论文标题
图卡纳II超品种矮人银河系郊区恒星的详细化学丰度
Detailed chemical abundances of stars in the outskirts of the Tucana II ultra-faint dwarf galaxy
论文作者
论文摘要
我们从高分辨率麦哲伦/麦克光谱学中的图卡纳II超生物星系中心（UFD）介绍了五颗星在0.3 kpc至1.1 kpc之间的五颗星的化学丰度和速度。我们发现，每个恒星都缺乏金属（-3.6 <[fe/h] <-1.9）和中子捕获元素，这是UFD恒星的特征，明确地证实了他们与图卡纳II的关联。其他化学丰度（例如，C，铁峰）在很大程度上遵循UFD趋势，并表明微弱的核心折叠超新星（SNE）主导了图卡纳II的早期演变。我们在[fe/h] $ \ \ -2.8 $上看到[$α$/fe]的低迷，这表明IA型Sn型富集的发作和某种程度上扩展的化学演化。最富含金属的恒星非常低[sc/fe] = $ -1.29 \ pm 0.48 $和[mn/fe] = $ -1.33 \ pm 0.33 $，这意味着Sub-Chandrasekhar质量质量IA SN具有显着的丰富。我们没有在图卡纳II（$ \ text {d} v _ {\ text {helio}}/\ text {d}θ_1= -2.6^{+3.0} _ {+3.0} _ { - 2.9} $ s $ s $ s $ s $ kpc $ kpc $ kpc $ kpc $ km km km km kpc a { - 1} a中，我们没有检测到图卡纳II中的径向速度梯度破坏，并得出$ m_ {1/2}（r_h）= 1.6^{+1.1} _ { - 0.7} \ times 10^6 $ m $ _ {\ odot} $的动态质量。根据其出色的化学丰度，我们重新审视图卡纳II扩展成分的形成场景。我们没有发现图卡纳II具有异常能量的SNE的证据，这表明如果SNE驱动原地恒星光环的形成，那么其他UFD也应显示出类似的此类特征。尽管不是独特的解释，但[$α$/fe]的下降与早期的银河合并触发后来的恒星形成是一致的。未来的观察结果可能会消除UFD郊区的这种形成渠道。
We present chemical abundances and velocities of five stars between 0.3 kpc to 1.1 kpc from the center of the Tucana II ultra-faint dwarf galaxy (UFD) from high-resolution Magellan/MIKE spectroscopy. We find that every star is deficient in metals (-3.6 < [Fe/H] < -1.9) and in neutron-capture elements as is characteristic of UFD stars, unambiguously confirming their association with Tucana II. Other chemical abundances (e.g., C, iron-peak) largely follow UFD trends and suggest that faint core-collapse supernovae (SNe) dominated the early evolution of Tucana II. We see a downturn in [$α$/Fe] at [Fe/H] $\approx -2.8$, indicating the onset of Type Ia SN enrichment and somewhat extended chemical evolution. The most metal-rich star has strikingly low [Sc/Fe] = $-1.29 \pm 0.48$ and [Mn/Fe] = $-1.33 \pm 0.33$, implying significant enrichment by a sub-Chandrasekhar mass Type Ia SN. We do not detect a radial velocity gradient in Tucana II ($\text{d}v_{\text{helio}}/\text{d}θ_1=-2.6^{+3.0}_{-2.9}$ km s$^{-1}$ kpc$^{-1}$) reflecting a lack of evidence for tidal disruption, and derive a dynamical mass of $M_{1/2} (r_h) = 1.6^{+1.1}_{-0.7}\times 10^6$ M$_{\odot}$. We revisit formation scenarios of the extended component of Tucana II in light of its stellar chemical abundances. We find no evidence that Tucana II had abnormally energetic SNe, suggesting that if SNe drove in-situ stellar halo formation then other UFDs should show similar such features. Although not a unique explanation, the decline in [$α$/Fe] is consistent with an early galactic merger triggering later star formation. Future observations may disentangle such formation channels of UFD outskirts.
