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Cerny, W.; Pace, A. B.; Drlica-Wagner, A.; Koposov, S. E.; Vivas, A. K.; Mau, S.; Riley, A. H.; Bom, C. R.; Carlin, J. L.; Choi, Y.; Erkal, D.; Ferguson, P. S.; James, D. J.; Li, T. S.; Martínez-Delgado, D.; Martínez-Vázquez, C. E.; Munoz, R. R.; Mutlu-Pakdil, B.; Olsen, K. A. G.; Pieres, A.; Sakowska, J. D.; Sand, D. J.; Simon, J. D.; Smercina, A.; Stringfellow, G. S.; Tollerud, E. J.; Adamów, M.; Hernandez-Lang, D.; Kuropatkin, N.; Santana-Silva, L.; Tucker, D. L.; Zenteno, A.
Astrophysical journal. Letters, 10/2021, Volume: 920, Issue: 2Journal Article
Abstract We present the discovery of a candidate ultra-faint Milky-Way satellite, Eridanus IV (DELVE J0505−0931), detected in photometric data from the DECam Local Volume Exploration survey (DELVE). Eridanus IV is a faint ( M V = − 4.7 ± 0.2), extended ( r 1 / 2 = 75 − 13 + 16 pc ), and elliptical ( ϵ = 0.54 ± 0.1) system at a heliocentric distance of 76.7 − 6.1 + 4.0 kpc , with a stellar population that is well described by an old, metal-poor isochrone (age of τ ∼ 13.0 Gyr and metallicity of Fe/H ≲ − 2.1 dex). These properties are consistent with the known population of ultra-faint Milky-Way satellite galaxies. Eridanus IV is also prominently detected using proper-motion measurements from Gaia Early Data Release 3, with a systemic proper motion of ( μ α cos δ , μ δ ) = ( + 0.25 ± 0.06 , − 0.10 ± 0.05 ) mas yr −1 measured from its horizontal branch and red-giant-branch member stars. We find that the spatial distribution of likely member stars hints at the possibility that the system is undergoing tidal disruption.
