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arXiv 0811.1688astro-ph
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中心质量浓度对棒星系核螺旋形成的影响

Effect of Central Mass Concentration on the Formation of Nuclear Spirals in Barred Galaxies

Parijat Thakur, H. B. Ann, Ing-Guey Jiang

备注：
29 pages, 5 figures (Color Figures 3-5), Accepted for Publication in Astrophysical Journal (ApJ)
发表信息：
Astrophys.J.693:586-596,2009
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摘要：

我们进行了光滑粒子流体动力学（SPH）模拟研究的中心千秒差距区域的气体盘的非轴对称杆势的施加的响应。模型星系是由三个轴对称的组成部分（晕，盘，隆起）和一个非轴对称的酒吧。假设这些分量在与杆共转的框架中在时间上是不变的。球型$γ$ -Dehnen模型的势被用于其密度在中心附近为$r^{-γ}$而在较大半径处为$r^{-4}$的隆起分量，因此，具有$γ= 0$的中心密度核和$γ> 0$的尖点。由于模型星系的中心质量浓度随尖点参数$γ$的增大而增大，本文研究了尖点参数$γ$的变化对棒星系对称双臂核螺旋形成机制的影响。我们的模拟结果表明，对称的双臂核螺旋是由流体动力学的螺旋冲击驱动的杆的重力扭矩与$γ= 0$和0.5模型。另一方面，用气体密度波解释了具有$γ=1$和1.5的模型中的对称双臂核螺旋。因此，当中心质量浓度从$γ= 0$增加到1.5时，棒旋星系中对称双臂核涡旋的形成机制由流体动力学激波转变为气体密度波.

英文摘要：

We have performed smoothed particle hydrodynamics (SPH) simulations to study the response of the central kiloparsec region of a gaseous disk to the imposition of nonaxisymmetric bar potentials. The model galaxies are composed of the three axisymmetric components (halo, disk, and bulge) and a non-axisymmetric bar. These components are assumed to be invariant in time in the frame corotating with the bar. The potential of spherical $γ$-models of Dehnen is adopted for the bulge component whose density varies as $r^{-γ}$ near the center and $r^{-4}$ at larger radiiand hence, possesses a central density core for $γ= 0$ and cusps for $γ> 0$. Since the central mass concentration of the model galaxies increases with the cusp parameter $γ$, we have examined here the effect of the central mass concentration by varying the cusp parameter $γ$ on the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies. Our simulations show that the symmetric two-armed nuclear spirals are formed by hydrodynamic spiral shocks driven by the gravitational torque of the bar for the models with $γ= 0$ and 0.5. On the other hand, the symmetric two-armed nuclear spirals in the models with $γ=1$ and 1.5 are explained by gas density waves. Thus, we conclude that the mechanism responsible for the formation of the symmetric two-armed nuclear spirals in barred galaxies changes from the hydrodynamic shocks to the gas density waves when the central mass concentration increases from $γ= 0$ to 1.5.

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