A1 Refereed original research article in a scientific journal
Looking into the faintEst WIth MUSE (LEWIS): Exploring the nature of ultra-diffuse galaxies in the Hydra-I cluster: V. Integrated stellar population properties
Authors: Doll, Goran; Buttitta, Chiara; Iodice, Enrichetta; Ferré-Mateu, Anna; Falcón-Barroso, Jesus; Martín-Navarro, Ignacio; Paolillo, Maurizio; Rossi, Luca; Forbes, Duncan A.; Spiniello, Chiara; Hartke, Johanna; Gullieuszik, Marco; Arnaboldi, Magda; Cantiello, Michele; Corsini, Enrico Maria; D'Ago, Giuseppe; Hilker, Michael; La Marca, Antonio; Mieske, Steffen; Mirabile, Marco; Rejkuba, Marina; Spavone, Marilena
Publisher: EDP Sciences
Publication year: 2026
Journal: Astronomy and Astrophysics
Article number: A88
Volume: 707
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202556736
Publication's open availability at the time of reporting: Open Access
Publication channel's open availability : Open Access publication channel
Web address : https://doi.org/10.1051/0004-6361/202556736
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/523410740
Self-archived copy's licence: CC BY
Self-archived copy's version: Publisher`s PDF
Context. This paper presents new results from the ESO Large Programme Looking into the faintEst WIth MUSE (LEWIS). The LEWIS sample consists of low-surface-brightness galaxies (LSBs) and ultra-diffuse galaxies (UDGs) located inside 0.4Rvir of the Hydra I cluster. Integral-field spectroscopy is acquired for 24 galaxies with the MUSE spectrograph mounted on the Very Large Telescope (VLT).
Aims. Our main objectives are to analyse possible correlations between the environment and the integrated stellar population properties of our targets, based on which we infer clues about their formation.
Methods. For each galaxy in the sample, we extracted the 1D stacked spectrum in an aperture of one effective radius Re and adopted previously published stellar kinematics to derive the age, metallicity, and [Mg/Fe] through a full spectral fitting technique.
Results. We find that the analysed LEWIS sample has a mean metallicity of ⟨[M/H]⟩= − 0.9 ± 0.2 dex and a mean age of 10 ± 2 Gyr, comparable to previous results of UDGs in other clusters. According to their position in the projected phase space, galaxies can be classified into two groups: very early infaller galaxies, which on average have slightly higher metallicities (⟨[M/H]⟩early = −0.8 ± 0.1 dex), and late infaller galaxies, with slightly lower values (⟨[M/H]⟩late = −1.0 ± 0.1 dex). According to their properties, late-infallers tend to be rotation-supported systems. Conversely, two types of galaxies are found in the early-infall region. Roughly half have metallicities consistent with the dwarf galaxy mass–metallicity relation. The other half show higher metallicities (with ⟨[M/H]⟩≥ − 1.0 dex) and are located outside the 1σ scatter of the mass-metallicity relation. The two subgroups of early-infallers also display different timescales for stellar mass assembly. Metal-rich galaxies reached 50% of their stellar mass in less than 1 Gyr and show a prolonged and almost constant star formation over more than 12 Gyr. The other galaxies exhibit a star formation history similar to that found for galaxies in the late-infall region. Both early and late infallers show solar-like α abundances.
Conclusions. From the analysis of stellar population properties presented in this work and of stellar kinematics previously obtained from LEWIS, we identified different classes of UDGs within the Hydra I cluster – as shown by metallicities, quenching timescales, and kinematics – which suggest different formation mechanisms. Almost all of the UDGs and LSBs in this cluster are consistent with the puffed-up dwarf formation scenario, having dwarf-like metallicities and being consistent with the mass-metallicity relation for dwarfs. In the innermost regions of the cluster, where more metal-rich UDGs are found, tidal effects or the environment might have influenced their formation and evolution.
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We wish to thank the anonymous Referee whose comments helped us to improve the clarity of the manuscript. Based on observations collected at the European Southern Observatory under ESO programmes 108.222P.001, 108.222P.002, 108.222P.003. The authors wish to thank the Instituto de Astrofísica de Canarias for their hospitality and mentorship during January to April. Additionally, we are grateful to Jonah Gannon, Maria Luisa Buzzo, Thomas Puzia, and Alexandre Vazdekis for their helpful discussions and valuable suggestions. E.I. acknowledges support by the INAF GO funding grant 2022-2023. EI, EMC and MP acknowledge the support by the Italian Ministry for Education University and Research (MIUR) grant PRIN 2022 2022383WFT “SUNRISE”, CUP C53D23000850006. EMC acknowledges the support from MIUR grant PRIN 2017 20173ML3WW-001 and Padua University grants DOR 2021-2023. GD acknowledges support by UKRI-STFC grants: ST/T003081/1 and ST/X001857/1. A.F.M. has received support from RYC2021-031099-I and PID2021-123313NA-I00 of MICIN/AEI/10.13039/501100011033/FEDER,UE, NextGenerationEU/PRT DF thanks the ARC for support via DP220101863 and DP200102574. J.F-B acknowledges support from the PID2022-140869NB-I00 grant from the Spanish Ministry of Science and Innovation. J.H. and E.I. acknowledge the financial support from the Visitor and Mobility program of the Finnish Centre for Astronomy with ESO (FINCA). This work is based on the funding from the INAF through the GO large grant in 2022, to support the LEWIS data reduction and analysis (PI E. Iodice). The authors thank Gannon et al. (2024) for the compilation of their catalogue of UDG spectroscopic properties. The catalogue includes data from: McConnachie (2012), van Dokkum et al. (2015), Beasley & Trujillo (2016), Martin et al. (2016), Yagi et al. (2016), Martínez-Delgado et al. (2016), van Dokkum et al. (2016, 2017), Karachentsev et al. (2017), van Dokkum et al. (2018), Toloba et al. (2018), Gu et al. (2018), Lim et al. (2018), Ruiz-Lara et al. (2018), Alabi et al. (2018), Ferré-Mateu et al. (2018), Forbes et al. (2018), Martin et al. (2019), Chilingarian et al. (2019), Fensch et al. (2019), Danieli et al. (2019), van Dokkum et al. (2019), Torrealba et al. (2019), Iodice et al. (2020), Collins et al. (2020), Müller et al. (2020), Gannon et al. (2020), Lim et al. (2020), Müller et al. (2021), Forbes et al. (2021), Shen et al. (2021), Ji et al. (2021), Huang & Koposov (2021), Gannon et al. (2021, 2022), Mihos et al. (2022), Danieli et al. (2022), Villaume et al. (2022), Webb et al. (2022), Saifollahi et al. (2022), Janssens et al. (2022), Gannon et al. (2023), Ferré-Mateu et al. (2023), Toloba et al. (2023), Shen et al. (2023). The authors acknowledge the use of the following Python scripts: ASTROPY (Astropy Collaboration 2013, 2018), MATPLOTLIB (Hunter 2007), MPDAF (Bacon et al. 2016; Piqueras et al. 2017), NUMPY (van der Walt et al. 2011), PHOTUTILS (Bradley et al. 2023), SCIPY (Virtanen et al. 2020), and ZAP (Soto et al. 2016).
