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Comparing NED and SIMBAD classifications across the contents of nearby galaxies

Cataloguing and classifying celestial objects is one of the fundamental activities of observational astrophysics. In this work, we compare the contents of two comprehensive databases, the NASA Extragalactic Database (NED) and Set of Identifications, Measurements and Bibliography for Astronomical Data (SIMBAD) in the vicinity of nearby galaxies. These two databases employ different classification schemes -- one flat and one hierarchical -- and our goal was to determine the compatibility of classifications for objects in common. Searching both databases for objects within the respective isophotal radius of each of the ~1300 individual galaxies in the Local Volume Galaxy sample, we found that on average, NED contains about ten times as many entries as SIMBAD and about two thirds of SIMBAD objects are matched by position to a NED object, at 5 arcsecond tolerance. These quantities do not depend strongly on the properties of the parent galaxies. We developed an algorithm to compare individual object classifications between the two databases and found that 88% of the classifications agree; we conclude that NED and SIMBAD contain consistent information for sources in common in the vicinity of nearby galaxies. Because many galaxies have numerous sources contained only in one of NED or SIMBAD, researchers seeking the most complete picture of an individual galaxy's contents are best served by using both databases.