I was attempting to make catalog for one of the Frontier-fields cluster. But I realized some faint objects are not in my catalog.

I checked Segmentation map and realized this object did not consider as true clump, while, the fainter objects considered as a clump.

I expected the S/N of main object (which did not consider as a clump) became smaller the S/N threshold and S/N of faint objects (which considered as clump) was larger than S/N threshold. While S/N of both of them were smaller than the S/N threshold.

But why the fainter objects considered as clump, they should be ignored because the S/N of these objects were smaller than S/N threshold. I think this is a bug and it should be solved.

For producing this problem I put all the command use for making this segment below.

At first, I downloaded a frontier-fields cluster by below command:

wget https://archive.stsci.edu/pub/hlsp/frontier/abell2744/images/hst/v1.0/hlsp_frontier_hst_wfc3-60mas_abell2744_f160w_v1.0_drz.fits
-Oabell2744-f160w.fits

Secondly, based on the below command I crop the deeper part:

astcrop abell2744-f160w.fits -h0 --polygon="3.6034055,-30.4165889:3.5655321,-30.4135259:3.5722988,-30.3765434:3.6103451,-30.3816284" --mode=wcs --output=crop.fits

Then I run NiseChisel on output of the astcrop:

astnoisechisel crop.fits --output=nc.fits

Finally, I have make a flat(3*3) kernel and based on this kernel Segment was built.

astconvert flat.txt --output=kernel.fits
astsegment nc.fits --kernel=kernel.fits --snquant=0.99 --gthresh=1000 --grownclumps --output=seg.fits