GALWORKS Modifications and Performance

The extended source processor (GALWORKS) has been modified to run optimally with the 2MASS 6X survey scans. The changes and initial performance are given here.

High Level Modifications

• adjust mag thresholds in namelist; the 6X thresholds are adjusted 1 mag fainter in comparison to 1X.

• eliminate NED seedlist

• add XSC seedlist

• eliminate JCAT (bright star) seedlist

• add PSC bright star seedlist

• adjust (tune) bright star masking parameters (effectively increasing the mask radii)

• adjust confusion noise and stellar number density thresholds

• adjust S/N thresholds

• eliminate E/G-score thresholding

• fix 1X bug that (on rare occasions) corrupted isophotal radii

• add photometric analysis and diagnostic tables, comparing 1X and 6X results; file = "log###.gal"

For the most part, mag thresholds are 1 mag fainter for 6X in comparison to 1X. The bright star confusion radii were increased by a factor that was determined using about a couple dozen bright stars from different scans. This 1X to 6X scaling is straight forward and its performance is satisfactory thus far. The XSC seedlist allows not only direct comparison with 1X and 6X photometry, but also supports background removal, and target preference (i.e., the order in which the candidate targets are processed). The PSC seedlist identifies bright stars and necessitates the elimination of the problematic JCAT catalog.

Caveats:

GALWORKS-6X is not modified or tuned to properly process very large galaxies. Since large galaxies are handled by the LGA processing, the 6X pipeline is not necessary. It remains to be seen if the pipe breaks when crossing a Messier object. Likewise, very bright stars (Mag < 0.) may also break the pipe.

Performance

As of April 25, GALWORKS-6X is running in the full 2MAPS-6X pipeline. The pipe will undergo further minor modifications, but is currently (preliminary stages) producing very good results. A few highlights are given below for scan "038" of 010110s.

Background Removal

J-band Coadd Image with extended sources marked in red and bright stars artifacts and masked area marked in blue. The left panel shows the raw image. The middle panel shows the "mask", and the right panel shows the residual (background-removed) image.

J,H, and Ks color version where the left panel shows the raw coadd(s) and the right panel shows the residual (background-removed) coadd(s).

Bright Star Removal -- the horror!

J-band Coadd Image with extended sources marked in red and bright stars artifacts and masked area marked in blue. The left panel shows the raw image. The middle panel shows the "mask", and the right panel shows the residual (background-removed) image.

J,H, and Ks color version where the left panel shows the raw coadd(s) and the right panel shows the residual (background-removed) coadd(s).

Extended Sources The following images show examples of extended sources extracted by GALWORKS-6X. The left panel shows the 3-color, background removed "postage stamp" image. The right panel shows the same image with stars removed. The Ks-band (fiducial) elliptical isophotal radius is shown in blue.

Photometry: 1X vs. 6X

The upper panel shows the J mag results, the next panel the H mag results, the next panel the Ks mag results, and the bottom panel the axis ratio results. Denoted in blue are the (fiducuial) isophotal results and in white are the fixed, radius=7 circular aperture results.

The photometric scatter is ~10% (J < 15th mag), with little if any systematic bias. The elliptical shape (axis ratio) is also consistent between 1X and 6X, with between 5 to 10% scatter. Overall, the results look satisfactory for this scan. The definitive test will include at least an order of magnitude more data points. A combination of many scans should be analyzed.