Gravitational Wave Followup Overview

Welcome to the NED Gravitational Wave Follow-up (GWF) Service

The purpose of this new NED service is to facilitate searches for electromagnetic (EM) counterparts to gravitational wave (GW) events. Within minutes after the Laser Interferometer Gravitational-Wave Observatory (LIGO)-Virgo collaboration issues an alert using the Gamma-ray Coordinates Network (GCN) operated by the NASA GSFC (, this NED service responds by crossmatching in 3D the event's HEALPix map with the galaxies in the local Universe and the following results are provided: an all-sky image of the probability contours, the location of all galaxies in NED within the LIGO 90% probability volume, and the top 20 galaxies sorted by 2MASS absolute Ks-band magnitude. To get started, click on "Events" in the menu above or simply click on the (blue) button below for the most recent GW event.

Note: The NED and Census of the Local Universe (CLU) projects are issuing a joint notice of candidate galaxies for each LIGO GW trigger. While a large fraction of the galaxies in CLU catalog come from NED, there are galaxies in CLU that have not yet been ingested into NED, and NED is continually updating its holdings. Thus, some of the CLU top 20 galaxies listed in the GCN notices may not be in the NED list on this website. The NED service sorts its galaxies by absolute K-band magnitude. However, the overall composition of the CLU and NED galaxy lists will be similar.


Figure 1: Example LIGO sky localizations.

Gravitational Waves have opened an exciting new window into the Universe by enabling the direct study of the merger of massive, compact objects. Our understanding of these events is greatly enhanced by identifying and studying their EM counterparts in a new field known as multi-messenger astronomy. The sky localizations for GW events detected by LIGO are generally quite large (> 100 square degrees; see Figure 1), making this task very challenging. However, an effective strategy to increase the efficiency of observational followup campaigns is to search for GW afterglows by targeting galaxies in the highest probability volume of the GW event.

This new service exploits the rich and constantly growing content of the NASA/IPAC Extragalactic Database (NED) to help astronomers around the world efficiently search for the EM counterparts to GW events. An overview of the process is as follows: A list of galaxies in the local Universe is constructed by using available redshift and redshift-independent distances. Components of galaxies, galaxy groups, and clusters are omitted to keep the sample confined to candidate host galaxies for the GW event. Currently redshift-independent distances are selected (when available) over redshift measurements, and the median of the individual redshift-independent distances is used as the final distance when multiple measurements are available. To match the targeted sensitivity of LIGO to merging neutron stars, and accounting for the uncertainties in some galaxy distances, a distance of 200 Mpc is used to define a NED Local Universe Sample. As of February 2019, this local volume contains 234,910 galaxies, with 27,434 having redshift-independent distances.

The NED GW follow-up service listens to public alerts on the Gamma-ray Coordinates Network (GCN), which is used by LIGO to distribute GW event information. After each GW event, the HEALPix map is crossmatched in 3D to the NED galaxy list. During this process an all-sky image of the probability contours, the location of all galaxies in the 90% volume, and the top 20 galaxies sorted by 2MASS absolute Ks-band magnitude are displayed on each event's page. The list is sorted by the absolute Ks magnitude because evidence to date suggests that binary mergers that contain a neutron star (NS-NS or BN-NS) are likely to occur in more evolved, more massive galaxies, and because the NIR light more closely traces the older stellar population of a galaxy and hence is a proxy for stellar mass.

Last update: 2019-03-13 17:58:13 PST