Ultra-Faint Milky Way Satellites Discovered in Carina, Phoenix, and Telescopium with DELVE Data Release 3
C. Y. Tan, W. Cerny, A. B. Pace, J. A. Sharp, K. Overdeck, A. Drlica-Wagner, J. D. Simon, B. Mutlu-Pakdil, D. J. Sand, A. M. Senkevich, D. Erkal, P. S. Ferguson, F. Sobreira, K. R. Atzberger, J. L. Carlin, A. Chiti, D. Crnojević, A. P. Ji, L. C. Johnson, T. S. Li, G. Limberg, C. E. Martínez-Vázquez, G. E. Medina, V. M. Placco, A. H. Riley, E. J. Tollerud, A. K. Vivas, T. M. C. Abbott, M. Aguena, O. Alves, D. Bacon, S. Bocquet, D. Brooks, D. L. Burke, R. Camilleri, J. A. Carballo-Bello, A. Carnero Rosell, J. Carretero, T. -Y. Cheng, Y. Choi, L. N. da Costa, M. E. da Silva Pereira, T. M. Davis, J. De Vicente, S. Desai, P. Doel, S. Everett, B. Flaugher, J. Frieman, J. García-Bellido, D. Gruen, G. Gutierrez, S. R. Hinton, D. L. Hollowood, D. J. James, K. Kuehn, S. Lee, J. L. Marshall, J. Mena-Fernández, F. Menanteau, R. Miquel, J. Myles, M. Navabi, D. L. Nidever, R. L. C. Ogando, A. A. Plazas Malagón, A. Porredon, S. Samuroff, E. Sanchez, D. Sanchez Cid, I. Sevilla-Noarbe, M. Smith, E. Suchyta, M. E. C. Swanson, V. Vikram, A. R. Walker, A. Zenteno
Abstract
We report the discovery of three Milky Way satellite candidates: Carina IV, Phoenix III, and DELVE 7, in the third data release of the DECam Local Volume Exploration survey (DELVE). The candidate systems were identified by cross-matching results from two independent search algorithms. All three are extremely faint systems composed of old, metal-poor stellar populations ($τ\gtrsim 10$ Gyr, [Fe/H] $ \lesssim -1.4$). Carina IV ($M_V = -2.8;\ r_{1/2} = 40 {\rm pc}$) and Phoenix III ($M_V = -1.2;\ r_{1/2} = 19 {\rm pc}$) have half-light radii that are consistent with the known population of dwarf galaxies, while DELVE 7 ($M_V = 1.2;\ r_{1/2} = 2 {\rm pc}$) is very compact and seems more likely to be a star cluster, though its nature remains ambiguous without spectroscopic followup. The Gaia proper motions of stars in Carina IV ($M_* = 2250^{+1180}_{-830} {\rm M_\odot}$) indicate that it is unlikely to be associated with the LMC, while DECam CaHK photometry confirms that its member stars are metal-poor. Phoenix III ($M_* = 520^{+660}_{-290} {\rm M_\odot}$) is the faintest known satellite in the extreme outer stellar halo ($D_{\rm GC} > 100$ kpc), while DELVE 7 ($M_* = 60^{+120}_{-40} {\rm M_\odot}$) is the faintest known satellite with $D_{\rm GC} > 20$ kpc.