A Study Of Galaxy Completeness Limits In NED

A Study Of Galaxy Completeness Limits In NED

I wanted to generate a few plots to show the extent of the incompleteness and the anisotropy of the sample of galaxies catalogued in NASA/IPAC Extragalactic Database (NED). Below is plot of a northern section of the probability map of the gravitational wave GW1509141, overlaid with the PS1 survey footprint and all galaxies catalogued in NED within that footprint. The sharp drop in galaxy counts below dec \(\sim-3^{\circ}\) serves to reveal the boundary of SDSS DR62.

Apart from SDSS there are three other main survey footprints:

  1. WINGS (WIde-field Nearby Galaxy-cluster Survey) survey of a complete, X-ray selected sample of galaxy clusters in the redshift range 0.04–0.07.

  2. The Las Campanas Redshift Survey (LCRS) consists of 26,418 redshifts of galaxies selected from a CCD-based catalog obtained in the R band. The survey covers over 700 deg2 in six strips, each 1.5deg x 80deg, three each in the north and south Galactic caps

  3. The Cosmological Evolution Survey (COSMOS). From the COSMOS website:

The Cosmological Evolution Survey (COSMOS) is an astronomical survey designed to probe the formation and evolution of galaxies as a function of both cosmic time (redshift) and the local galaxy environment. The survey covers a 2 square degree equatorial field with imaging by most of the major space-based telescopes and a number of large ground based telescopes, with many ongoing surveys. Over 2 million galaxies are detected, spanning 75% of the age of the Universe

Comparing Equal-Area Samples of Galaxies

Using two equal-area samples of galaxies catalogued in NED, one within the SDSS footprint and one outside of the SDSS footprint, we can compare the completeness of the samples. I decided to repeat this process 3 times for 3 different pairs of sample areas with search radii of \(2.5^{\circ}\) at the coordinates shown in the tables.


Parameter SDSS Non–SDSS Total Sources w/ Axis Measurements
RA 140.0 153.0 1673 1512
DEC 6.0 -12.0 519 80


Parameter SDSS Non–SDSS Total Sources w/ Axis Measurements
RA 149.0 152.0 31047 4091
DEC 2.0 -7.0 1102 999


Parameter SDSS Non–SDSS Total Sources w/ Axis Measurements
RA 132.0 154.0 1223 1120
DEC 4.0 -16.5 171 63


As you can see the depth of completeness of catalogued galaxies within SDSS far outstrip the completeness of those catalogued outside. This shows the importance of pushing ahead with all-sky surveys (e.g. PanSTARRS and LSST).

  1. the previous placeholder name for GW150914 was G184098  ↩

  2. DR6 is the highest SDSS release in NED as of 20160405  ↩