Chemical history of isolated dwarf galaxies of the Local Group – I. dSphs: Cetus and Tucana

Abstract

For the first time, we obtain chemical evolution models (CEMs) for Tucana and Cetus, two isolated dwarf spheroidal galaxies (dSphs) of the Local Group. The CEMs have been built from the star formation histories (SFHs) and the metallicity histories, both obtained independently by the LCID project from deep color-magnitude diagrams. Based on our models, we find that the chemical histories were complex and can be divided into different epochs and scenarios. In particular, during 75% of the SFH, the galaxies behaved as closed boxes and, during the remaining 25%, either received a lot of primordial gas by accretion or they lost metals through metal-rich winds. In order to discriminate between these two scenarios, abundances ratios in old stars are needed. At t∼4.5 Gyr, the galaxies lost most of their gas due to a shortstrong, well-mixed wind. We obtain very similar CEMs for both galaxies, although Cetus is twice as massive as Tucana. We conclude that the star formation in both galaxies began with only 1.5% of the baryonic mass fraction predicted by ΛCDM.

Kinematics of the Tucana Dwarf Galaxy: an unusually dense dwarf in the Local Group

“…Gallart et al (2015) confirm that 90% of Tucana's stars formed more than 10 Gyr ago. Avila-Vergara et al (2016) find that 75% of Tucana's history has been spent as a 'closed box' with no net inflow or outflow of gas. A similar chemical history was also inferred for Cetus (Avila-Vergara et al 2016).…”

“…Avila-Vergara et al (2016) find that 75% of Tucana's history has been spent as a 'closed box' with no net inflow or outflow of gas. A similar chemical history was also inferred for Cetus (Avila-Vergara et al 2016). It has been proposed that the purported interaction between Tucana and the Milky Way some 10 Gyr ago could have stripped enough gas to completely shut down star formation in the galaxy (Teyssier et al 2012).…”

Exploring simulated early star formation in the context of the ultrafaint dwarf galaxies

“…Using simple yet powerful parameterizations, these models can trace the build up of iron and other elements as stars form within a galaxy of a given mass, creating tracks in abundance space that recreate what is seen in studies of Milky Way halo stars (McWilliam 1997). Whether purely analytic (Robertson et al 2005;Andrews et al 2017), coupled to an N-body simulation (Font et al 2006;Tumlinson 2010;Romano & Starkenburg 2013;Crosby et al 2016), or incorporating global, measured SFRs (Lanfranchi et al 2008;Avila-Vergara et al 2016), these models allow for quick variation of their parameters and for an assessment of the importance of a number of galaxy properties (e.g. inflows, outflows, SFH) in driving the chemical evolution of a given halo.…”