测试从最小观测数据估计星系质量的简单方法
Testing a simple recipe for estimating galaxy masses from minimal observational data
摘要：
一个简单的方法来估计一个星系的总质量分布的准确性和鲁棒性进行了测试，使用样本的65个宇宙学变焦模拟的单个星系。该方法只需要光学表面亮度和投影速度色散廓线的信息，因此即使在观测数据较差的情况下也可以应用。在模拟的样本星系（$σ\simeq 200-400$ $\kms$）中，在很宽的半径范围内，$z=0$具有几乎等温的自转曲线（在$0.5R_{\rm eff} < r < 3R_{\rm eff}$上圆速度偏离一个常数的RMS $\simeq 5%$）。对于这样的星系的方法恢复无偏值的圆速度。在$\simeq 5-8%$（RMS）的离散度高达$R \simeq 5R_{\rm eff}$的情况下，样品平均与真实圆周速度的偏差小于$\sim 1%$。在较高的红移（$z=1$和$z=2$）的大质量非旋转模拟星系的圆周速度估计也几乎是无偏的，具有相同的散射。对于样本中质量最小的星系（$σ< 150$ $\kms$），在$z=0$的RMS偏差为$\simeq 7-9%$，平均偏差偏低约$1-2%$。我们还从流体静力平衡（HE）方程中得到了模拟星系中热气体的圆速度分布。这个估计的准确性大约是RMS $\simeq 4-5%$的大质量物体（$M > 6.5\times 10^{12} M_\odot$）和他的估计偏置低的$\simeq 3-4%$，这可以追溯到气体运动的存在。这意味着，简单的质量估计可以用来确定观测到的大质量椭圆星系的质量$5-8 %$的精度，可以是非常有用的星系调查。
英文摘要：
The accuracy and robustness of a simple method to estimate the total mass profile of a galaxy is tested using a sample of 65 cosmological zoom-simulations of individual galaxies. The method only requires information on the optical surface brightness and the projected velocity dispersion profiles and therefore can be applied even in case of poor observational data. In the simulated sample massive galaxies ($σ\simeq 200-400$ $\kms$) at redshift $z=0$ have almost isothermal rotation curves for broad range of radii (RMS $\simeq 5%$ for the circular speed deviations from a constant value over $0.5R_{\rm eff} < r < 3R_{\rm eff}$). For such galaxies the method recovers the unbiased value of the circular speed. The sample averaged deviation from the true circular speed is less than $\sim 1%$ with the scatter of $\simeq 5-8%$ (RMS) up to $R \simeq 5R_{\rm eff}$. Circular speed estimates of massive non-rotating simulated galaxies at higher redshifts ($z=1$ and $z=2$) are also almost unbiased and with the same scatter. For the least massive galaxies in the sample ($σ< 150$ $\kms$) at $z=0$ the RMS deviation is $\simeq 7-9%$ and the mean deviation is biased low by about $1-2%$. We also derive the circular velocity profile from the hydrostatic equilibrium (HE) equation for hot gas in the simulated galaxies. The accuracy of this estimate is about RMS $\simeq 4-5%$ for massive objects ($M > 6.5\times 10^{12} M_\odot$) and the HE estimate is biased low by $\simeq 3-4%$, which can be traced to the presence of gas motions. This implies that the simple mass estimate can be used to determine the mass of observed massive elliptical galaxies to an accuracy of $5-8 %$ and can be very useful for galaxy surveys.
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