GALWORKS Results for Scan 058
-- COMA Core -- Using K-replicated Scans


    Tom Jarrett
    IPAC

    (970324)



This work represents an initial verification of the functionality and design of the 3-channel version of GALWORKS before real 3-channel data has been acquired. The data set consists of K-band scans replicated to generate H and J scans (some simple color corrections are made to mimic better J and H colors of stars). This memo describes some of the key results from faux "3-channel" tests.


SEEING

The following figure shows the seeing for scan 058 corresponding to the night of 95-05-03. The seeing is represented by the "shape" parameter, which is a combination of two parameters describing the stellar profile:
The figure represents shape versus scan coordinate. Two versions are included: The first is the "seeman" version, or the seeing values computed by the SEEMAN module (for additional details see the SEEMAN SDS); The second is the GALWORKS version, "seeridge" which uses the same information as the SEEMAN version but computes the seeing with a slightly more sources per seeing value (and thus is a more accurate measure of the seeing, assuming that the seeing is tracked during the duration of time comprising the set of sources per seeing value).

For good seeing, (FWHM < 2"), the shape value is less than 1.1 or so. Very bad seeing corresponds to shape values > 1.2 or so.



Postage Stamp Images

Below is an example of some output from GALWORKS. Reminder: the J and H images are really K-band images in this data set. The first column is the J band image, second column the H band image, third column the K band image and the fourth column is the DSS optical image. The dark blue elliptical contour represents the 20 mag per sq. arcsec isophotal area, and the light blue contour the "flux growth" elliptical area. Sources that had been "subtracted" from the object fields are circled in red with the size of the circle given by the subtraction radius. Sources circled with a green circle/ellipse represent sources that were previously processed and subsequently blanked from the object field (blanked pixels are then substituted with corresponding isophotal values given by the object of interest, thereby recovering pixel information).



Score Parameters

A number of parameters are used to distinguish stars (point sources) from galaxies (extended sources). There are three basic kinds of parameters to this end: (1) the peak flux versus integrated flux, (2) radial profile, and (3) emission located beyond the central peak and wings of a stellar PSF, and various combinations thereof. The central surface brightness to total brightness parameter is referred to as "mxdn". The radial profile parameters derive primarily from the radial profile function:

We assign a "score" to each value based on its N-sigma relationship to the nominal value displayed by stars (the stellar "ridge"); e.g., for the "sh" score
Thus the parameter score represents the n-sigma value measured for the source of interest. Typical threholds are set a 2*sigma, or a score = 2.0.

The following plots show the scoring results for the candidate galaxies. Every candidate was visually inspected using the JHK images as well as the DSS images and POSS prints (when necessary) in order to classify/verify the objects as follows:

SCMXDN vs Mag : "mxdn" score

The "mxdn" score is derived from the peak pixel brightness versus the integrated flux (using an adaptive circular aperture). Galaxies are denoted by the filled white circles, false galaxies (stars) by small red triangles, double stars by large red triangles, and unknown sources by yellow crosses. The score threshold was set at 2-sigma, or scmxdn = 2. Reminder: the J and H scores are meaningless in this data set.


SCSH vs Mag : "sh" score

The "sh" score is derived from the radial profile, as discussed earlier in this memo. It is effective for most kinds of stars, except double stars and other multiple point source objects.
Reminder: the J and H scores are meaningless in this data set.


SCWSH vs Mag : "wsh" score

The "wsh" score (a.k.a. "wedge shape") is derived similar to the "sh" score, except that it employs a rotating wedge-shaped mask designed to exclude sections of the radial profile from the modified exponential function fit. It's primary purpose is to minimize contamination from double stars.
Reminder: the J and H scores are meaningless in this data set.


The remaining score parameters were designed specifically to counter contamination from multiple stars. Since the COMA field has few doubles and even fewer triple stars (if any), this data set is not useful for testing these "triple killer" parameters.




Reliability

The reliability is measured as follows:

From the last figure below, it can be seen that the reliablity is for the most between 90% and 100% for K< 13.5, which is about what the level-1 specifications are for high galactic latitude fields. Given the relatively few sources (only 1 square degree was covered) these results should not be overinterpreted. The J and H values are meaningless in this data set.