Changes between Version 7 and Version 8 of Background_Oversubtraction

Timestamp:

Mar 8, 2011, 5:15:44 PM (15 years ago)

Author:

eugene

Comment:

--

Background_Oversubtraction

@@ -33 +33 @@
 The above 2 images show portions of another exposure, this time of MD04.  Again, the red boxes mark all detections, while the blue boxes show the 'good' objects after filtering.  
 
+Summary: this additional filter can remove insignificant and otherwise uninteresting detections coming from low-level variations in the background flux.  
 
+One concern with this filter is that it (intentionally) rejects objects which are extended and have low surface brightness.  Although most galaxies will continue to be accepted, this filter will necessarily increase the rejection fraction of low-surface brightness galaxies.  After all, they have an appearance very similar to the artifacts causing the excess detections. 
+
+There are 2 points to be made regarding the detection of real, low-surface brightness features:
+
+1) such detections should be performed on the stacks, where the non-astronomical background variations should be reduced due to the stacking.  We should be able to relax the Core / Kron rejection threshold in such an analysis.
+
+2) The detection of extended, low-surface brightness features should be performed with an additional analysis step that is not the same as a PSF-optimized search.  For example, the analysis should smooth the image with a kernel larger than the PSF (to enhance faint extended features).  In addition, the 'footprint' analysis, in which detections are grouped together, should be performed on the smoothed image to avoid splitting up the extended low-surface brightness structures.  In this case, although we will still be sensitive to errors in the background, we will not generated dozens of detections but only a small number for each such feature.  
+