Wednesday, July 29, 2009

Willman I Gradient

I've spent the last two weeks messing around with finding the best fit slope for Willman I's velocity distribution along its major axis.

The best fit has a slope of -.484 km/s/arcminute.

But I wanted to figure out how likely this is, so ran a couple of simulations. Based on Willman I's mean velocity, position, and spread in spatial points, I simulated 100,000 fake galaxies with specified velocity dispersions.

With a velocity dispersion of 1 km/s, an absolute slope of greater than .484 is never (or almost never) found.

A velocity dispersion of 5 km/s has a slope higher than that value 17.01% of the time and a velocity dispersion of 10km/s has a greater slope 48.75% of the time.

The velocity dispersion of Willman I is 3.52, and just for kicks, the probability of it having that slope with that dispersion is 5.40%.

1 comment:

  1. Nice results.

    Have you made pretty figures to present the results in detail? How did you end up simulating the measurement errors?

    I'd also be interested to know the reduced chi2 values of the best fit lines... for example when lines with slope are found as the best fit - what are the associated best chi2.

    When calculating what fraction of the time slopes "greater than" the value of 0.484 are found... did you take the absolute value of the derived slope?

    Don't forget to write your paragraph for Suzanne.