Redshift-Independent Distances in the NASA/IPAC Extragalactic Database: Methodology, Content and Use of NED-D

TL;DR

This paper details the methodology, content, and applications of NED-D, a comprehensive database of over 100,000 redshift-independent galaxy distance estimates used in astrophysics research.

Contribution

It provides the first detailed overview of NED-D, including its compilation process, the variety of distance indicators used, and its significance for extragalactic distance measurements.

Findings

NED-D contains over 100,000 distance estimates for 28,000 galaxies.

75 different distance indicators are utilized in the database.

The database facilitates comparison of distance indicators across a wide range of distances.

Abstract

Estimates of galaxy distances based on indicators that are independent of cosmological redshift are fundamental to astrophysics. Researchers use them to establish the extragalactic distance scale, to underpin estimates of the Hubble constant, and to study peculiar velocities induced by gravitational attractions that perturb the motions of galaxies with respect to the Hubble flow of universal expansion. In 2006 the NASA/IPAC Extragalactic Database (NED) began making available a comprehensive compilation of redshift-independent extragalactic distance estimates. A decade later, this compendium of distances (NED-D) now contains more than 100,000 individual estimates based on primary and secondary indicators, available for more than 28,000 galaxies, and compiled from over 2,000 references in the refereed astronomical literature. This article describes the methodology, content, and use of NED-D, and addresses challenges to be overcome in compiling such distances. Currently, 75 different distance indicators are in use. We include a figure that facilitates comparison of the indicators with significant numbers of estimates in terms of the minimum, 25th percentile, median, 75th percentile, and maximum distances spanned. Brief descriptions of the indicators, including examples of their use in the database, are given in an Appendix.