It's All Coming Together!

I figured that it was probably time for me to talk about my research project again, and I actually have something to say today! So that's good timing.

Remember that code I was working on for all of last week?  Crushed it!! But I have to say that my greatest accomplishment of the week is finally putting all of the puzzle pieces together and seeing the big picture that is this project.  And I'm going to share that epiphany with you!

I'm going to start with another description of my project.  I'm determining the physical characteristics of a starburst galaxy--a galaxy that's undergone a lot of intense star formation--in the hopes that we'll be able to use it as a template for high-redshift galaxies.  The problem, though, is that galaxies aren't homogeneous creatures.  They vary in density, temperature, and composition throughout.   And that's great and all, but it's really annoying to model.

I'm particularly interested in the variances that come from two different regions of the galaxy--HII regions and PDRs.  HII regions are clumps of ionized hydrogen gas that occur when new stars are formed.  PDRs (Photodissociation Regions) are a little bit harder to explain.  Basically, they're regions in the inter-stellar medium (a fancy phrase for the space between stars) where UV light photons knock electrons off of dust grains.

Diagram of a PDR from Hollenbachs's Article on Dense PDRs

I intentionally made my explanation pretty light, so if you have questions, feel free to comment with them, and hopefully I'll be able to answer. 

Okay, now that you know that, on to my epiphany!  Until this week, I was kind of just going with the flow of my various assignments.  Reduce this data.  Identify these lines. Make these plots. And I did it all, faster than  and with more enjoyment than I expected, but I didn't really know why. But now I do, and here it is, step-by-step.  

1) Take this data, reduce it (this, I've learned, is a simple way of saying "take a massive glob of data and cut out all of the useless stuff to get down to the pretty information that will make you happy").  Why did I have to do this? I was looking for the spectral lines that I would then use to actually figure out the characteristics of the galaxy.  Pretty simple, actually.  

2) Take the newly reduced data and compare it to the models created by a scientist named Rubin.  Why?  Well, apparently, Rubin was modeling the HII regions with different parameters (density, temperature, composition, etc.) and recorded the intensities of different lines that for each individual model.  I compared my data to his to see which model of an HII region most accurately represented the data I had.  

3) Take the intensity values for each line and enter them into an online program that spits out contour maps of the PDRs.  I did this to model the PDRs...not too hard to understand in the grand scheme of things.

4) Use a program called CLOUDY (I will probably write a post in the near future about how much I hate this program) which is usually used to model nebulas.  It turns out that CLOUDY can also be used to model galaxies.  And since we don't know how much of each line's intensity comes from HII regions and how much comes from PDRs, we're using CLOUDY to (basically) figure out the how the galaxy is divided between the two.  

And that's it. Looking back now, I realize that it probably shouldn't have been to hard to see, but that's hindsight bias for you.  I guess the important bit is that I know why I did this stuff now.