M31古老而沉重的隆起I.动能和恒星星族
The old and heavy bulge of M31 I. Kinematics and stellar populations
摘要：
我们提出了新的光学长缝数据沿6个位置角的隆起区的M31。我们推导出精确的恒星和气体运动学，距离中心5弧分，其中盘面光的贡献始终小于30%，沿着长轴达到8弧分，其中盘面占总光的55%。我们发现McElroy（1983）的速度色散被严重低估（高达50 km/s），以前的动力学模型低估了M31的膨胀的恒星质量的2倍。此外，星系的轻重量速度色散增长到166公里/秒，从而减少了M31中心黑洞的预测和测量质量之间的差异。运动位置角随距离变化，指向三轴性。我们探测到气体在膨胀短轴附近反向旋转。我们测量了八个排放校正的舔指数。它们在圆上近似恒定。我们得到的年龄，金属丰度和α元素丰度剖面。除了星系内部的弧秒区域外，M31的凸起都是一致的古老（>12 Gyr，在15 Gyr的模型网格极限下有许多最佳拟合年龄），α元素略微过剩（[α/Fe]~0.2），并且处于太阳金属丰度，这与对恒星成分的解析研究一致。预测的u-g，g-r和r-i斯隆颜色配置文件匹配相当不错的灰尘校正的意见。恒星星族具有近似恒定的径向质光比（Kroupa IMF的M/L_R ~ 4-4.5），这与基于我们新的速度色散的恒星动力学估计一致。在内弧秒内，光度加权年龄下降到4-8 Gyr，而金属丰度增加到太阳值的3倍以上。
英文摘要：
We present new optical long-slit data along 6 position angles of the bulge region of M31. We derive accurate stellar and gas kinematics reaching 5 arcmin from the center, where the disk light contribution is always less than 30%, and out to 8 arcmin along the major axis, where the disk makes 55% of the total light. We show that the velocity dispersions of McElroy (1983) are severely underestimated (by up to 50 km/s) and previous dynamical models have underestimated the stellar mass of M31's bulge by a factor 2. Moreover, the light-weighted velocity dispersion of the galaxy grows to 166 km/s, thus reducing the discrepancy between the predicted and measured mass of the black hole at the center of M31. The kinematic position angle varies with distance, pointing to triaxiality. We detect gas counterrotation near the bulge minor axis. We measure eight emission-corrected Lick indices. They are approximately constant on circles. We derive the age, metallicity and alpha-element overabundance profiles. Except for the region in the inner arcsecs of the galaxy, the bulge of M31 is uniformly old (>12 Gyr, with many best-fit ages at the model grid limit of 15 Gyr), slightly alpha-elements overabundant ([alpha/Fe]~0.2) and at solar metallicity, in agreement with studies of the resolved stellar components. The predicted u-g, g-r and r-i Sloan color profiles match reasonably well the dust-corrected observations. The stellar populations have approximately radially constant mass-to-light ratios (M/L_R ~ 4-4.5 for a Kroupa IMF), in agreement with stellar dynamical estimates based on our new velocity dispersions. In the inner arcsecs the luminosity-weighted age drops to 4-8 Gyr, while the metallicity increases to above 3 times the solar value.
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