A 3D view of dwarf galaxies with Gaia and VLT/FLAMES

I. The Sculptor dwarf spheroidal^⋆,⋆⋆

¹ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
e-mail: etolstoy@astro.rug.nl
² Dipartimento di Fisica e Astronomia, Universitá degli Studi di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Italy
³ INAF/Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁴ Instituto de Astrofísica de Canarias, Calle Vía Láctea s/n, 38206 La Laguna, Tenerife, Spain
⁵ Universidad de La Laguna, Avda. Astrofísico Fco. Sánchez, 38205 La Laguna, Tenerife, Spain
⁶ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁷ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, 40129 Bologna, Italy
⁸ Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA UK
⁹ Laboratoire Lagrange, Université de Nice Sophia Antipolis, CNRS, Observatoire de la Côte d’Azur, CS34229 06304 Nice Cedex 4, France
¹⁰ Institute of Physics, Laboratory of Astrophysics, Ecole Polytechnique Fédérale de Lausanne (EPFL), Observatoire de Sauverny, 1290 Versoix, Switzerland
¹¹ GEPI, Observatoire de Paris, CNRS, Université Paris Diderot, 92125 Meudon Cedex, France
¹² Astrophysics Research Institute, Liverpool John Moores University, 146 Brownlow Hill, Liverpool, L3 5RF UK
¹³ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Received: 18 December 2022
Accepted: 14 April 2023

Abstract

We present a new homogeneous survey of VLT/FLAMES LR8 line-of-sight radial velocities (v_los) for 1604 resolved red giant branch stars in the Sculptor dwarf spheroidal galaxy. In addition, we provide reliable Ca II triplet metallicities, [Fe/H], for 1339 of these stars. From this combination of new observations (2257 individual spectra) with ESO archival data (2389 spectra), we obtain the largest and most complete sample of v_los and [Fe/H] measurements for individual stars in any dwarf galaxy. Our sample includes VLT/FLAMES LR8 spectra for ∼55% of the red giant branch stars at G < 20 from Gaia DR3, and > 70% of the brightest stars, G < 18.75. Our spectroscopic velocities are combined with Gaia DR3 proper motions and parallax measurements for a new and more precise membership analysis. We look again at the global characteristics of Sculptor, deriving a mean metallicity of ⟨[Fe/H]⟩ = −1.82 ± 0.45 and a mean line-of-sight velocity of ⟨v_los⟩ = + 111.2 ± 0.25 km s⁻¹. There is a clear metallicity gradient in Sculptor, −0.7deg dex⁻¹, with the most metal-rich population being the most centrally concentrated. Furthermore, the most metal-poor population in Sculptor, [Fe/H]<  − 2.5, appears to show kinematic properties distinct from the rest of the stellar population. Finally, we combine our results with the exquisite Gaia DR3 multi-colour photometry to further investigate the colour-magnitude diagram of the resolved stellar population in Sculptor. Our detailed analysis shows a similar global picture as previous studies, but with much more precise detail, revealing that Sculptor has more complex properties than previously thought. This survey emphasises the role of the stellar spectroscopy technique and this galaxy as a benchmark system for modelling galaxy formation and evolution on small scales.