A remarkable star formation in galaxies with hyper-luminous quasars

Artist's concept of the dusty starburst galaxy WISE J224607.57-052635.0 (Image NASA/JPL-Caltech)
Artist’s concept of the dusty starburst galaxy WISE J224607.57-052635.0 (Image NASA/JPL-Caltech)

An article published in the journal “Astronomy & Astrophysics” describes a research involving 16 of the brightest known quasars. A team of researchers led by the Italian National Institute of Astrophysics (INAF) examined in particular those quasars’ infrared emissions to identify young hot stars in the galaxies hosting them concluding that a lot of them are forming, at a rate up to about 4,000 times higher than in the Milky Way.

The ultra luminous quasars selected for this research emit enormous amount of energy thanks to the supermassive black holes that power them. For these objects it’s normal to have masses millions of times the Sun’s but in this case we’re talking about black holes with masses between 3 and 60 billion times the Sun’s. They’re among the most massive known so far and they have such a powerful gravity that they generate electromagnetic emissions visible at huge distances as the farthest one is about 12.5 billion light-years away.

Due to their nature, quasars can have a significant influence on the galaxies that host them and the possible connection between the formation of a galaxy and the growth of a supermassive black hole has been the subject of heated debates. Various studies showed the risk that a quasar pushes away the interstellar gas that could form new stars and an article recently published describes this phenomenon in dusty starburst galaxies. However, the consequences of quasar activities are not always negative.

The 16 quasars examined in this research were selected from the WISSH (Wise-Sdss Selected Hyper-luminous quasars) catalog, based on the Sdss, 2Mass surveys and data gathered by the Wise and Herschel space telescopes. The infrared emissions from the galaxies that host these quasars are generated by the dust heated by the activity of the supermassive black holes that feed the quasars but also by the young hot stars.

The consequence is that the examination of the infrared emissions from those galaxies allows to estimate the rhythm of star formation within them. In the case of the galaxies studied in this research, it turned out that star formation is really remarkable, as much as the quasars’. The estimate is a rhythm between 1,000 and 4,000 solar masses per year in new stars while in normal galaxies it can reach a few hundred solar masses per year and in the Milky Way it’s one solar mass per year.

Federica Duras of INAF in Rome and Rome Three University, first author of this research, pointed out how these galaxies’ characteristics are out of the ordinary. She hypothesized that the cause is due to extraordinary heating of the dust around the supermassive black hole. These are the perfect objects to study the feedback mechanism created by the influence of the supermassive black hole on the galaxy hosting it. That’s because their activity is extreme and therefore more easily measurable.

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