在低表面亮度球状星团-富矮星系中“所有地方的一切同时”形成的迹象
Signs of `Everything Everywhere All At Once' formation in low surface brightness globular cluster-rich dwarf galaxies
摘要：
只有两个超扩散星系（UDG）的空间分辨恒星星族的属性，都表现出径向平坦上升的金属丰度配置文件，表明不同的形成途径，以大多数矮星系。缺乏其他低表面亮度（LSB）的矮星进行类似的分析，阻碍了对这种行为的深入理解。我们研究了在“极端星系分析”（AGATE）合作中新观察到的四个富含球状星团（GC）的LSB矮星的年龄、金属丰度和恒星形成历史的径向轮廓。DFX 1和DF 07是真正的UDG，而PUDG-R27和VCC 1448几乎是UDG（NUDG）。将他们和DF 44的结果与模拟结果进行比较，我们的目标是揭示它们的形成途径。我们使用pPXF拟合不同的光谱提取的环形孔径恢复恒星星族的性质和计算它们的梯度。我们比较了文献经典矮星和模拟的样本，特别是与模拟的UDG。我们的五个LSB矮星呈现出平坦的年龄和平坦到上升的金属丰度轮廓。平坦的年龄梯度与经典矮星的年龄梯度（观测到的和宇宙学模拟的）一致，但金属丰度梯度不同。我们所有的LSB矮星（除了PUDG-R27，显示出明显的金属丰度增加的轮廓）都与年龄-金属丰度梯度关系的极端尾部相一致，倾向于同时形成星系。这个富含GC的LSB矮星样本具有空间分辨特性，证实它们似乎遵循与经典矮星不同的形成路径。然而，更大的样本，更高的S/N光谱和不同数量的GC丰富的LSB矮星系的形成路径上设置强大的约束。
英文摘要：
Only two ultra-diffuse galaxies (UDGs) have spatially resolved stellar population properties, both showing radially flat-to-rising metallicity profiles, indicative of a different formation pathway to most dwarf galaxies. The scarcity of other low surface brightness (LSB) dwarfs with a similar analysis prevents a deeper understanding on this behaviour. We investigate the radial profiles of the ages, metallicities and star formation histories of four globular cluster (GC) rich LSB dwarfs, newly observed within the 'Analysis of Galaxies At The Extremes' (AGATE) collaboration. DFX1 and DF07 are bona-fide UDGs, while PUDG-R27 and VCC1448 are nearly UDGs (NUDGes). Comparing their and DF44's results to simulations, we aim to reveal their formation pathways. We use pPXF to fit different spectra extracted in annular apertures to recover the stellar population properties and compute their gradients. We compare those with a sample of literature classical dwarfs and simulations, in particular with simulated UDGs. Our five LSB dwarfs present flat age and flat-to-rising metallicity profiles. The flat age gradients are compatible with those of classical dwarfs (both observed and from cosmological simulations), but the metallicity gradient diverges. All of our LSB dwarfs (except for PUDG-R27, showing a pronounced increasing metallicity profile) are compatible with being the extreme tail of the age-metallicity gradient relation, with a preference to co-eval formation forming the galaxy all at once. This sample of GC-rich LSB dwarfs with spatially resolved properties confirms that they seem to follow a different formation path than classical dwarfs. However, larger samples with higher S/N spectra and varying amounts of GC richness are required to set robust constraints on the formation pathways of LSB dwarf galaxies.
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