VLT Spectroscopy of Ultra-Faint Dwarf Galaxies. 1. Bo\"otes I, Leo IV, Leo V

TL;DR

This study uses VLT spectroscopy to identify new members and refine physical parameters of ultra-faint dwarf galaxies Boötes I, Leo IV, and Leo V, providing insights into their kinematics and metallicity distributions to aid dark matter research.

Contribution

First comprehensive VLT spectroscopic analysis of three ultra-faint dwarf galaxies, identifying new members and refining their velocity and metallicity measurements.

Findings

Recalculated velocity dispersions: Boötes I 5.1 km/s, Leo IV 3.4 km/s.

Identified new binary stars in Leo IV and Leo V.

Detected a weak velocity gradient in Leo V with a different position angle.

Abstract

We perform consistent reductions and measurements for three ultra-faint dwarf galaxies (UFDs): Bo\"otes 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 Bo\"otes I and Leo IV to be 5.1$^{+0.7}_{-0.8}$ and 3.4$^{+1.3}_{-0.9}$ 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 Bo\"otes I metallicity distribution function and find that a model including infall of pristine gas while Bo\"otes 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.