论文标题
指数恒星磁盘的起源
The Origin of Exponential Star-forming Disks
论文作者
论文摘要
星系的磁盘成分通常显示出指数曲线的范围，该曲线在质量和恒星形成率的几个比例长度上延伸，但物理起源尚不清楚。我们探索了一个物理模型，其中银河气磁盘被视为“修饰的积聚盘”，在该磁盘中，由磁盘中的粘应力驱动的共面气体流入为恒星形成提供了燃料，该燃料会逐渐消除，从而逐渐消除气体。我们表明，来自磁性旋转不稳定性的磁应力是所需粘度的最合理的来源，并构建了一个简单的物理模型来探索这一点。一个关键特征是将磁场强度与局部恒星形成表面密度联系起来，$ b _ {\ rm tot} \ proptoσ_{\ rm sfr}^α$。这提供了恒星形成和气体流之间的回馈环。我们发现该模型自然会产生稳定的稳态指数磁盘，长达$α\ sim $ 0.15，该值来自附近星系的空间分辨观测值。磁盘比例长度$ h _ {\ rm rm r} $是由磁盘的汇总设置的，通过$ b _ {\ rm tot} -t _ {\ rm sfr} $关系的归一化和晕圈的圆速度。气体和恒星在磁盘内的角动量分布是嵌入磁盘运行固有的角动量的结果，而不是流入材料的初始角动量。我们建议磁应力可能在建立银河系磁盘的稳定指数形式中起主要作用。
The disk components of galaxies generally show an exponential profile extending over several scale lengths, both in mass and star-formation rate, but the physical origin is not well understood. We explore a physical model in which the galactic gas disk is viewed as a "modified accretion disk" in which coplanar gas inflow, driven by viscous stresses in the disk, provides the fuel for star formation, which progressively removes gas as it flows inwards. We show that magnetic stresses from magneto-rotational instability are the most plausible source of the required viscosity, and construct a simple physical model to explore this. A key feature is to link the magnetic field strength to the local star-formation surface density, $B_{\rm tot} \propto Σ_{\rm SFR}^α$. This provides a feed-back loop between star-formation and the flow of gas. We find that the model naturally produces stable steady-state exponential disks, as long as $α\sim$ 0.15, the value indicated from spatially-resolved observations of nearby galaxies. The disk scale-length $h_{\rm R}$ is set by the rate at which the disk is fed, by the normalization of the $B_{\rm tot}-Σ_{\rm SFR}$ relation and by the circular velocity of the halo. The angular momentum distribution of the gas and stars within the disk is a consequence of the transfer of angular momentum that is inherent to the operation of an accretion disk, rather than the initial angular momentum of the inflowing material. We suggest that magnetic stresses likely play a major role in establishing the stable exponential form of galactic disks.
