Closed esheldon closed 4 years ago
bias goes away with gauss psf
ah - we have to stack enough PS PSFs to reduce the PSF variation
how many epochs?
3 is too few IIUIC
we already tested this before, so this is a regression
note variation_factor: 1.0
Are you sure?
The only difference was that the other test used brighter objects.
Here is the old result with the ~17.5 mag exp gals
5.46647e-05 +/- 0.000511308 (3 sigma)
New results mag=22 objects (still high s/n)
0.0012705 < m1 < 0.00178272 (99.7%)
Does the new code work with brighter objects?
not to mention, we tested PS psf with full wldeblend galaxies and it worked perfectly
Well I'll be damned, it did work for the brighter objects
0.000262936 < m1 < 0.000404232 (99.7%)
Wow
I had run the brighter one with wider grid spacing. Running the faint one with wider grid spacing also works
-4.08625e-05 < m1 < 0.00044735 (99.7%)
wider is 6x6 grid rather than 8x8 grid
Well, I decided to burn some time verifying this is OK with random placement of the galaxies, and it looks ok
0.000151968 < m1 < 0.000755387 (99.7%)
so I think the bias for the close packed grid was in fact due to the close spacing, such that every single object was blended and the blending was of a similar degree and character in most of the cases (different near the edge of the grid)
I can't say I really understand it, but I don't see how it could affect a realistic scenario.
I ran with small galaxies, hlr=0.1, mag 17.5 on a 6x6 grid and did get some bias.
0.000441331 < m1 < 0.000957044 (99.7%)
So this I think connects back to the bias we were seeing in the gals+stars run with PS/moffat psf. There are a lot of small galaxies in the wldeblend sims. Seems to be an issue of moffat + small galaxies. There may be some additional bias due to having stars.
My intuitioin is that the bias is from deconvolutions/reconvolutions with the moffat. I do see artifacts for very bright stars with the moffat PSF and psf stamp size of 53x53, but I had hoped it was only a problem if there were really bright stars in the image. But I think it bites us for small galaxies too
So fitgauss is too aggressive and needs to widen the PSF a bit more?
Maybe.
I see the artifacts for psf: gauss
too...
If I run with variation_factor: 0.001
the bias goes away
So I think your guess might be correct, that we need more epochs.
which test? the original one?
I ran the test with mag 17.75, hlr 0.1 but with variation_factor 0.001 rather than 1
the bias for variation_factor 1 I got
0.000441331 < m1 < 0.000957044 (99.7%)
with variation_factor 0.001 I got
-4.69865e-05 < m1 < 0.000262134 (99.7%)
Running with 3 epochs and variation factor 1
2.17194e-05 < m1 < 0.000422611 (99.7%)
Great! I'd say this is solved?
I think so.
It was wrong to call it a regression; I don't think we specifically tested some of these scenarios before
No worries!
Is it possible to mock up the effect of 3 epochs by modifying the variation_factor?
OFC, but IDK how to calibrate that except to do actual sims
This PS PSF "model" is VERY crude. It is a way to generate variation quickly. I cannot promise it relates to other things much more than this.
Before we do any more runs with PS psf I think we'll need to calibrate this some how.
Yup. And we should figure out if the correlation structure is right. I built that to show that in principle PSF variation can be averaged down.
This sim is now giving 0.15% bias