发表机构
Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
该研究通过半解析化学演化模型结合贝叶斯框架，探究热模式吸积与角动量守恒对星系盘金属丰度梯度的影响，拟合银河系数据并为约束外部星系热吸积提供新方法。
AI 中文摘要
星系的热星系际介质（CGM）由于对引力的压力支撑更高，其旋转速度必然慢于它所包围的星系盘中的冷气体。若热CGM垂直吸积到星系盘，角动量守恒会引发径向流动，将金属向内平流并使金属丰度梯度变陡。因此观测到的梯度携带了吸积气体运动学的信息。以往基于这一前提的模型，将角动量不匹配参数化为随时间恒定的简单半径函数，而非从CGM自身性质推导。本文提出了一个星系的半解析化学演化模型，该模型具有受宇宙学启发的演化过程、自洽且随时间演化的引力势，以及等温旋转的CGM。模型包含由引力势阱加深（作用于气体和恒星）以及吸积所引发的径向流动，研究这些因素对气体相金属丰度梯度在宇宙时间内的综合影响。我们采用贝叶斯框架同时拟合星系的结构性质和金属丰度梯度，推断所需的内外生长模式以及驱动径向流动和丰度梯度所需的CGM温度。将模型应用于银河系拟合后，我们发现对亚维里冕（$T_\text{CGM}/T_{200}=0.82^{+0.44}_{-0.38}$）存在微弱偏好，这与观测结果存在轻微张力，并讨论了可能的解决方案。当前预测的CGM旋转速度约为100-160 km/s，在更早的时代则显著更低。我们还恢复了过去约8 Gyr内梯度的演化，与观测结果一致。我们的方法不限于银河系，可直接应用于外部星系，为约束星系盘的热模式吸积提供了新的手段。
英文摘要
The hot circumgalactic medium (CGM) of a galaxy inevitably rotates more slowly than the cold gas in the disc it surrounds, due to a higher pressure support against gravity. If it accretes vertically onto the disc, angular momentum conservation leads to radial flows, advection of metals inwards and the steepening of a metallicity gradient. The observed gradient hence carries information on the kinematics of the accreting gas. Previous models built on this premise parametrised the angular momentum mismatch as a simple function of radius, constant in time, rather than derived from the properties of the CGM itself. Here, we present a semi-analytic chemical evolution model of a galaxy with a cosmologically motivated evolution, a self-consistent and time-evolving potential and an isothermal rotating CGM. The model includes inside-out formation and the radial flows induced both by the deepening of the potential well (acting on gas and stars) and by accretion, following their combined effect on the gas-phase metallicity gradient over cosmic time. We use a Bayesian framework to fit simultaneously the structural properties and metallicity gradient of a galaxy, inferring both the required inside-out growth and the CGM temperature needed to drive the required radial flows and abundance gradient. Fitting our model to the Milky Way, we find a mild preference for a subvirial corona ($T_\mathrm{CGM}/T_{200}=0.82^{+0.44}_{-0.38}$), in mild tension with observations, and we discuss possible resolutions. The predicted CGM rotation velocity lies between ~100-160 km/s at the present time and is substantially lower at earlier epochs. We further recover an evolution of the gradient over the past ~8Gyr consistent with observations. Our approach is not restricted to the Milky Way and can be directly applied to external galaxies, offering a new handle to constrain hot mode accretion onto galactic discs.
Comments27 pages, 20 figures. Submitted to A&A
