2016ApJ...818...39H -
Astrophys. J., 818, 39 (2016/February-2)
Evidence that Hydra I is a tidally disrupting Milky Way dwarf galaxy.
HARGIS J.R., KIMMIG B., WILLMAN B., CALDWELL N., WALKER M.G., STRADER J., SAND D.J., GRILLMAIR C.J. and YOON J.H.
Abstract (from CDS):
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[α/Fe] = 0.09 ± 0.03 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 [α/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.
Abstract Copyright:
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Journal keyword(s):
galaxies: dwarf - Galaxy: halo - Galaxy: structure
VizieR on-line data:
<Available at CDS (J/ApJ/818/39): table1.dat table2.dat table3.dat>
Nomenclature:
Table 2: [HKW2016] DDD.dddddd+DD.dddddd N=411.
Simbad objects:
669
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