The S2 stream: the shreds of a primitive dwarf galaxy

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Aguado, David S. ^[1] ; Myeong, G. C. ^{[2, 1]} ; Belokurov, Vasily ^[1] ; Evans, N. Wyn ^[1] ; Koposov, Sergey E. ^{[1, 3, 4]} ; Allende Prieto, Carlos ^{[5, 6]} ; Lanfranchi, Gustavo A. ^[7] ; Matteucci, Francesca ^{[8, 9, 10]} ; Shetrone, Matthew ^[11] ; Sbordone, Luca ^[12] ; Navarrete, Camila ^{[13, 12]} ; Gonzalez Hernandez, I, Jonay ; Chaname, Julio ^{[14, 13]} ; de Arriba, Luis Peralta ^[1] ; Yuan, Zhen ^[15]

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^[1] Univ Cambridge, Inst Astron, Madingley Rd, Cambridge CB3 0HA - England

^[2] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 - USA

^[3] Univ Edinburgh, Inst Astron, Royal Observ, Blackford Hill, Edinburgh EH9 3HJ, Midlothian - Scotland

^[4] Carnegie Mellon Univ, McWilliams Ctr Cosmol, Pittsburgh, PA 15213 - USA

^[5] I, Inst Astrofis Canarias, Via Lactea, E-38205 Tenerife - Spain

^[6] I, Univ La Laguna, Dept Astrofis, E-38206 Tenerife - Spain

^[7] Univ Cidade Sao Paulo, Nucleo Astrofis Teor, R Galvao Bueno 868, BR-01506000 Sao Paulo, SP - Brazil

^[8] Univ Trieste, Sez Astron, Dipartimento Fis, Via GB Tiepolo 11, I-34131 Trieste - Italy

^[9] INAF Osservatorio Astron Trieste, Via GB Tiepolo 11, I-34131 Trieste - Italy

^[10] Ist Nazl Fis Nucl, Sez Trieste, Via Valerio 2, I-34134 Trieste - Italy

^[11] Univ Calif Santa Cruz, Univ Calif Observ, Santa Cruz, CA 95064 - USA

^[12] European Southern Observ, ESO, Alonso Cordova 3107, Santiago - Chile

^[13] Millennium Inst Astrophys, Av Vicuna Mackenna 4860, Santiago 7820436 - Chile

^[14] Pontificia Univ Catolica Chile, Inst Astrofis, Av Vicuna Mackenna 4860, Santiago 7820436 - Chile

^[15] Shanghai Astron Observ, Key Lab Res Galaxies & Cosmol, 80 Nandan Rd, Shanghai 200030 - Peoples R China

• Tipo de documento: Artigo Científico
• Fonte: Monthly Notices of the Royal Astronomical Society; v. 500, n. 1, p. 889-910, JAN 2021.
• Citações Web of Science: 1

Resumo

The S2 stream is a kinematically cold stream that is plunging downwards through the Galactic disc. It may be part of a hotter and more diffuse structure called the Helmi stream. We present a multi-instrument chemical analysis of the stars in the metal-poor S2 stream using both high- and low-resolution spectroscopy, complemented with a re-analysis of the archival data to give a total sample of 62 S2 members. Our high-resolution program provides alpha-elements (C, Mg, Si, Ca, and Ti), iron-peak elements (V, Cr, Mn, Fe, Ni), n-capture process elements (Sr, Ba), and other elements such as Li, Na, Al, and Sc for a subsample of S2 objects. We report coherent abundance patterns over a large metallicity spread (similar to 1 dex) confirming that the S2 stream was produced by a disrupted dwarf galaxy. The combination of S2's alpha-elements displays a mildly decreasing trend with increasing metallicity, which can be tentatively interpreted as a `knee' at {[}Fe/H] < -2. At the low-metallicity end, the n-capture elements in S2 may be dominated by r-process production; however, several stars are Ba-enhanced but unusually poor in Sr. Moreover, some of the low-{[}Fe/H] stars appear to be carbon-enhanced. We interpret the observed abundance patterns with the help of chemical evolution models that demonstrate the need for modest star formation efficiency and low wind efficiency confirming that the progenitor of S2 was a primitive dwarf galaxy. (AU)

• Processo FAPESP: 14/11156-4 - O que determina o crescimento da massa estelar de galáxias elípticas? Intrínseco ou ambiente: a saga contínua
• Beneficiário: Reinaldo Ramos de Carvalho
• Linha de fomento: Auxílio à Pesquisa - Temático
• Processo FAPESP: 17/25799-2 - Galáxias Anãs Locais: Dinâmica Interna e Enriquecimento Químico
• Beneficiário: Gustavo Amaral Lanfranchi
• Linha de fomento: Auxílio à Pesquisa - Regular