Very Large Telescope Spectroscopy of Ultra-faint Dwarf Galaxies. I. Boötes I, Leo IV, and 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 +0.7 −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 ∼4× smaller than the previously calculated gradient and that has a corresponding position angle which differs from the literature value by ∼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.

Proper Motions, Orbits, and Tidal Influences of Milky Way Dwarf Spheroidal Galaxies

“…2006) (c)(Martin et al 2007) (d)(Koposov et al 2011) (e)(Jenkins et al 2021) (f)(Koch et al 2009) (g)(Ji et al 2016) (h)(Carlin et al 2009) (i)(Simon & Geha 2007) (j)(Li et al 2018a) (k)(Ji et al 2020) (l)(Fritz et al 2019) (m) (Martin et al 2016a) (n) (Longeard et al 2018) (o) (Li et al 2017) (p) (Zoutendijk et al 2021) (q) (Walker et al 2016) (r) (Simon et al 2020) (s) (Koposov et al 2015b) (t) (Nagasawa et al 2018) (u) (Kirby et al 2015) (v) (Koposov et al 2018) (w) (Collins et al 2017) (x) (Mutlu-Pakdil et al 2019) (y) (Kim et al 2016) (z) (Walker et al 2015a) (aa) (Simon et al 2015) (ab) (Longeard et al 2020) (ac) (Norris et al 2010) (ad) (Simon et al 2011) (ae) (Kirby et al 2013) (af) (Belokurov et al 2009) (ag) (Martin et al 2016b) (ah) (Kirby et al 2017) (ai) (Chiti et al 2018) (aj) (Chiti et al 2021) (ak) (Simon et al 2017) (al) (Li et al 2018b) (am) (Kleyna et al 2005) (an) (Willman et al 2011)…”

Faint Stars in a Faint Galaxy. II. The Low-mass Stellar Initial Mass Function of the Boötes I Ultrafaint Dwarf Spheroidal Galaxy

“…These cluster around the origin (zero relative proper motion). The internal line-of-sight velocity dispersion of Boo I is ∼5 km s −1 (Jenkins et al 2021), giving an expected one-dimensional proper-motion dispersion of ∼0.015 mas yr −1 (assuming isotropic velocity dispersion tensor and a distance of 65 kpc), which is too small to be measured with these proper motions, given their errors. That said, the VPD contains only a few stars outside of the tight cluster centered on (0,0).…”

The Pristine dwarf galaxy survey – IV. Probing the outskirts of the dwarf galaxy Boötes I

“…To identify the final number of new member stars found, both the AAT sample and the data sets from the literature are used. The literature data sets are mainly constituted of Martin et al ( 2007 ), Norris et al ( 2008Norris et al ( , 2010a, Koposov et al ( 2011 ), andJenkins et al ( 2021 ). Some of the stars in these data sets have been reobserved at higher resolution through the years (Feltzing et al 2009 ;Norris et al 2010b ;Lai et al 2011 ;Gilmore et al 2013 ;Ishigaki et al 2014 ;Frebel et al 2016 ).…”

“…This exceptionally large FoV combined with the Gaia Data Release 3 and the Pristine surv e y enables us to probe the outskirts of Boo I up to a distance of 4.1 half-light radii ( r h ). Boo I was disco v ered by Belokurov et al ( 2006 ) and is the most e xtensiv ely spectroscopically studied UFD (see Martin et al 2007 ;Norris et al 2008Norris et al , 2010aKoposov et al 2011 ;Jenkins et al 2021 for studies identifying new Boo I members and not reanalysing known Boo I stars at high resolution). These studies have focused on the central region of the system, with ∼80 per cent of the known members enclosed within 1 r h and 94 per cent within 2 r h to maximize the chance of finding member stars, since there should be 50 per cent of stars within 1 r h and 85 per cent within 2 r h when an exponential radial profile is considered.…”