The Pristine Dwarf-Galaxy survey — IV. Probing the outskirts of the dwarf galaxy Bo”otes I. (arXiv:2107.10849v3 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Longeard_N/0/1/0/all/0/1">Nicolas Longeard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jablonka_P/0/1/0/all/0/1">Pascale Jablonka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Arentsen_A/0/1/0/all/0/1">Anke Arentsen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Thomas_G/0/1/0/all/0/1">Guillaume F. Thomas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aguado_D/0/1/0/all/0/1">David S. Aguado</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Carlberg_R/0/1/0/all/0/1">Raymond G. Carlberg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lucchesi_R/0/1/0/all/0/1">Romain Lucchesi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Malhan_K/0/1/0/all/0/1">Khyati Malhan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Martin_N/0/1/0/all/0/1">Nicolas Martin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+McConnachie_A/0/1/0/all/0/1">Alan W. McConnachie</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Navarro_J/0/1/0/all/0/1">Julio F. Navarro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanchez_Janssen_R/0/1/0/all/0/1">Rub&#xe9;n S&#xe1;nchez-Janssen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sestito_F/0/1/0/all/0/1">Federico Sestito</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Starkenburg_E/0/1/0/all/0/1">Else Starkenburg</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Yuan_Z/0/1/0/all/0/1">Zhen Yuan</a>

We present a new spectroscopic study of the dwarf galaxy Bootes I (Boo I)
with data from the Anglo-Australian Telescope and its AAOmega spectrograph
together with the Two Degree Field multi-object system. We observed 36
high-probability Boo I stars selected using Gaia Early Data Release 3 proper
motions and photometric metallicities from the Pristine survey. Out of those,
27 are found to be Boo I’s stars, resulting in an excellent success rate of 75%
at finding new members. Our analysis uses a new pipeline developed to estimate
radial velocities and equivalent widths of the calcium triplet lines from
Gaussian and Voigt line profile fits. The metallicities of 16 members are
derived, including 3 extremely metal-poor stars ([Fe/H] < -3.0), which
translates into a success rate of 25% at finding them with the combination of
Pristine and Gaia. Using the large spatial extent of our new members that spans
up to 4.1 half-light radii and spectroscopy from the literature, we find a
systemic velocity gradient of 0.40 +/- 0.10 km/s/arcmin and a small but
resolved metallicity gradient of -0.008 +/- 0.003 dex/arcmin. Finally, we show
that Boo I is more elongated than previously thought with an ellipticity of
epsilon = 0.68 +/- 0.15. Its velocity and metallicity gradients as well as its
elongation suggest that Boo I may have been affected by tides, a result
supported by direct dynamical modelling.

We present a new spectroscopic study of the dwarf galaxy Bootes I (Boo I)
with data from the Anglo-Australian Telescope and its AAOmega spectrograph
together with the Two Degree Field multi-object system. We observed 36
high-probability Boo I stars selected using Gaia Early Data Release 3 proper
motions and photometric metallicities from the Pristine survey. Out of those,
27 are found to be Boo I’s stars, resulting in an excellent success rate of 75%
at finding new members. Our analysis uses a new pipeline developed to estimate
radial velocities and equivalent widths of the calcium triplet lines from
Gaussian and Voigt line profile fits. The metallicities of 16 members are
derived, including 3 extremely metal-poor stars ([Fe/H] < -3.0), which
translates into a success rate of 25% at finding them with the combination of
Pristine and Gaia. Using the large spatial extent of our new members that spans
up to 4.1 half-light radii and spectroscopy from the literature, we find a
systemic velocity gradient of 0.40 +/- 0.10 km/s/arcmin and a small but
resolved metallicity gradient of -0.008 +/- 0.003 dex/arcmin. Finally, we show
that Boo I is more elongated than previously thought with an ellipticity of
epsilon = 0.68 +/- 0.15. Its velocity and metallicity gradients as well as its
elongation suggest that Boo I may have been affected by tides, a result
supported by direct dynamical modelling.

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