NGC 6822的AGB群体：分布和来自JHK光度测定的C/M比值
The AGB population of NGC 6822: distribution and the C/M ratio from JHK photometry
摘要：
NGC 6822是一个不规则矮星系，属于本星系群。它的近距离和明显的孤立提供了一个独特的机会，研究星系演化没有任何明显的强烈的外部影响。本文研究了NGC 6822中渐近巨星支（AGB）粒子数和金属丰度的空间分布。使用深，高质量的JHK测光，采取与WFCAM的UKIRT，富碳和富氧的AGB星已被隔离。它们的数量之比，C/M比，然后被用来推导整个星系的[Fe/H]丰度。红巨星分支的尖端位于K 0 = 17.41 \pm 0.11等，富碳和富氧AGB星的颜色分离在（J-K）0 = 1.20 \pm 0.03等（即（J-K）2 MAS S » 1.28等）。在星系内部4 kpc的C/M比为0.62 \pm 0.03，这意味着铁的丰度为[Fe/H] = -1.29 \pm 0.07 dex。这些参数的变化进行了研究，作为一个函数的距离星系中心和方位角。NGC 6822的AGB星群被探测到半径为4kpc，直径为56弧分。它是贫金属的，但没有明显的梯度，无论是从中心的径向距离或方位角的金属。在TRGB星等的检测传播是一致的，一个星系所包围的光环的老恒星。的C/M比有可能是一个非常有用的工具，用于确定金属丰度在解决星系，但更好地校准的C/M与[Fe/H]的关系和更好地理解的敏感性的C/M比恒星选择标准是首先需要的。
英文摘要：
NGC 6822 is an irregular dwarf galaxy and part of the Local Group. Its close proximity and apparent isolation provide a unique opportunity to study galactic evolution without any obvious strong external influences. This paper aims to study the spatial distribution of the asymptotic giant branch (AGB) population and metallicity in NGC 6822. Using deep, high quality JHK photometry, taken with WFCAM on UKIRT, carbon- and oxygen-rich AGB stars have been isolated. The ratio between their number, the C/M ratio, has then been used to derive the [Fe/H] abundance across the galaxy. The tip of the red giant branch is located at K0 = 17.41 \pm 0.11 mag and the colour separation between carbon- and oxygen-rich AGB stars is at (J - K)0 = 1.20 \pm 0.03 mag (i.e. (J - K)2MAS S » 1.28 mag). A C/M ratio of 0.62 \pm 0.03 has been derived in the inner 4 kpc of the galaxy, which translates into an iron abundance of [Fe/H] = -1.29\pm0.07 dex. Variations of these parameters were investigated as a function of distance from the galaxy centre and azimuthal angle. The AGB population of NGC 6822 has been detected out to a radius of 4 kpc giving a diameter of 56 arcmin. It is metal-poor, but there is no obvious gradient in metallicity with either radial distance from the centre or azimuthal angle. The detected spread in the TRGB magnitude is consistent with that of a galaxy surrounded by a halo of old stars. The C/M ratio has the potential to be a very useful tool for the determination of metallicity in resolved galaxies but a better calibration of the C/M vs. [Fe/H] relation and a better understanding of the sensitivities of the C/M ratio to stellar selection criteria is first required.
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