MaNGA中的非对称漂移：星系盘内质量与半径相关的分层速率
Asymmetric drift in MaNGA: Mass and radially-dependent stratification rates in galaxy disks
AI总结：
本文利用MaNGA巡天约500个邻近盘星系测量非对称漂移，发现恒星速度弥散随年龄的幂律分层参数b_r随星系质量增大、随半径减小，且MaNGA星系的非对称漂移幅度大于银河系，表明典型盘星系可能比银河系动力学上更热。
摘要：
我们利用SDSS-IV中MaNGA巡天观测的约500个邻近盘星系，通过电离气体与恒星切向速度之间的滞后测量了年龄-速度关系。所选星系在运动学上是轴对称的。速度滞后即非对称漂移，在银河系太阳邻域及其他本星系群星系中均有观测到；其幅度与恒星族年龄相关。该趋势在速率（d(sigma)/dt）上与一个简单的幂律模型定性一致，该模型中sigma正比于t^b，能够解释太阳邻域内的动力学相空间分层。该模型基于盘动力学时标被推广到其他半径和其他星系。我们发现MaNGA星系的面内径向分层参数sigma_(0,r}（最年轻星族的弥散度）在10-40 km/s范围内，且0.2<b_r<0.5。总体而言，b_r随星系质量增大而增大；对于恒星质量高于10.4 dex（太阳质量）的星系，b_r随半径增大而减小，但在较低质量星系中b_r随半径大致保持不变。测量弥散表明该分层模型过于简单，无法捕捉数据中呈现的复杂性，考虑到可能导致恒星族动力学分层的众多天体物理过程，这并不令人意外。尽管如此，数据表明动力学分层在星系群体中广泛存在，并在质量和密度上呈现系统性趋势。MaNGA样本的非对称漂移信号幅度比银河系更大，在平均值上更接近M31和M33盘中所观测到的情形。要么典型盘具有更高的面密度，要么更可能的是它们在动力学上比银河系更热（因而更厚）。
英文摘要：
We measure the age-velocity relationship from the lag between ionized gas and stellar tangential speeds in ~500 nearby disk galaxies from MaNGA in SDSS-IV. Selected galaxies are kinematically axisymmetric. Velocity lags are asymmetric drift, seen in the Milky Way's (MW) solar neighborhood and other Local Group galaxies; their amplitude correlates with stellar population age. The trend is qualitatively consistent in rate (d(sigma)/dt) with a simple power-law model where sigma is proportional to t^b that explains the dynamical phase-space stratification in the solar neighborhood. The model is generalized based on disk dynamical times to other radii and other galaxies. We find in-plane radial stratification parameters sigma_(0,r} (dispersion of the youngest populations) in the range of 10-40 km/s and 0.2<b_r<0.5 for MaNGA galaxies. Overall b_r increases with galaxy mass, decreases with radius for galaxies above 10.4 dex (M_solar) in stellar mass, but is ~constant with radius at lower mass. The measurement scatter indicates the stratification model is too simple to capture the complexity seen in the data, unsurprising given the many possible astrophysical processes that may lead to stellar population dynamical stratification. Nonetheless, the data show dynamical stratification is broadly present in the galaxy population, with systematic trends in mass and density. The amplitude of the asymmetric drift signal is larger for the MaNGA sample than the MW, and better represented in the mean by what is observed in the disks of M31 and M33. Either typical disks have higher surface-density or, more likely, are dynamically hotter (hence thicker) than the MW.
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