## Preparing Paper #2 & GSnap Updates

During the recent AAS meeting in Long Beach, CA, I gave a dissertation talk describing the current state of my project and the planned work. After the talk, Jong-Hak Woo,  and others asked some questions that motivated me to perform a bit more analysis. Over the next few days, I added several new features to GSnap in order to answer these questions quantitatively. In summary:
1) What is the probability of measuring $$\sigma_{*}$$ above a given value when the two nuclei pass through one another?

In order to investigate this, I wrote a histogram routine that allows me to plot the probability of measuring $$\sigma_{*}$$ in several velocity bins. In the upcoming paper,  I will present the probability distribution data computed by measuring $$\sigma_{*}$$ along 10,000 random directions.
2) How does $$\sigma_{*}$$ vary with viewing direction (i.e., viewing angle)?

I added the ability to measure velocity dispersion along any specific direction. This allowed GSnap to be scripted so that $$\sigma_{*}$$ can be plotted as a function of the polar angle and azimuthal angle.
3) Measurements of velocity dispersion include both streaming, bulk flow motion and true velocity dispersion; how significant is the contribution of the streaming motion in the measurements of velocity dispersion shown my time series plots?

I derived an expression for the apparent velocity dispersion in terms of intrinsic velocity dispersion, relative mass, and relative (streaming) velocity. This allows me to separate the streaming and random components of the motion in special cases.

In addition to adding more velocity dispersion analysis features, many other new features have been added to GSnap. Most significantly:

• The pixel brightness scaling curve is now more complicated than a simple gamma correction. This results in a much smother transition to black and therefore fewer ragged edges in the images (see images below).
• Renderings of the gas component are no longer monochromatic. The user can specify an arbitrary color map. If a gradient is used for the color map, warm and cool gas can be distinguished from their colors (see images below).
• A basic scripting language has been defined. GSnap can now read scripts and perform automated tasks while loading the snapshot file only once. Previously, the snapshot needed to be re-loaded for each different task.

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