Quasar Radiation Influences Galaxy Growth
July 25, 2013

Quasars Have A ‘Profound Effect’ On Their Galaxies

Lee Rannals for redOrbit.com - Your Universe Online

Astrophysicists writing in The Astrophysical Journal have shed some new light on the universe's brightest objects - quasars.

The team from Dartmouth University published details about discoveries based on 10 quasar observations. They wrote about the power of quasar radiation, which can reach out for many thousands of light years to the limits of the quasar's galaxy.

Astrophysicists Ryan Hickox and Kevin Hainline and colleagues used the Southern African Large Telescope for their observations. This observatory is the largest optical telescope in the southern hemisphere. The team used spectroscopy for the observations, which is when light is broken down into its component wavelength.

"For the first time, we are able to see the actual extent to which these quasars and their black holes can affect their galaxies, and we see that it is limited only by the amount of gas in the galaxy," says Hainline, a Dartmouth postdoctoral research associate. "The radiation excites gas all the way to the margins of the galaxy and stops only when it runs out of gas."

The radiation released by a quasar covers the entire electromagnetic spectrum, illuminating the gas present throughout the galaxy.

"If you take this powerful, bright radiation source in the center of the galaxy and blast the gas with its radiation, it will get excited in just the same way the neon gets excited in neon lamps, producing light," says Hickox, an assistant professor in the Department of Physics and Astronomy at Dartmouth. "The gas will produce very specific frequencies of light that only a quasar can produce. This light functioned as a tracer that we were able to use to follow the gas excited by the black hole out to large distances."

The illumination of gas makes it less able to collapse under its own gravity and form new stars. This means quasars can slow down star formation in the entire galaxy and influence how the galaxy grows and changes over time.

"This is exciting because we know from a number of different independent arguments that these quasars have a profound effect on the galaxies in which they live," Hickox says. "There is a lot of controversy about how they actually influence the galaxy, but now we have one aspect of the interaction that can extend on the scale of the entire galaxy. Nobody had seen this before."