It's been a while, but I've basically been doing the same things or variants on them.

I made a bunch of sweet figures of simulated data and its kurtosis, skewness, and Nmix results. I then plotted real data to see if they matched up at all, which wasn't really the case. But they're still potentially useful figures.

The main problem was that my simulations show that kurtosis is rather strongly negative for simulated Gaussians with small numbers of stars. But most of our data sets have small numbers of stars, so a negative kurtosis won't really tell us anything.

Also, I randomly discovered that running Nmix on the Segue I data set with and without the 5 outlier points yields drastically different results. With the points, the probability of a single component is close to 70%, without them it is only 4%. Something is clearly wrong with Nmix.

But now I'm trying to determine if there are "streaming motions" in the Willman I kinematics, which basically mean rotation. I'll divide the data into chunks based on position and then calculate the average velocity, seeing if some are negative or positive which would indicate spinning. I'm not really sure what that would mean, but since it's not a spiral galaxy, it would probably mean definite tidal disruption.

Well that's all for now and hopefully I'll keep up the blogging.

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Good that you've started the analysis to look for streaming motions etc. Be sure to write your code as generall as possible - so that when you have a different set of data with a different center and position angle and size, that you can easily re-do the calculation.

ReplyDeleteAlso - the loop isn't closed yet on the other stuff... more thoughtful interpretation must be done!