2025ApJ...984..148C

We present deep Magellan+Megacam imaging of Centaurus I (Cen I) and Eridanus IV (Eri IV), two recently discovered Milky Way ultrafaint satellites. Our data reach ∼2-3 mag deeper than the discovery data from the DECam Local Volume Exploration Survey. We use these data to constrain their distances, structural properties (e.g., half-light radii, ellipticity, and position angle), and luminosities. We investigate whether these systems show signs of tidal disturbance and identify new potential member stars using Gaia EDR3. Our deep color-magnitude diagrams show that Cen I and Eri IV are consistent with an old (τ ∼ 13.0 Gyr) and metal-poor ([Fe/H] ≤ -2.2) stellar population. We find Cen I to have a half-light radius of ${r}_{h}=2.\,^{\prime} 60\pm 0.\,^{\prime} 30\,$(90.6 ± 11 pc), an ellipticity of ϵ = 0.36 ± 0.05, a distance of D = 119.8 ± 4.1 kpc (m - M = 20.39 ± 0.08 mag), and an absolute magnitude of M_V = -5.39 ± 0.19. Similarly, Eri IV has ${r}_{h}=3.\,^{\prime} 24\pm 0.\,^{\prime} 48\,$(65.9 ± 10 pc), ϵ = 0.26 ± 0.09, D = 69.9 ± 3.6 kpc (m - M = 19.22 ± 0.11 mag), and M_V = -3.55 ± 0.24. These systems occupy a space on the size-luminosity plane consistent with other known Milky Way dwarf galaxies, which supports the findings from our previous spectroscopic follow-up. Cen I has a well-defined morphology that lacks any clear evidence of tidal disruption, whereas Eri IV hosts a significant extended feature with multiple possible interpretations.