2dF Quasar Survey
Two-degree Field Quasar Survey
| Group Name | 2dFQSOs |
| Reference | The 2dF QSO Redshift Survey (Colless+ 2003) |
| Prepared by | Eric Gawiser (Rutgers University) |
| Labels | No |
| Files | 2dfqsos.speck |
| Dependencies | none |
| Census | 22,431 quasars |
If you are familiar with the Two-degree Field (2dF) galaxy survey, you may know that the 2dF also surveyed quasars, the farthest objects in the Universe. For details on the 2dF survey and instrument, please see “Two-degree Field Galaxy Survey.” The data variables associated with the 2dF quasars are the same as those in the 2dF galaxies.
Discovering Quasars
Radio astronomy was born in 1931, when Karl Jansky of Bell Telephone Laboratories discovered that the Milky Way was radiating its own radio waves. In the years following World War II, hundreds of radio observations were recorded and cataloged in the Third Cambridge (3C) Catalog of radio sources. Many of these sources were identified to have a nebulous optical counterpart, like the Crab Nebula or the nearby galaxy Centaurus A.
However, in 1960, astronomers detected the first object that radiated radio light but appeared like a faint blue star rather than a nebulous cloud. This object, 3C 48, was mysterious because its spectra revealed lines that were unfamiliar. Astronomers thought they had discovered a new class of radio-emitting stars.
About two years later, this object was joined by another, 3C 273. Astronomers observed the same spectral features in this object, and in 1963, Maarten Schmidt of Mount Wilson Observatory discovered that these were not new lines but were the familiar hydrogen lines shifted by 16% into the radio spectrum. This redshift (0.16) was the largest that had been observed to date and meant that the object was receding from us at about 16% the speed of light.
With such large redshifts, these objects were clearly not stars in our Galaxy. Furthermore, their enormous distances implied that they must be incredibly bright. In fact, they are the brightest objects in our Universe, comparable in luminosity to 20 trillion Suns or 1,000 Milky Way Galaxies. But what are these mysterious objects?
What Are Quasars?
Quasars have been observed in all regions of the electromagnetic spectrum, but they emit most of their light in the infrared. They resemble active galaxies but have much higher luminosities. An active galaxy has a supermassive black hole at its center that gobbles up gas from a surrounding accretion disk. This process emits high-energy light that can be seen to great distances. Quasars are simply more intense versions of these active galaxies. The central black hole consumes more material over the same period.
Quasars are our baby pictures of the “normal” galaxies we see nearby. The look-back times for the 2dF quasars range from 1 billion to more than 11 billion years. Consider a quasar with an 11 billion-year look-back time. The light we see from that quasar left 11 billion years ago, when the Universe was very young. By now, the quasar has no doubt evolved into something else, perhaps a calmer galaxy.
Astronomers believe that quasars are snapshots from the formation stage of galaxies. As a galaxy comes together, it is very active and unsettled. This is the quasar stage. As the object evolves, its black hole consumes material left over from the galaxy's formation and that rate of consumption slows over time. This is the active, or radio, galaxy phase. Once there is a lack of material for the black hole to feed on, the galaxy becomes less active and enters its normal stage, like our Milky Way. The Milky Way still has a massive black hole at its center, but its rate of consumption has slowed to the point where the energy emitted is much less than that of an active galaxy.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott