONI, the team has analysed a representative sample of 21 active galaxies, studying the connection between black holes and their host galaxies, for the first time, in a systematic fashion. This means they did not have to select galaxies where the presence of winds was already known. The observations have revealed the presence of galactic winds in all examined sources. The result demonstrates how prevalent these phenomena are in the cosmic epoch to which these galaxies belong, when our 13.8 billion-year old Universe was only 3 billion years of age.

“These winds, travelling at speeds between 3 and 7 million km/h, reach out to twenty thousand light-years from the centre of their host galaxies”, adds co-author Michele Perna from INAF in Florence and Centro de Astrobiología in Madrid, Spain.

The researchers then followed the winds all the way to their origin, in the vicinity of the monster black holes, by making use of an astronomical “microscope” – analysing optical spectra of these galaxies available from the archives.

“The lines emitted by ionised carbon atoms, which we see in spectra from the Sloan Digital Sky Survey, are produced only a few light-years away from the black hole, revealing how the winds of ionised material discovered with SINFONI are also present on these relatively small scales, in the heart of galaxies”, explains Vietri. “By doing so, we could link for the first time the presence of outflows from the proximity of the black hole to galaxy scales”.

The results show how the winds observed at small distances from the central black hole depend on its properties – such as the accretion rate or the brightness of the galactic core, which is in turn produced by the black hole’s activity. Furthermore, these winds might have the potential to influence gas all the way to the outskirts of their host galaxies. In the future, the researchers will try to trace these winds on even larger scales to keep studying the influence that black holes may exert on the evolution of galaxies.

The study is published in Astronomy & Astrophysics in the paper “SUPER III. Broad Line Region properties of AGN at z∼2” by G. Vietri, V. Mainieri, D. Kakkad, H. Netzer, M. Perna, C. Circosta, C. M. Harrison, L. Zappacosta, B. Husemann, P. Padovani, M. Bischetti, A. Bongiorno, M. Brusa, S. Carniani, C. Cicone, A. Comastri, G. Cresci, C. Feruglio, F. Fiore, G. Lanzuisi, F. Mannucci, A. Marconi, E. Piconcelli, A. Puglisi, M. Salvato, M. Schramm, A. Schulze, J. Scholtz, C. Vignali, G. Zamorani

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