Chemical Signature of a Major Merger in the Early Formation of Small Magellanic Cloud

Abstract

The formation history of the Small Magellanic cloud (SMC) is unraveled based on the results of our new chemical evolution models constructed for the SMC, highlighting the observed anomaly in the age-metallicity relation for star clusters in the SMC. We first propose that evidence of a major merger is imprinted in the age-metallicity relation as a dip in [Fe/H]. Our models predict that the major merger with a mass ratio of 1:1 to 1:4 occurred at ~7.5 Gyr ago, with a good reproduction of the abundance distribution function of field stars in the SMC. Furthermore, our models predict a relatively large scatter in [Mg/Fe] for -1.4 < [Fe/H] <-1.1 as a reflection of a looping feature resulting from the temporally inverse progress of chemical enrichment, which can be tested against future observational results. Given that the observed velocity dispersion (~30 km/s) of the SMC is much smaller than that (~160 km/s) of the Galactic halo, our finding strongly implies that the predicted merger event happened in a small group environment that was far from the Galaxy and contained a number of small gas-rich dwarfs comparable to the SMC. This theoretical view is extensively discussed in the framework that considers a connection with the formation history of the Large Magellanic cloud.

5 pages including 4 figures, to appear in ApJ Letters

References in corpus (9)

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Cited by in corpus (15)

• The VMC Survey - XIV. First results on the look-back time star-formation rate tomography of the Small Magellanic Cloud
• The synchronised dance of the Magellanic Clouds' star formation history
• Red Giants in the Small Magellanic Cloud. II. Metallicity Gradient and Age-Metallicity Relation
• Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. III. Abundances and Velocities for a Sample of 14 Clusters
• The VISCACHA survey -- IV. The SMC West Halo in 8D
• The chemical DNA of the Magellanic Clouds -- I. The chemical composition of 206 Small Magellanic Cloud red giant stars
• Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. V. Abundances and Velocities for 12 Massive Clusters
• Metallicities and ages for 35 star clusters and their surrounding fields in the Small Magellanic Cloud
• The VISCACHA survey -- VII. Assembly history of the Magellanic Bridge and SMC Wing from star clusters
• Ca II Triplet Spectroscopy of Small Magellanic Cloud Red Giants. VI. Analysis of chemical properties of the Main Body
• A genuine Large Magellanic Cloud age gap star cluster
• The VISCACHA survey -- VIII. Chemical evolution history of Small Magellanic Cloud West Halo cluster
• Astrophysical properties of newly discovered Magellanic Cloud star clusters
• Ages and metallicities of stellar clusters using S-PLUS narrow-band integrated photometry: the Small Magellanic Cloud
• The chemical DNA of the Magellanic Clouds VI. Origin and evolution of neutron-capture elements in the SMC