Monday, July 19, 2010

Likelihood (again)

Here is the final push to get the likelihood algorithm finalized for the rest of the survey....

Where we last left off, I had been trying to optimize the QSO Catalog, but had been setting the thresholds wrong. Once I fixed that, I tried again, and realized that something was going wrong with my attempts to change the inputs to the QSO Monte Carlo, such that it was failing. So now let's try again.

First step, reproduce old likehood results (v1):

saved in the files:

The field l_ratio is computed the following way:
eps = 1e-30
bossqsolike = total(likelihood.L_QSO_Z[2:18],1) ;quasars between redshift 2.1 and 3.5
qsolcut = where(alog10(bossqsolike) LT -9.0)
den = total(targets.L_EVERYTHING_ARRAY[0:4],1) + total(likelihood.L_QSO_Z[0:18],1) + eps
num = bossqsolike + eps
NEWRATIO = num/den
NEWRATIO[qsolcut] = 0 ; eliminate objects with low L_QSO value
likelihood.l_ratio = newratio

Here is the distribution of the likelihood ratios of v1 (white) and new (green) of the data used to set the thresholds:

Comparing the thresholds I find for v1 compared with Myers' they are within 10% of each other:

Targets/dec^2------My threshold----Myers Threshold

Now comparing v1 of the likelihood with a catalog with the same luminosity function and inputs, but a larger redshift range, we get the following results:

Targets/dec^2------v1 threshold----new threshold

Targets/dec^2--# Targeted QSOs:----v1----new version

Here is the distribution of the likelihood ratios of v1 (white) and new (green) of the quasars:

This doesn't improve things much, and performs worst at 20 targets per square degree (core). It might be because the statistics are now smaller in the BOSS redshift range (I kept the simulation at 10M objects, but now it is distributed over a larger redshift range).

If you look at color-color plots of what was targeted by both version (white), with version 1 (cyan) versus the new version (magenta):

The redshift distribution shows that the new method is finding some higher redshift QSOs however:

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