Journal
ASTROPHYSICAL JOURNAL
Volume 736, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0004-637X/736/2/146
Keywords
galaxies: dwarf; galaxies: individual (Bootes I); galaxies: kinematics and dynamics; methods: data analysis; techniques: radial velocities
Categories
Funding
- Chilean Center for Astrophysics FONDAP [15010003]
- BASAL Center for Astrophysics and Associated Technologies CATA [PFB-06/2007]
- NASA [HST-HF-51283]
- Space Telescope Science Institute
- [NAS 5-26555]
- STFC [ST/H002235/1, ST/H001913/1] Funding Source: UKRI
- Science and Technology Facilities Council [ST/H001913/1, ST/H00243X/1, ST/H002235/1] Funding Source: researchfish
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We develop, implement, and characterize an enhanced data reduction approach which delivers precise, accurate, radial velocities from moderate resolution spectroscopy with the fiber-fed VLT/FLAMES+GIRAFFE facility. This facility, with appropriate care, delivers radial velocities adequate to resolve the intrinsic velocity dispersions of the very faint dwarf spheroidal (dSph) galaxies. Importantly, repeated measurements let us reliably calibrate our individual velocity errors (0.2 km s(-1) <= delta(V) <= 5 km s(-1)) and directly detect stars with variable radial velocities. We show, by application to the Bootes I dSph, that the intrinsic velocity dispersion of this system is significantly below 6.5 km s(-1) reported by previous studies. Our data favor a two-population model of Bootes I, consisting of a majority cold stellar component, with velocity dispersion 2.4(-0.5)(+0.9) km s(-1), and a minority hot stellar component, with velocity dispersion similar to 9 km s(-1), although we cannot completely rule out a single component distribution with velocity dispersion 4.6(-0.6)(0.8) km s(-1). We speculate that this complex velocity distribution actually reflects the distribution of velocity anisotropy in Bootes I, which is a measure of its formation processes.
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