THE CHEMISTRY OF THE TRAILING ARM OF THE SAGITTARIUS DWARF GALAXY
We present abundances of C, O, Ti, and Fe for 11 M-giant stars in the trailing tidal arm of the Sagittarius dwarf (Sgr). The abundances were derived by comparing synthetic spectra with high-resolution infrared spectra obtained with the Phoenix spectrograph on the Gemini South telescope. The targeted stars are drawn from two regions of the Sgr trailing arm separated by 66{sup 0} (five stars) and 132{sup 0} (six stars) from the main body of Sgr. The trailing arm provides a more direct diagnostic of the chemical evolution of Sgr compared to the extensively phase-mixed leading arm. Within our restricted sample of {approx}2-3 Gyr old stars, we find that the stream material exhibits a significant metallicity gradient of -(2.4 {+-} 0.3) x 10{sup -3} dex/degree (-(9.4 {+-} 1.1) x 10{sup -4} dex/kpc) away from the main body of Sgr. The tidal disruption of Sgr is a relatively recent event. We therefore interpret the presence of a metallicity gradient in the debris as indicative of a similar gradient in the progenitor. The fact that such a metallicity gradient survived for almost a Hubble time indicates that the efficiency of radial mixing was very low in the Sgr progenitor. No significant gradient is seen to exist in the [{alpha}/Fe] abundance ratio along the trailing arm. Our results may be accounted for by a radial decrease in star formation efficiency and/or radial increase in the efficiency of galactic wind-driven metal loss in the chemical evolution of the Sgr progenitor. The [Ti/Fe] and [O/Fe] abundance ratios observed within the stream are distinct from those of the Galactic halo. We conclude that the fraction of the intermediate to metal-rich halo population contributed by the recent dissolution (<3 Gyr) of Sgr-like dwarf galaxies cannot be substantial.
- OSTI ID:
- 21460095
- Journal Information:
- Astrophysical Journal, Vol. 720, Issue 1; Other Information: DOI: 10.1088/0004-637X/720/1/940; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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