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Determine host association of SAGA background galaxies

Determine whether the galaxies classified as "background" in the SAGA DR3 redshift catalog—objects within the SAGA footprint but not meeting the satellite criteria relative to the listed Milky Way–mass hosts—are satellites of other nearby Milky Way–mass systems not included in the SAGA host sample or are truly isolated field galaxies, by establishing their group membership and host associations using environmental and kinematic information.

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Background

The SAGA DR3 redshift catalog includes all galaxies with confirmed redshifts within the SAGA footprint (10–300 kpc in projection around each host). Satellites are defined by being fainter than the host, within 300 kpc in projection, and within ±275 km/s of the host’s heliocentric velocity; galaxies that do not meet these criteria are labeled "background."

Because the catalog focuses on selected SAGA hosts, some galaxies labeled "background" in the footprint could still be satellites of other nearby systems that were not part of the SAGA host selection. The authors explicitly note that this classification ambiguity remains unresolved and motivates a clearer determination of host associations for these galaxies.

References

Note that while these background galaxies are not satellites of one of the \nhosts{} SAGA systems, we do not know whether they are satellite galaxies of another system that is not part of the SAGA host sample.

— The SAGA Survey. III. A Census of 101 Satellite Systems around Milky Way-mass Galaxies (2404.14498 - Mao et al., 22 Apr 2024) in Section 4.4 (SAGA Background Sample)