VLT Spectroscopy of Ultra-Faint Dwarf Galaxies. 1. Boötes I, Leo IV, Leo V

Abstract

We perform consistent reductions and measurements for three ultra-faint dwarf galaxies (UFDs): Boötes I, Leo IV and Leo V. Using the public archival data from the GIRAFFE spectrograph on the Very Large Telescope (VLT), we locate new members and provide refined measurements of physical parameters for these dwarf galaxies. We identify nine new Leo IV members and four new Leo V members, and perform a comparative analysis of previously discovered members. Additionally, we identify one new binary star in both Leo IV and Leo V. After removing binary stars, we recalculate the velocity dispersions of Boötes I and Leo IV to be 5.1${}_{-0.8}^{+0.7}$ and 3.4${}_{-0.9}^{+1.3}$ km s${}^{-1}$, respectively; We do not resolve the Leo V velocity dispersion. We identify a weak velocity gradient in Leo V that is $\sim$4$\times$ smaller than the previously calculated gradient and that has a corresponding position angle which differs from the literature value by $\sim$120 deg. Combining the VLT data with previous literature, we re-analyze the Boötes I metallicity distribution function and find that a model including infall of pristine gas while Boötes I was forming stars best fits the data. Our analysis of Leo IV, Leo V and other UFDs will enhance our understanding of these enigmatic stellar populations and contribute to future dark matter studies. This is the first in a series of papers examining thirteen UDFs observed with VLT/GIRAFFE between 2009 and 2017. Similar analyses of the remaining ten UFDs will be presented in forthcoming papers.

29 pages, 18 figures, 8 tables. Accepted for publication on ApJ. Code and data can be found at https://github.com/sazabi4/vlt_dwarf/

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• The Cosmic Hunt for Members in the Outskirts of Ultra Faint Dwarf Galaxies: Ursa Major I, Coma Berenices, and Boötes I
• Metallicity Distribution Functions of 13 Ultra-Faint Dwarf Galaxy Candidates from Hubble Space Telescope Narrowband Imaging
• Photometric Mass Estimation and the Stellar Mass-Halo Mass Relation for Low Mass Galaxies
• The Far-Away Blues: Exploring the Furthest Extents of the Boötes I Ultra Faint Dwarf Galaxy
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• Spectroscopic analysis of Milky Way outer halo satellites: Aquarius II and Bootes II
• Metallicity Distribution Function of the Eridanus~II Ultra-Faint Dwarf Galaxy from Hubble Space Telescope Narrow-band Imaging
• A Statistical Detection of Wide Binary Systems in the Ultra-Faint Dwarf Galaxy Reticulum II
• The LMC impact on the kinematics of the Milky Way satellites: clues from the running solar apex
• Satellite group infall into the Milky Way: exploring the Crater-Leo case with new HST proper motions
• Faint Stars in a Faint Galaxy: II. The Low Mass Stellar Initial Mass Function of the Boötes I Ultrafaint Dwarf Spheroidal Galaxy
• Dark Energy on Astrophysical Scales and Its Detection in the Milky Way
• Classification of gamma-ray targets for velocity-dependent and subhalo-boosted dark-matter annihilation
• A second-generation star in a relic dwarf galaxy
• Densities and mass assembly histories of the Milky Way satellites are not a challenge to $\Lambda$CDM
• Cosmological prior for the $J$-factor estimation of dwarf spheroidal galaxies
• Revisiting the near infrared Calcium triplet as metallicity indicator
• The metal-poorest tail of the Galactic halo: hypothesis on its origin from precise spectral analysis
• The long-term evolution of Ultra Faint Dwarf Galaxies and observational implications
• Chemodynamics of BoötesI with $S^5$: Revised Velocity Gradient, Dark Matter Density, and Galactic Chemical Evolution Constraints
• Carbon measurements in two ultra-faint dwarf galaxies: Grus II and Tucana IV
• EDGE-INFERNO: How chemical enrichment assumptions impact the individual stars of a simulated ultra-faint dwarf galaxy
• Magellan/IMACS spectroscopy of Grus I: A low metallicity ultra-faint dwarf galaxy