Playing with Galaxies


Let's kick off the Digital Universe blog with some tips on manipulating data in Partiview. I am the first to admit that Partiview's user interface, while extremely powerful, is not the simplest UI to use. However, if you invest a little time, you can learn some sophisticated moves that will impress your friends.

Two-Mass Galaxy Catalog. Left: the view toward Fornax when you start the Digital Universe, with 85% of the galaxies removed from view. Right: the view with the full catalog in view. Most of these are blue, field galaxies which are not part of a galaxy cluster.

Brian Abbott/AMNH

I will focus today's post on the recently added 2MASS Galaxy Catalog. The catalog is wonderful for showing the enormous number of galaxies around the Milky Way. There are 1.14 million in this catalog (still, just the tip of the iceberg), but we do not show them all when you start up the Extragalactic Atlas. In fact, we only display 15% of the galaxies by default; your screen would be nothing more than a plethora of points if the full set was displayed.

Oh, you want to see that? Well, fire up the extragalactic data and turn on the 2MASS Galaxies.

Before we dive in, check out the data and preset selections available to you. In the 2MASS Galaxy Catalog section in the DU Guide, look over the tables that describe the data available, extra data associated with each galaxy, and the selection expressions that allow you to cull portions of these data.

We can use these expressions to selectively see different parts of these data if we learn how to use the command line (the gray box beside the "Cmd"). Using the Partiview command see, type see all to reveal all 1.1 million galaxies. Pretty crowded, huh?

Nearby Galaxy Clusters

Looking back to the Milky Way from 570 million light-years away. The surrounding nearby clusters are apparent once you use the clusters selection expression.

Brian Abbott/AMNH

Luckily, I have added some selection expressions to make it easy to manipulate these data. To return to the default state with 85% of the galaxies removed, type see lss. By removing the more isolated field galaxies in blue, the large-scale structure (hence, lss) is easier to see.

If you want to have a sense of the galaxy clusters that surround us, type see clusters at the command line and orbit Home. Our nearest neighbors are the Fornax Cluster, in the direction of Fornax in the sky, and the Virgo Cluster, the large, galaxy-rich cluster in the constellation of Virgo. Each of these clusters is a goldmine for astrophysicists, providing invaluable knowledge toward our understanding of galaxy clusters and superclusters.

Try some of the other 2MASS selection expressions to learn more about the galaxies that surround us. Next time, I'll discuss the various catalogs that make up the 2MASS Galaxies.