Galaxy Surveys
Galaxy Surveys
Goals: Understand the extragalactic data from Earth's perspective; begin exploring the 2dF and Sloan galaxies.
Before starting, turn on: galaxy, stars, constel, mwVis, galac
You will be using: 2dFgals, SloanGals, 1Gly, 20Gly
If you're continuing from a previous tutorial, quit Partiview and restart the Extragalactic Atlas for a fresh start. Once the Atlas appears, turn off the local group. You should be left with the Point of Interest marker. Fly toward it until it disappears. Now you should see nothing.
We're first going to look at these surveys from Earth. Turn on the stars, constel, mwVis, and the galac groups so that you see the stars, constellations, the visible all-sky image, and Galactic coordinates for reference.
Viewing Galaxy Surveys from Earth
Turn on the 2dF galaxies. As you pan around the sky, you will see one strip of yellow toward the northern Galactic latitudes and another strip surrounded by dots in the south Galactic polar region. Each of these dots of galaxies shows the actual telescope footprint on the sky. If you look at each closely, you will see they are 2 degrees wide and contain many galaxies.
Now turn on the SloanGals group to see the Sloan galaxies. You will see more coverage on the sky, particularly in the northern Galactic hemisphere. These are two major galaxy surveys that astronomers have completed. As you can see, they cover only a portion of the entire sky, often in narrow strips.
Now turn off the Sloan galaxies so that you're left with only the 2dF survey. Position yourself so you're looking toward the random fields (dots) in the south Galactic pole. Begin flying away and, as you do, notice the random fields appear to be pulled in toward the Milky Way. You may also notice that the stars, Milky Way all-sky, constellations, and coordinates all lie on a fixed sphere. Because the distance to the stars would be extremely small on this scale (megaparsec), we placed the stars and related data groups on a fixed sphere with a radius of 1 megaparsec (1 million parsecs).
Flying Away from Earth
As you pull back, you'll be out of the data set in no time. Once you see most of the galaxies, stop and orbit.
From out here, you can see the large-scale structure of the Universe: dense clusters of galaxies connected by strands of galaxies, and areas where there are fewer galaxies, called voids. Turn on the 1 billion-light-year grid and the 20 billion-light-year grid to see the scale of these galaxies. The random pointings now appear as pencil beams that extend out billions of light-years from the Milky Way.
The bow-tie shape of these data indicates the patches of sky that were surveyed. Imagine if the entire sky were surveyed, you would see similar data surrounding the Milky Way in a spherical distribution. The Sloan Digital Sky Survey's original goals were to do just that. Let's turn the SloanGals back on and see them in 3-D.
You may want to adjust their brightness using the Slum Slider. The Sloan galaxies also show the large-scale structure, that pattern of clusters, filaments, and voids. This is the structure of the local Universe. Remember, for a galaxy 3 billion light-years away, the light traveled for about 3 billion years to reach the lens of the observing telescope. Does the evolution of the Universe affect this view? How far do you have to look before the large-scale structure you see currently is nonexistent or is in an unrecognizable phase?
We will continue exploring these questions in subsequent tutorials. For this scale, we are still looking at objects generally in the same cosmic era. Yes, when we look at a galaxy 3 billion light-years away, we're seeing it as it was 3 billion years ago. However, this is a relatively short time, cosmically. Next we'll discuss quasars, objects that we see only at great distances.
© 2002-2005 American Museum of Natural History
Last Modified: 2007-12-19 by Brian Abbott