论文标题
银河系可能涉及的蓝色 - 哈洛星星的底部重量初始质量功能
A bottom-heavy initial mass function for the likely-accreted blue-halo stars of the Milky Way
论文作者
论文摘要
我们使用GAIA DR2在250 pc内测量恒星的初始质量功能（IMF），质量在0.2 <m/msun <1.0范围内，根据运动学和金属性分离，根据Gaia横向速度，V_T和Hertzsprung-Russell-Russell-Russell Dagram（HRD）的位置确定。 The predominant thin-disc population (v_T < 40 km/s) has an IMF similar to traditional (e.g. Kroupa 2001}) stellar IMFs, with star numbers per mass interval dN/dm described by a broken power law, m^(-alpha), and index alpha_high=2.03 +0.14/-0.05 above m~0.5, shallowing to alpha_low=1.34 +0.11/-0.22在m〜 <0.5时。厚碟星（60 km/s <v_t <150 km/s）和属于“高金属性”或“红色序列” halo（v_t> 100 km/s或v_t> 200 km/s），并位于Hrd等于HRD的高于金属性[m/h]> -0.6）上的hrd splope a spligh and spligh and sl. 3. +0.97/-0.19（和类似的低质量斜率alpha_low = 1.14 +0.42/-0.50）。然而，来自“蓝色序列”的光环恒星的特征是低金属性（[m/h] <-0.6），但是，在大多数质量范围内，由单个功率定律具有独特的，底部丰富的IMF，由单个功率定律（alpha = 1.82 +0.17/-0.14）很好地描述。低金属性光环的IMF让人联想到已经在巨大的早期型星系中衡量的类似Salpeter的IMF，这是一种恒星种群，像乳白色的光晕恒星一样，它具有较高的α元素与铁的比例，[Alpha/fe]。蓝色序列的恒星可能是大约10 Gyrs of Gaia-cenceladus矮星银河系或类似事件的大约10 Gyrs的碎片。这些结果暗示了两个古老的恒星种群共有的恒星形成模式 - 椭圆星系和星系可能是我们的早期积聚的。
We use Gaia DR2 to measure the initial mass function (IMF) of stars within 250 pc and masses in the range 0.2 < m/Msun < 1.0, separated according to kinematics and metallicity, as determined from Gaia transverse velocity, v_T, and location on the Hertzsprung-Russell diagram (HRD). The predominant thin-disc population (v_T < 40 km/s) has an IMF similar to traditional (e.g. Kroupa 2001}) stellar IMFs, with star numbers per mass interval dN/dm described by a broken power law, m^(-alpha), and index alpha_high=2.03 +0.14/-0.05 above m~0.5, shallowing to alpha_low=1.34 +0.11/-0.22 at m~<0.5. Thick-disc stars (60 km/s < v_T < 150 km/s) and stars belonging to the "high-metallicity" or "red-sequence" halo (v_T > 100 km/s or v_T > 200 km/s, and located above the isochrone on the HRD with metallicity [M/H] > -0.6) have a somewhat steeper high-mass slope, alpha_high=2.35 +0.97/-0.19 (and a similar low-mass slope alpha_low=1.14 +0.42/-0.50). Halo stars from the "blue sequence", which are characterised by low-metallicity ([M/H] < -0.6), however, have a distinct, bottom-heavy IMF, well-described by a single power law with alpha=1.82 +0.17/-0.14 over most of the mass range probed. The IMF of the low-metallicity halo is reminiscent of the Salpeter-like IMF that has been measured in massive early-type galaxies, a stellar population that, like Milky-Way halo stars, has a high ratio of alpha elements to iron, [alpha/Fe]. Blue-sequence stars are likely the debris from accretion by the Milky Way, ~10 Gyrs ago, of the Gaia-Enceladus dwarf galaxy, or similar events. These results hint at a distinct mode of star formation common to two ancient stellar populations -- elliptical galaxies and galaxies possibly accreted early-on by ours.
