Thursday, May 24, 2012

First Look at the Data

The first thing I've done today is figure out how to make a general SQL query into the SDSS3 database so I can extract various pieces of information.  My main goal for today was to create a number of color-color diagrams.

So here is the first one.  It's a plot of U-R along the y-axis, and R-Z along the x-axis.  As you recall, Z, R, and U correspond to the stellar magnitude (brightness) of a particular object taken with (in this case) three different color filters.  I've explained the color filters in this blog entry, so I won't go into detail here.

Here is the plot:

Color-Color Diagram R-Z vs U-R (3425 "stars")
Each tiny point on this plot corresponds to a "star" that was detected and cataloged by the SDSS3 pipeline processor.

Here is the corresponding plot showing all detected "galaxies":
Color-Color Diagram R-Z vs U-R (6041 "galaxies")
The first two things that catch my eye is the shape of  the distributions, and all those points that are way outside the main distributions.  The shape will tell me something (TBD) about the population of stars/galaxies I'm working with.  The outlyers, as they're called using the jargon, need to be looked at to see why they're so far out of the norm.  It could be lots of things but most likely I think what I'm going to find is that there was some kind of error in measurement.  But they could also be very interesting stars/galaxies and worth taking a very hard look at.

The other interesting thing I'm seeing at first glace, especially in the stars plot, is the various areas where there seems to be more densely packed stars.  What's that all about?  Further analysis will tell me.

And yes, I'm revising the object count in this project.  There are 3425 detected "stars" and 6041 detected "galaxies".  I'm putting those words in quotes because it's a fact that there will be some (maybe many) false identifications that I'll have to work out. Wow -- that's 9467 objects in this very tiny 1/16th of a square degree field!

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