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Heiger, M. E.; Li, T. S.; Pace, A. B.; Simon, J. D.; Ji, A. P.; Chiti, A.; Bom, C. R.; Carballo-Bello, J. A.; Carlin, J. L.; Cerny, W.; Choi, Y.; Drlica-Wagner, A.; James, D. J.; Martínez-Vázquez, C. E.; Medina, G. E.; Mutlu-Pakdil, B.; Navabi, M.; Noël, N. E. D.; Sakowska, J. D.; Stringfellow, G. S.
Astrophysical journal/The Astrophysical journal, 02/2024, Volume: 961, Issue: 2Journal Article
Abstract We present a spectroscopic analysis of Eridanus IV (Eri IV) and Centaurus I (Cen I), two ultrafaint dwarf galaxies of the Milky Way. Using IMACS/Magellan spectroscopy, we identify 28 member stars of Eri IV and 34 member stars of Cen I. For Eri IV, we measure a systemic velocity of v sys = − 31.5 − 1.2 + 1.3 km s − 1 , and velocity dispersion σ v = 6.1 − 0.9 + 1.2 km s − 1 . Additionally, we measure the metallicities of 16 member stars of Eri IV. We find a metallicity of Fe / H = − 2.87 − 0.07 + 0.08 , and resolve a dispersion of σ Fe/H =0.20 ± 0.09. The mean metallicity is marginally lower than all other known ultrafaint dwarf galaxies, making it one of the most metal-poor galaxies discovered thus far. Eri IV also has a somewhat unusual right-skewed metallicity distribution. For Cen I, we find a velocity v sys = 44.9 ± 0.8 km s −1 , and velocity dispersion σ v = 4.2 − 0.5 + 0.6 km s − 1 . We measure the metallicities of 27 member stars of Cen I, and find a mean metallicity Fe/H = −2.57 ± 0.08, and metallicity dispersion σ Fe / H = 0.38 − 0.05 + 0.07 . We calculate the systemic proper motion, orbit, and the astrophysical J-factor for each system, the latter of which indicates that Eri IV is a good target for indirect dark matter detection. We also find no strong evidence for tidal stripping of Cen I or Eri IV. Overall, our measurements confirm that Eri IV and Cen I are dark-matter-dominated galaxies with properties largely consistent with other known ultrafaint dwarf galaxies. The low metallicity, right-skewed metallicity distribution, and high J-factor make Eri IV an especially interesting candidate for further follow-up.
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