Intercept-Tests
By Elijah Bernstein-Cooper, July 8, 2015, 0 comments.

We are continuing to test the derived intercept as outlined in the previous post

I performed a test of calculating the likelihoods. The $HI$ cube has 5 channels. Integrating the three channels in the center will recreate a scaled image of the $A_V$ image, minus an intercept. The outer channels will create an image deviating away from a scaled $A_V$ image. The scalar is the dust-to-gas ratio.

The DGR should be 0.5, the intercept 0.9, and the $HI$ width 3. Indeed this is what we find by using the likelihood calculation code for the three parameters. Below are the resulting images.

## $A_V$ model

1. In trying to compare with Lee+12 results I think your test with setting intercept to 0 is the closest to what Lee+12 did (if of course the code is working properly and is handling intercept in the likelihood equation correctly even when set to 0). So, can we trust that $\Delta_V = 12-13$ km/sec is a reliable result that should be compared with Lee+12? How does this compare to your old code you used before trying to include the intercept?
2. I am a bit concerned about this small HI width as in Lee+12 we in section 3 compared N(HI) and $\Delta_V$ with several previous studies and concluded that we agree with previous results - most of these previous studies had $\Delta_V$ almost 2 times larger that what your code is getting.
4. I am also surprised to see that your DGR and $\Delta_V$ become slightly smaller when you set intercept to 0. If there is essentially no background (intercept=0) then at each pixel Av has a higher value than otherwise, meaning that DGRxN(HI) term should be higher. Hmm…. I think more testing is needed, and I would also like to discuss your iterative method (need the updated methods section for this).