A study of 29 bright quasars has turned up something unexpected. Four of these quasars are located inside dusty galaxies that are still rapidly forming stars, but the quasars are so powerful, they may be punching holes in the galaxy, allowing us to see them. The discovery could help explain giant galaxies where little stellar formation has occurred for billions of years.
Peering back towards the dawn of time, astronomers see giant galaxies that are so busy making new stars, they are called dusty starburst galaxies, with the dust a byproduct of star formation and explosion. Yet when we look closer to home, many equally large galaxies have become burnt out, barely able to produce new stars. This creates a puzzle as to the reason for the transformation.
Astronomers have detected some distant starburst galaxies that, considering their enormous distances, are bright at wavelengths somewhat shorter than a millimeter. Surprisingly, many of these galaxies have been found to lie close to quasars – supermassive black holes accreting material so rapidly they emit vast amounts of energy. Indeed, about a third of quasars at distances greater than 12 billion light-years appear to be in close proximity to these “submillimeter-bright galaxies” (SMGs).
To investigate this relationship, the Atacama Large Millimeter/submillimeter Array examined 29 quasars. In 16 cases, the quasar and SMG are close but not co-located, possibly engaged in a gravitational dance. The authors of the paper in the Astrophysical Journal believe the quasar’s light will be useful to probe the circumgalactic medium around the SMGs.
Four of the cases are even more interesting, with the quasars apparently located inside the dusty starburst galaxies. This was unexpected since such thick dust ought to obscure the quasars. "So, the fact that we saw any such quasars implies that there must be more quasars hidden in dusty starbursts," said Dr Hai Fu of the University of Iowa in a statement. "To push this to the extreme, maybe every dusty starburst galaxy hosts a quasar and we just cannot see the quasars."
So why are these quasars visible? Fu and his co-authors propose that the quasars are emitting so much energy that they pushed out enough gas and dust to convert the galaxies into doughnut shapes. We can see these particular quasars because the galaxies happen to be aligned with their holes facing us. With so much raw material expelled from the galaxy, star formation stops, eventually leading to the galactic wastelands we see today.
The study also found two quasars that are close to, but not inside, galaxies with which they may be merging. These two quasars could prove extremely interesting targets for future study, potentially giving us unprecedented information about galactic evolution and the material that surrounds large galaxies.
