We present a detailed analysis of the formation, evolution, and possible longevity of metallicity gradients in simulated dwarf galaxies. Specifically, we investigate the role of potentially orbit-changing processes such as radial stellar migration and dynamical heating in shaping or destroying these gradients. We also consider the influence of the star formation density threshold, investigating both a low and high value (0.1 amu/$cm^{3}$ - 100 amu/$cm^{3}$).
The Nbody-SPH models that we use to self-consistently form and evolve dwarf galaxies in isolation show that, in the absence of significant angular momentum, metallicity gradients are gradually built up during the evolution of the dwarf galaxy, by ever more centrally concentrated star formation adding to the overall gradient. Once formed, they are robust, survive easily in the absence of external disturbances and hardly decline over several Gyr, and they agree well with observed metallicity gradients of dwarf galaxies in the Local Group. The underlying orbital displacement of stars is quite limited in our models, being of the order of only fractions of the half light radius over time-spans of 5 to 10 Gyr in all star formation schemes. This is contrary to the strong radial migration found in massive disc galaxies, caused by scattering of stars off the corotation resonance of spiral structures. In the dwarf regime the stellar body only seems to undergo mild dynamical heating, due to the lack of long-lived spiral structures and/or discs.
The density threshold has profound influences on the star formation mode of the models, but only a minor influence on the evolution of metallicity gradients. Increasing the threshold 1000-fold causes comparatively stronger dynamical heating of the stellar body due to the increased turbulence and the scattering of stars off dense gas clouds, but the effect remains very limited in absolute terms.
HR-pyPopStar II: high spectral resolution evolutionary synthesis models low metallicity expansion and the properties of the stellar populations of dwarf galaxies
Max-Planck Institut für Astrophysik（马克斯·普朗克天体物理研究所）；Departamento de Investigación Básica, CIEMAT（基础研究部，CIEMAT）；Centro de Astrobiologí´a (CSIC/INTA)（天文生物学中心（CSIC/INTA））；FRACTAL S.L.N.E.
Metallicity Gradients - Mass Dependency in Dwarf Elliptical Galaxies
星系的形成和演化是由它们的恒星星族径向梯度决定的。最近的两篇文章提出了相互矛盾的结果，关于早期型矮星系的金属丰度梯度的质量依赖性。一方面，Spolaor等人表明总金属丰度、Z/H和质量之间存在紧密的正相关关系。另一方面，在不同的样品中，我们没有发现任何涉及Fe/H的趋势（Koleva等人）。为了调查的差异的起源，我们检查各种因素，可能会影响确定的梯度：即天空减法和信噪比。我们的结论是，我们的梯度检测远高于可能的分析偏差。然后，我们测量了Mg/Fe相对丰度分布，发现了中等梯度。导出的Z/H梯度分散在-0.4dex/re附近。这两个样本包含相同类型的对象，并且仍然不理解不一致的原因。根据ESO望远镜在La Silla Paranal天文台根据ID076.B-0196计划进行的观测。
