Kavli Affiliate: Alexander P. Ji
| First 5 Authors: Nathan R. Sandford, Nathan R. Sandford, , ,
| Summary:
We combine new spectroscopic observations of the ultra faint dwarf galaxy
(UFD) Bo"otes I (Boo I) from the Southern Stellar Stream Spectroscopic Survey
($S^5$) with $sim$15 years of archival spectroscopic data to create the
largest sample of stellar kinematics and metallicities to date in any Milky Way
UFD. Our combined sample includes 148 members extending out to $sim$7
half-light radii ($r_h$), including 24 newly confirmed members, 18 binary
candidates, 15 RR Lyrae stars, and 92 [Fe/H] measurements. Using this larger
and more spatially extended sample, we provide updated constraints on Boo I’s
systemic properties, including its radial population gradients. Properly
accounting for perspective rotation effects in a UFD for the first time, we
detect a $4sigma$ line-of-sight velocity gradient of $1.2pm0.3$ km s$^-1$
$r_h^-1$ aligned along Boo I’s orbit and discuss its potential tidal origins.
We also infer a metallicity gradient of $-0.10pm0.02$ dex $r_h^-1$ in
agreement with previous studies. Using an axisymmetric Jeans model, we provide
updated constraints on Boo I’s dark matter density profile, which weakly favor
a cusped ($gamma=1.0^+0.5_-0.6$) dark matter profile. Lastly, we
re-analyze Boo I’s metallicity distribution function with a one-zone galactic
chemical evolution model and place new constraints on its rapid, inefficient
star formation and strong galactic outflows.
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