Quasar Surveys
Quasar Surveys
Goals: Explore the characteristics of the quasar surveys.
Before starting, turn on: 2dFgals
You will be using: 2dFQSOs, SloanQSOs, 20Gly, alpha command
As we look farther out into space, we are looking further back in time. Quasars are the farthest objects we see. The nearest quasar is 1 billion light-years, but most are more than 10 billion light-years away. Reflecting a greater abundance at an earlier time in the Universe, quasars provide evidence that we live in an evolving Universe where objects change over time.
What Is a Quasar?
Quasars are violent, extremely luminous galaxies. There are many types of active galaxies (Seyfert galaxies and radio galaxies for two), but quasars trump them all in power and brightness. The light we see from a quasar is from synchrotron radiation and occurs from electrons moving close to the speed of light in a strong magnetic field.
Quasar Distribution
Let's look at some quasars in the Atlas. Begin from a vantage point where you see all the 2dF galaxies. If you're continuing from the previous tutorial, then you should be set if group 2dFgals is on.
As we mentioned in the previous tutorial, the 2dF galaxies extend to about 3 billion light-years and the bow-tie shape of these data reflects those parts of the sky that were observed by the telescope.
Now turn on the 2dF quasars. As you can see, they appear like a natural extension to the galaxies. Nearby, there seems to be less density and the number of quasars increases as the distance increases toward their average distance of 13.4 billion light-years. By about 15 billion to 20 billion light-years, the density of quasars begins to fall off. This fall-off is due to the limiting magnitude of the telescopes—their cut-off is set by brightness, typically around 20th magnitude—and objects dimmer than this will not be detected.
Turn off the 2dF quasars and turn on the Sloan quasars. If you turn on the 20 billion-light-year grid, you can see that these quasars have the same properties as those in 2dF. If you want to see the grid throughout the data, you can make it completely opaque by increasing its alpha value to 1. We like the grids semitransparent, though, so they don't dominate the scene.
While quasars are the farthest objects we can see, there is light from an earlier epoch that pervades the Universe, called the cosmic microwave background. We will discuss this light in the next tutorial.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott