金属丰度梯度测量中的系统学I：角分辨率、信噪比和环隙分级
Systematics in Metallicity Gradient Measurements I : Angular Resolution, Signal-to-Noise and Annuli Binning
摘要：
随着高红移金属丰度梯度研究的快速发展，深入理解高红移金属丰度梯度测量的系统学意义显得尤为重要。这项工作研究了如何[NII]/H α比值的金属丰度梯度的变化与角分辨率，信号噪声（S/N），和环形分箱参数。使用两种方法：1。我们降低了引力透镜星系的高角分辨率积分场数据，并重新推导了不同角分辨率下的金属丰度梯度。利用一个已知梯度的局域星系，模拟了不同角分辨率和信噪比条件下的高红移积分场光谱（IFS）观测。我们发现，测量的金属丰度梯度的变化系统的角分辨率和环形分仓。与较高角分辨率的观测相比，可见度有限的观测产生明显更平坦的梯度。存在一个临界角分辨率极限，超过该极限，测量的金属丰度梯度与本征梯度显著不同。这个临界角分辨率取决于星系的内在梯度，对于我们模拟的星系来说，它小于0.02角秒。我们发现，看到有限的高红移金属丰度梯度很可能受到强烈的影响，分辨率驱动的梯度平坦化。由于弱的线拖尾，具有少量环的环形分箱产生比固有梯度更平坦的梯度。对于3-annuli bin，[NII]线上的最小S/N为~5是最微弱的环所需的，以限制具有有意义误差的梯度。
英文摘要：
With the rapid progress in metallicity gradient studies at high-redshift, it is imperative that we thoroughly understand the systematics in these measurements. This work investigates how the [NII]/Halpha ratio based metallicity gradients change with angular resolution, signal-to-noise (S/N), and annular binning parameters. Two approaches are used: 1. We downgrade the high angular resolution integral-field data of a gravitationally lensed galaxy and re-derive the metallicity gradients at different angular resolution; 2. We simulate high-redshift integral field spectroscopy (IFS) observations under different angular resolution and S/N conditions using a local galaxy with a known gradient. We find that the measured metallicity gradient changes systematically with angular resolution and annular binning. Seeing-limited observations produce significantly flatter gradients than higher angular resolution observations. There is a critical angular resolution limit beyond which the measured metallicity gradient is substantially different to the intrinsic gradient. This critical angular resolution depends on the intrinsic gradient of the galaxy and is < 0.02 arcsec for our simulated galaxy. We show that seeing-limited high-redshift metallicity gradients are likely to be strongly affected by resolution-driven gradient flattening. Annular binning with a small number of annuli produces a more flattened gradient than the intrinsic gradient due to weak line smearing. For 3-annuli bins, a minimum S/N of ~ 5 on the [NII] line is required for the faintest annulus to constrain the gradients with meaningful errors.
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