Dear All,<div><br></div><div>I apologize for leaving yesterday before the end of teleconf ..... </div><div>here it's an update about completeness and its implementation within KIDSCAT. </div><div> </div><div>The completeness algorithm is based on the idea of Garilli+99, A&A, 342, 408, </div>
<div>where one determines the magnitude at which objects start to be lost in the catalog because they are </div><div>below the brightness threshold in the detection cell. You can see an application of this algorithm</div>
<div>to SDSS and UKIDSS data in our SPIDER-I paper, La Barbera et al. 2010MNRAS.408.1313L (e.g. Fig.~22).</div><div><br></div><div>Completeness is computed using the MAG_AUTO vs. DETECTION_MAG diagram, as illustrated, for one field,</div>
<div>in the attached jpg file, COMPL_Sci-DBOXHOORN-OMEGACAM-------OCAM_g_SDSS---Coadd---Sci-56240.5315550-6.jpg.</div><div>The bz2 archive also includes the same kind of plots (automatically produced when running KIDSCAT) for all the 52 images.</div>
<div><br></div><div>Symbols in the plot(s) are:</div><div>blue dots -> stars, according to KIDSCAT classification</div><div>grey dots -> objects whose MAG_AUTO and DETECTION_MAG have low S/N (<5 and 4, respectively). These are excluded</div>
<div>in the computation of the limiting mag to make the computation of detection limit more stable (see below).</div><div>black dots -> all remaining sources in the catalog (considering only objects with S-Ex and IMA flags=0)</div>
<div><br></div><div>Notice that since we do not have the detection brightness for the sources, I'm using the 2pixels diam. mag from KIDSCAT</div><div>as a proxy for it (hereafter, and in the plots, I refer to this as DETECTION_MAG). This approximation should be OK for most purposes.</div>
<div>The distiibution of points in the diagram is approximately limited, by construction (S-Ex detects objects if they are above a given S/N</div><div>in the detection cell), wrt DETECTION_MAG. I determine the detection limit (vertical dashed line) by binning the data wrt</div>
<div>MAG_AUTO, and computing in each bin the 98-th percentile of the DETECTION_MAG distribution. This gives us the red, solid, curve </div><div>in the diagram. A fixed part of the red curve, *below* the detection limit, is fitted by a least-squares line (cyan line).</div>
<div>The intersection of the cyan line with the detection limit (red, dashed line), gives you the completeness magnitude of the catalog</div><div>(horizontal dashed line). By construction, the catalog should be more than 98% complete below this completeness value.</div>
<div><br></div><div>Notice that one might use a second-order polynomial fit, rather than a line, to model the solid, red, curve. After several </div><div>experiments, I decided to keep the linear fit. It gives more stable results (in any case, the completeness estimates do not change </div>
<div>by more than 0.1-0.2mags). Notice that for u-band, because of the low number of galaxies with good S/N, the completeness</div><div>estimates are somewhat uncertain, but still reasonable, in my view.</div><div><br></div>
<div>Of course, using external, deeper photometric catalogs, would help us to obtain independent estimates of completeness,</div><div>to compare with our internal ones. </div><div><br></div><div>As usual, any comment/suggestion is more than welcome !! </div>
<div><br></div><div>Cheers,</div><div>Francesco</div><div><br></div>