Pushing back the limits: detailed properties of dwarf galaxies in a ΛCDM universe

Abstract

We present the results of a set of high resolution chemo-dynamical simulations of dwarf galaxies in a ΛCDM cosmology. Out of an original (3.4 Mpc/h) 3 cosmological box, a sample of 27 systems are re-simulated from z=70 to z=0 using a zoom-in technique. Gas and stellar properties are confronted to the observations in the greatest details: in addition to the galaxy global properties, we investigated the model galaxy velocity dispersion profiles, half-light radii, star formation histories, stellar metallicity distributions, and [Mg/Fe] abundance ratios. The formation and sustainability of the metallicity gradients and kinematically distinct stellar populations are also tackled. We show how the properties of six Local Group dwarf galaxies, NGC 6622, Andromeda II, Sculptor, Sextans, Ursa Minor and Draco are reproduced, and how they pertain to three main galaxy build-up modes. Our results indicate that the interaction with a massive central galaxy could be needed for a handful of Local Group dwarf spheroidal galaxies only, the vast majority of the systems and their variety of star formation histories arising naturally from a ΛCDM framework. We find that models fitting well the local Group dwarf galaxies are embedded in dark haloes of mass between 5 × 10 8 to a few 10 9 M , without any missing satellite problem. We confirm the failure of the abundance matching approach at the mass scale of dwarf galaxies. Some of the observed faint however gas-rich galaxies with residual star formation, such as Leo T and Leo P, remain challenging. They point out the need of a better understanding of the UV-background heating.

The Tucana dwarf spheroidal galaxy: not such a massive failure after all

“…Our best value for the velocity dispersion of σ v = 6.2 +1.6 −1.3 km s −1 is significantly lower (∼3-σ) than what reported in the literature by both F09 and G19 (see also the discussion in the previous section), but closer now to the values observed for other similarly luminous dwarf galaxies of the Local Group (see e.g. Kirby et al 2014;Revaz & Jablonka 2018).…”

“…These results have also been reproduced by simulations (e.g. Schroyen et al 2013;Revaz & Jablonka 2018), which have shown that the shape of these gradients strongly depends on the combination of the stellar mass, SFH and dynamical history of the system under consideration, although their strength could be influenced by merger events (Benítez-Llambay et al 2016) or environmental effects such as tidal stripping (Sales et al 2010).…”

“…The presence of a gradient in Tucana would be expected from the age gradients inferred from deep photometric studies (Hidalgo et al 2013;Savino et al 2019), but also from both observations and simulations of similarly luminous dwarfs (see e.g. Leaman et al 2013;Schroyen et al 2013;Revaz & Jablonka 2018), which indeed host mild metallicity gradients. Therefore, the presence of an underling gradient in Tucana is not excluded, but it would need a better sampling of the metal-poor component in Tucana (particularly at R 3R e ) to confirm it.…”

“…Sextans). It has been shown that such short SFHs may lead to mild metallicity gradients in these systems (Marcolini et al 2008;Kirby et al 2011;Revaz & Jablonka 2018). Indeed, both Draco and Ursa Minor show mild gradients having values of −0.05 dex R −1 e and −0.03 dex R −1 e , as reported by Schroyen et al (2013) and Kirby et al (2011), respectively 7 .…”

“…Internal effects, like stellar feedback due to episodic star formation and supernova-driven winds, play an important role too (see e.g. Sawala et al 2010;Bermejo-Climent et al 2018;Revaz & Jablonka 2018 A&A proofs: manuscript no. tucana_arxiv to reproduce the observed properties of the LG dwarf galaxies (see e.g.…”