A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

XVIII. Reconstructing the star formation history of early-type galaxies through the combination of their UV and Hα emission

¹ Aix Marseille Université, CNRS, CNES, LAM, Marseille, France
² Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Mönchhofstraße 12-14, D-69120 Heidelberg, Germany
³ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius, Italy
⁴ Institute of Cosmology, University of Portsmouth, Burnaby Road, Portsmouth PO1 3FX, UK
⁵ Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, 06000 Nice, France
⁶ Università di Milano-Bicocca, Piazza della scienza 3, 20100 Milano, Italy
⁷ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20159 Milano, Italy
⁸ National Research Council of Canada, Herzberg Astronomy and Astrophysics Research Centre, Victoria, BC V9E 2E7, Canada
⁹ AIM, CEA, CNRS, Université Paris-Saclay, Université de Paris, 91191 Gif-sur-Yvette, France
¹⁰ Instituto de Astrofísica de Canarias, Vía Láctea S/N, E-38205 La Laguna, Spain
¹¹ Departamento de Astrofísica, Universidad de La Laguna, E-38206 La Laguna, Spain
¹² Waterloo Centre for Astrophysics, University of Waterloo, Waterloo, ON N2L 3G1, Canada
¹³ Department of Physics and Astronomy, University of Waterloo, Waterloo, ON N2L 3G1, Canada
¹⁴ Dept. of Physics and Astronomy, University of Calgary, Calgary AB T2N 1N4, Canada
¹⁵ Department of Physics and Astronomy, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
¹⁶ Indian Institute of Astrophysics, Bangalore, India
¹⁷ Department of Physics & Astronomy, University of Alabama in Huntsville, 3001 Sparkman Drive, Huntsville, AL 35899, USA
¹⁸ Department of Astronomy, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China

^⋆ Corresponding author; silvia.martocchia@lam.fr

Received: 14 November 2024
Accepted: 17 February 2025

Abstract

We reconstructed the star formation histories of seven massive (M_⋆ ≳ 10¹⁰ M_⊙) early-type galaxies (ETGs) in the Virgo cluster by analysing their spatially resolved stellar population (SP) properties including their ultraviolet (UV) and Hα emission. As part of the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE), we used Hα images to select ETGs that show no signs of ongoing star formation. We combined VESTIGE with images from Astrosat/UVIT, GALEX, and CFHT/MegaCam from the Next Generation Virgo Cluster Survey (NGVS) to analyse radial spectral energy distributions (SEDs) from the far-UV (FUV) to the near-infrared. The UV emission in these galaxies is likely due to old, low-mass stars in post main sequence (MS) phases, the so-called UV upturn. We fitted the radial SEDs with novel SP models that include an old, hot stellar component of post-MS stars with various temperatures and energetics (fuels). This way, we explored the main stellar parameters responsible for UV upturn stars regardless of their evolutionary path. We make these models publicly available through the SED fitting code CIGALE. Standard models are not able to reproduce the galaxies’ central FUV emission (SMA/R_eff ≲ 1), while the new models well characterise it through post-MS stars with temperatures T ≳ 25 000 K. All galaxies are old (mass-weighted ages ≳10 Gyr) and the most massive ones, M49 and M87, are supersolar (Z ≃ 2 Z_⊙) within their inner regions (SMA/R_eff ≲ 0.2). Overall, we find flat age gradients (∇Log(Age) ∼ −0.04 − 0 dex) and shallow metallicity gradients (∇Log(Z) < −0.2 dex), except for M87 (∇Log(Z_M87) ≃ −0.45 dex). Our results show that these ETGs formed with timescales τ ≲ 1500 Myr, having assembled between ∼40 − 90% of their stellar mass at z ∼ 5. This is consistent with recent JWST observations of quiescent massive galaxies at high-z, which are likely the ancestors of the largest ETGs in the nearby Universe. The derived flat and shallow stellar gradients indicate that major mergers might have contributed to the formation and evolution of these galaxies.