The VISCACHA survey

VIII. Chemical evolution history of the Small Magellanic Cloud west halo clusters^⋆

¹ Instituto de Astrofísica, Facultad de Ciencias Exactas, Universidad Andrés Bello, Fernández Concha 700, 7591538 Las Condes, Santiago, Chile
e-mail: saroonsasi19@gmail.com
² Instituto de Alta Investigación, Sede Esmeralda, Universidad de Tarapacá, Chile
³ National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
⁴ Observatorio Astronómico, Universidad Nacional de Córdoba, Laprida 854, X5000BGR Córdoba, Argentina
⁵ Instituto de Astronomía Teórica y Experimental (CONICET-UNC), Laprida 854, X5000BGR Córdoba, Argentina
⁶ Instituto de Física – Universidade Federal do Rio de Janeiro, Av. Athos da Silveira Ramos, 149, Rio de Janeiro 21941-909, Brazil
⁷ Universidade Estadual de Santa Cruz (UESC), Departamento de Ciências Exatas, Rodovia Jorge Amado km 16, 45662-900 Ilhéus, Brazil
⁸ International Centre for Radio Astronomy Research, The University of Western Australia, 7 Fairway, Crawley, WA 6009, Australia
⁹ Vatican Observatory, V00120 Vatican City State, Italy
¹⁰ Departamento de Fisica, Universidade Federal de Santa Catarina, Trinidade, 88040-900 Florianopolis, Brazil
¹¹ Universidade de São Paulo, IAG, Rua do Matão 1226, Cidade Universitária, São Paulo 05508-900, Brazil
¹² Universidade Federal do ABC, Centro de Ciĉncias Naturais e Humanas, Avenida dos Estados, 5001 09210-580, Brazil
¹³ Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, CP 15051, Porto Alegre 91501-970, Brazil
¹⁴ Rubin Observatory Project Office, 950 N. Cherry Ave., Tucson, AZ 85719, USA
¹⁵ Laboratório Nacional de Astrofísica LNA/MCTI, 37504-364 Itajubá, MG, Brazil

Received: 13 April 2023
Accepted: 21 June 2023

Abstract

The chemical evolution history of the Small Magellanic Cloud (SMC) has been a matter of debate for decades. The challenges in understanding the SMC chemical evolution are related to a very slow star formation rate (SFR) combined with bursts triggered by the multiple interactions between the SMC and the Large Magellanic Cloud, a significant (∼0.5 dex) metallicity dispersion for the SMC cluster population younger than about 7.5 Gyr, and multiple chemical evolution models tracing very different paths through the observed age–metallicity relation of the SMC. There is no doubt that these processes were complex. Therefore, a step-by-step strategy is required in order to better understand the SMC chemical evolution. We adopted an existing framework to split the SMC into regions on the sky, and we focus on the west halo in this work, which contains the oldest and most metal-poor stellar populations and is moving away from the SMC, that is, in an opposite motion with respect to the Magellanic Bridge. We present a sample containing ∼60% of all west halo clusters to represent the region well, and we identify a clear age–metallicity relation with a tight dispersion that exhibits a 0.5 dex metallicity dip about 6 Gyr ago. We ran chemical evolution models and discuss possible scenarios to explain this metallicity dip, the most likely being a major merger accelerating the SFR after the event. This merger should be combined with inefficient internal gas mixing within the SMC and different SFRs in different SMC regions because the same metallicity dip is not seen in the AMR of the SMC combining clusters from all regions. We try to explain the scenario to better understand the SMC chemo-dynamical history.