Reading between the (Spectral) Lines: Magellan/IMACS Spectroscopy of the Ultrafaint Dwarf Galaxies Eridanus IV and Centaurus I

• DOI: 10.3847/1538-4357/ad0cf7
• Publication Date: 2024-01-30T15:10:39Z
• Authors: M. E. Heiger; T. S. Li; A. B. Pace; J. D. Simon; A. P. Ji; A. Chiti; C. R. Bom; J. A. Carballo-Bello; J. L. Carlin; W. Cerny; Y. Choi; A. Drlica-Wagner; D. J. James; C. E. Martínez-Vá...; G. E. Medina; B. Mutlu-Pakdil; M. Navabi; N. E. D. Noël; J. D. Sakowska; G. S. Stringfellow
• Keywords: Galaxy Formation and Evolution in the Universe; Physics; FOS: Physical sciences; Astronomy and Astrophysics; Stellar Astrophysics and Exoplanet Studies; Astrophysics; Astrophysics - Astrophysics of Galaxies; Computer science; QB460-466; Algorithm; Star Formation in Molecular Clouds and Protoplanetary Disks; Physics and Astronomy; Astrophysics of Galaxies (astro-ph.GA); Physical Sciences; Local Group; Young Stellar Objects; Dwarf galaxies; Spectroscopy

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.