Elemental Abundances in And XIX from Coadded Spectra

• Published in: The Astrophysical journal Vol. 972; no. 2; pp. 133 - 152
• Main Authors: Cullinane, L. R., Gilbert, Karoline M., Escala, Ivanna, Wojno, J. Leigh, Kirby, Evan N., Kvasova, Kateryna A., Tollerud, Erik, Collins, Michelle L. M., Rich, R. Michael
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 01.09.2024; IOP Publishing
• Subjects: Abundance; Andromeda Galaxy; Dwarf galaxies; Galaxy mergers & collisions; Kinematics; Local Group; Local group (astronomy); Luminosity; Metallicity; Milky Way; Noise measurement; Red giant stars; Signal to noise ratio; Spectra; Star & galaxy formation; Star formation; Stars & galaxies; Stellar abundances; Stellar mass
• ISSN: 0004-637X; 1538-4357
• DOI: 10.3847/1538-4357/ad5f2e

Abstract With a luminosity similar to that of Milky Way dwarf spheroidal systems like Sextans, but a spatial extent similar to that of ultra-diffuse galaxies, Andromeda (And) XIX is an unusual satellite of M31. To investigate the origin of this galaxy, we measure chemical abundances for And XIX derived from medium-resolution ( R ∼ 6000) spectra from the Deep Extragalactic Imaging Multi-Object Spectrograph on the Keck II telescope. We coadd 79 red giant branch stars, grouped by photometric metallicity, in order to obtain a sufficiently high signal-to-noise ratio to measure 20 [Fe/H] and [ α /Fe] abundances via spectral synthesis. The latter are the first such measurements for And XIX. The mean metallicity we derive for And XIX places it ∼2 σ higher than the present-day stellar mass–metallicity relation for Local Group dwarf galaxies, potentially indicating it has experienced tidal stripping. A loss of gas and associated quenching during such a process, which prevents the extended star formation necessary to produce shallow [ α /Fe]–[Fe/H] gradients in massive systems, is also consistent with the steeply decreasing [ α /Fe]–[Fe/H] trend we observe. In combination with the diffuse structure and disturbed kinematic properties of And XIX, this suggests tidal interactions, rather than galaxy mergers, are strong contenders for its formation.