The Eastern Banded Structure (EBS) and Hydra I halo overdensities are very nearby (d ∼ 10 kpc) objects discovered in Sloan Digital Sky Survey (SDSS) data. Previous studies of the region have shown that EBS and Hydra I are spatially coincident, cold structures at the same distance, suggesting that Hydra I may be the EBS's progenitor. We combine new wide-field Dark Energy Camera (DECam) imaging and MMT/Hectochelle spectroscopic observations of Hydra I with SDSS archival spectroscopic observations to quantify Hydra I's present-day chemodynamical properties, and to infer whether it originated as a star cluster or dwarf galaxy. While previous work using shallow SDSS imaging assumed a standard old, metal-poor stellar population, our deeper DECam imaging reveals that Hydra I has a thin, well-defined main sequence turnoff of intermediate age (∼5-6 Gyr) and metallicity ([Fe/H] = -0.9 dex). We measure statistically significant spreads in both the iron and alpha-element abundances of σ[Fe/H] = 0.13 ± 0.02 dex and σ[/Fe] = 0.09 ± 0.03 and dex, respectively, and place upper limits on both the rotation and its proper motion. Hydra I's intermediate age and [Fe/H] - as well as its low [/Fe], apparent [Fe/H] spread, and present-day low luminosity - suggest that its progenitor was a dwarf galaxy, which has subsequently lost more than 99.99% of its stellar mass.
|Original language||English (US)|
|State||Published - Feb 10 2016|
- Galaxy: halo
- Galaxy: structure
- galaxies: dwarf
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science
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Hydra I wide-field imaging and spectroscopy obs.
Hargis, J. R. (Creator), Kimmig, B. (Creator), Willman, B. (Creator), Caldwell, N. (Creator), Walker, M. G. (Creator), Strader, J. (Creator), Sand, D. J. (Creator), Grillmair, C. J. (Creator) & Yoon, J. H. (Creator), Centre de Donnees Strasbourg (CDS), 2016
DOI: 10.26093/cds/vizier.18180039, https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/818/39