The Chemical Enrichment History of the Large Magellanic Cloud

Abstract

Ca II triplet spectroscopy has been used to derive stellar metallicities for individual stars in four LMC fields situated at galactocentric distances of 3 • , 5 • , 6 • -2and 8 • to the north of the Bar. Observed metallicity distributions show a well defined peak, with a tail toward low metallicities. The mean metallicity remains constant until 6 • ([Fe/H]∼-0.5 dex), while for the outermost field, at 8 • , the mean metallicity is substantially lower than in the rest of the disk ([Fe/H]∼-0.8 dex). The combination of spectroscopy with deep CCD photometry has allowed us to break the RGB age-metallicity degeneracy and compute the ages for the objects observed spectroscopically. The obtained age-metallicity relationships for our four fields are statistically indistinguishable. We conclude that the lower mean metallicity in the outermost field is a consequence of it having a lower fraction of intermediate-age stars, which are more metal-rich than the older stars. The disk age-metallicity relationship is similar to that for clusters. However, the lack of objects with ages between 3 and 10 Gyr is not observed in the field population. Finally, we used data from the literature to derive consistently the age-metallicity relationship of the bar. Simple chemical evolution models have been used to reproduce the observed age-metallicity relationships with the purpose of investigating which mechanism has participated in the evolution of the disk and bar. We find that while the disk age-metallicity relationship is well reproduced by close-box models or models with a small degree of outflow, that of the bar is only reproduced by models with combination of infall and outflow.

The metallicity gradient as a tracer of history and structure: the Magellanic Clouds and M33 galaxies

“…The bar, residing in the disc (Zaritsky et al 1994), is usually referred to as a separate component and can considerably reduce pre-existing abundance gradients over a few dynamical timescales since its formation (Friedli & Benz 1995). (2008) and Carrera et al (2008a) original data and the values resulting from applying a correction for the difference between Ca II triplet abundances and abundances obtained directly from iron lines (Appendix A). The latter are used in this study.…”

“…If many of the AGB stars analysed here are older than the bulk of RGB stars, they will more closely follow the outer disc/halo. (2008) and Carrera et al (2008a) in the field (light blue) as from Table 2, Grocholski et al (2006Grocholski et al ( , 2007 for stellar clusters (with small error bars; dark blue) and Borissova et al (2006) for RR Lyrae stars (without error bars; green), see text for details. The colour figure is available electronically.…”

New Spectroscopic Technique Based on Coaddition of Surface Brightness Fluctuations: NGC 4449 and Its Stellar Tidal Stream

“…For comparison, we show the metallicity measurements for the dwarf galaxies in the Local Group available in the literature. The two black squares indicate the Large and Small Magellanic Clouds (LMC, SMC; Carrera et al 2008aCarrera et al , 2008b. The black triangles indicate the Milky Way dSphs (Kirby et al 2011).…”

“…We use as reference the average metallicity based on individual RGB stars for MW dSphs, M31 faint dSphs, and M31 bright dSphs, dEs, and M32 (Kirby et al 2011;Collins et al 2013;Ho et al 2015, respectively). We also include the average stellar metallicity values for the Large and Small Magellanic Clouds (LMC, SMC; Carrera et al 2008aCarrera et al , 2008b and the Sagittarius stream (Mateo 1998). The metallicity we obtain by using this new technique for the stellar stream follows the metallicity-luminosity relation of dwarf galaxies in the Local Group.…”

The Ca ii triplet in red giant spectra: [Fe/H] determinations and the role of [Ca/Fe]

“…These include Galactic globular clusters (e.g., Armandroff & Da Costa 1991;Da Costa & Armandroff 1995;Rutledge et al 1997;Saviane et al 2012), Galactic open clusters (e.g., Cole et al 2004;Warren & Cole 2009;Carretta et al 2009;Carrera et al 2015) and stars in the Galactic Bulge (e.g., Vásquez et al 2015). It has also been used to study both field stars and star clusters in the LMC (e.g., Olszewski et al 1991;Cole et al 2005;Carrera et al 2008a) and SMC (e.g., Da Costa & Hatzidimitriou 1998;Carrera et al 2008b;Parisi et al 2010;Dobbie et al 2014;Parisi et al 2015), as well as red giants in dwarf spheroidal (e.g., Armandroff & Da Costa 1991;Pont et al 2004;Tolstoy et al 2004;Battaglia et al 2008Battaglia et al , 2011 and dwarf irregular galaxies (e.g., Leaman et al 2013). …”