Too many low redshift galaxies in NED database When using the NED database I found there are too many galaxies with very low redshift (Near zero). I used NEDs search by parameters function to find all galaxies within Z=0 to Z=.03 redshift. I did this in three separate queries( 0 to .01, .01 to .02, and .02 to .03). This means I double counted the galaxies at .01 and .02. There could also be some rounding mischief adding to the spikes. My MAIN concern is the huge spike near redshift Z=0. Why is this spike present? could it be a large number of galaxies with negative redshift are being rounded to zero? This explanation does not seem to be enough. Any input is appreciated!
If you want a link to the NED website here it is https://ned.ipac.caltech.edu/byparams

 A: Because the catalogues are nowhere near being complete and it is much easier to find and catalogue nearby extragalactic objects.
Galaxies come with a vast range of masses and luminosities. The distribution of number density of galaxies with luminosity is known as the luminosity function. Galaxies more luminous than the Milky Way are very rare, but lower luminosity galaxies increase by about an order of magnitude for each order of magnitude decrease in luminosity.
When a galaxy redshift survey is done, the results will be flux-limited, so that at increasing redshift, an increasing fraction of the galaxy population lies below the flux threshold. Low redshift surveys might detect dwarf galaxies with luminosities orders of magnitude lower in luminosity than the Milky Way in large numbers. But these will not be detected in high redshift surveys because they are too faint.
An additional factor is that surveys that are designed to detect low redshift galaxies will usually cover a large area on the sky. In particular, the local volume has been thoroughly searched in most directions. In contrast, surveys designed to detect high redshift galaxies will be forced to look at small regions because they require extremely deep exposures and even then are often only finding the comparatively rare, high-luminosity galaxies at that redshift.
Whilst all of the above are important factors in explaining the redshift distribution of a database like NED, they do not explain your spike at very low redshift.
Indeed the following plot (from here) of the redshift distribution of objects in NED (top left, green curve) suggests it isn't there.

A: The NED help desk responded to my question. They have also found the over density of objects near Z=0. They have identified a large fraction of these objects to be contaminants via automated assessment and visual classification. While there are many reasons for these contaminants for individual objects, a large fraction of them can be separated into two categories: 1) Galactic stars with redshifts misclassified as galaxies in various large survey catalogs and 2) objects with unreliable redshifts that were not properly flagged as suspect in some input catalogs.
They will be submitting their findings in an article sometime in the next month or two (Cook et al. 2022; in prep, “Completeness of the NASA/IPAC Extragalactic Database (NED) - Local Volume Sample"), where the appendices provide lists of these objects.
