NYU Value-Added Galaxy Catalog
In the object_sdss_spectro and object_sdss_tiling files we only matched spectra or tiled objects to NYU-VAGC objects with 2 arcsec. However, for low surface brightness or complex galaxies, the behavior of the deblender has changed as the photometric software has changed over time. Thus, the spectrum may include significant flux from an object in the latest SDSS imaging catalog, but not be near the nominal center of that object. We would like to make sure that we can recover the redshifts of objects in these cases.
In order to do so, we take all objects in the object_sdss_imaging file file that have no spectroscopic matches, and compare them to all spectra in the SDSS spectroscopic catalog that are not already matched to resolved objects and which are within twice the Petrosian 90% light radius of the center of the object. For each object we take a 3 arcsec radius aperture around the center of each nearby spectrum, and measure the flux contributed by the object in question (or its parent, if the quality flag USE_PARENT is set). If this flux is at least half of the total flux in the imaging at that location, than we consider the given spectrum to match the given object. We perform the same operation for the tiling catalog.
The results are stored in:
$VAGC_REDUX/matchspec/matchspec.fits $VAGC_REDUX/matchspec/matchtiled.fitswhich have the following columns: