Point Source Extraction in the Extragalactic First Look Survey:
MIPS-SCAN, band 1, 24 micron

Requirements:

Follow the instructions on Imaging: Point Source Extraction

Outline of the demo:

This demos demonstrates how to select point sources for PRF estimation, run the PRF estimate tool, and then use the real PRF for point source extraction. Special care is taken in removing Airy rings of bright point sources as they create false detections. The final products are a table of point source fluxes and a point source subtracted mosaic image.

You will need to run these scripts:

prf_estimate.pl
apex_1frame.pl
apex_qa.pl

You will need to use these namelists:

Step by Step Guide

The first step consists of extracting sources from the mosaic image that will be use to estimate the PRF:
unix% apex_1frame.pl -n apex_1frame_step1.nl
Use the PSP image to detect (set use_psp_to_detect = 1) and set the detection threshold to a large value to only include high SNR point sources (Detection_Threshold = 20). Use the MIPS-24 PRF found in the cal/ directory of the MOPEX package.
The table of extracted sources is apex_1frame_step1/mosaic_extract.tbl.

Select the brightest point sources with the best fit:

unix% cd apex_1frame_step1
unix% select col all from mosaic_extract.tbl for "deblend = N and chi2/dof < 30 and flux > 5000" into mosaic_extract_clean.tbl with header

The new table of extracted sources is mosaic_extract_clean.tbl.

Visualize which sources you will use for PRF estimate with your favorite image viewer.
If using skyview, you can do:

unix% cd ..
unix% skyview
> pa data/main/mosaic.fits
> table apex_1frame_step1/mosaic_extract_clean.tbl mark $RA $Dec circle red 1

Run PRF estimate with the input point source list mosaic_extract_clean.tbl:
unix% prf_estimate.pl -n prf_estimate.nl
Set the size of the PRF postage stamp image (PostStamp_Xsize = 35, PostStamp_Ysize = 35) and the sampling factor (PRF_ResampleX_Factor = 4, PRF_ResampleY_Factor = 4). If the PRF fluctuates a lot at the edge of the postage stamp image, set a region around the edge to zero (for an edge measuring 5 original pixels, set Zero_Edge = 5).

Copy the new PRF image to the cal directory:

unix% cp prf_estimate/PRF.fits cal/PRF_estimate.fits

The Airy rings of the bright point sources create false detections. To remove the first (and brightest) ring, run:
unix% apex_1frame.pl -n apex_1frame_noring.nl
Use the PSP image to detect (set use_psp_to_detect = 1) and set the detection threshold to a large value to only include bright sources (Detection_Threshold = 20). Use the new PRF image. Set the detection threshold type to 'combo' (Threshold_Type = 'combo').
Create ring subtracted image:
unix% apex_qa.pl -n apex_qa_noring.nl
Do not subtract the circular region of the PSF within the first minimum (HoleRadius = 21). This means that only the first Airy ring and beyond will be subtracted from the image. Set the radius for PRF subtraction (Radius = 44).
Run detect on the ringless image:
unix% apex_1frame.pl -n apex_1frame_step2a.nl
Run the modules run_medfilter, run_gaussnoise, run_pointsourceprob, and run_detect (set them all = 1). Do not run the run_sourcestimate module at this point (set run_sourcestimate = 0). Use the PSP image to detect (set use_psp_to_detect = 1) and set the detection threshold to a low value (Detection_Threshold = 5).

Copy files to correct names for flux estimation (next step):

unix% cd apex_1frame_step2
unix% cp residual_mosaictrim_detect.tbl mosaictrim_detect.tbl
unix% cp residual_mosaictrim_minus_median.fits mosaictrim_minus_median.fits
unix% cp residual_mosaictrim_noise.fits mosaictrim_noise.fits
unix% cp residual_mosaictrim_PSP.fits mosaictrim_PSP.fits

Run flux estimation using the original image:
unix% cd .. unix% apex_1frame.pl -n apex_1frame_step2b.nl
Use the new PRF image for flux estimation. Select the fitting area (Fitting_Area_X = 9, Fitting_Area_Y = 9) and the active deblending parameters (Max_Number_PS = 3, Chi_Threshold = 10). Set the normalization radius for aperture correction (Normalization_Radius = 44).
Produce point source subtracted image:
unix% apex_qa.pl -n apex_qa.nl
Apply aperture correction