GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. II. METALLICITY PROFILE
GLOBAL PROPERTIES OF M31'S STELLAR HALO FROM THE SPLASH SURVEY. II. METALLICITY PROFILE
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DOI：
10.1088/0004-637x/796/2/76
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发表时间：
2014-09
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通讯作者：
K. Gilbert;J. Kalirai;P. Guhathakurta;R. Beaton;M. Geha;E. Kirby;S. Majewski;R. Patterson;E. Tollerud;J. Bullock;Mikito Tanaka;M. Chiba
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作者：
K. Gilbert;J. Kalirai;P. Guhathakurta;R. Beaton;M. Geha;E. Kirby;S. Majewski;R. Patterson;E. Tollerud;J. Bullock;Mikito Tanaka;M. Chiba
我们提出的金属丰度分布的红巨星分支（RGB）恒星在M31的恒星晕，来自光度金属丰度估计超过1500光谱确认的RGB晕星。恒星样本来自凯克/DEIMOS摄谱仪观测到的38个晕场，距离M31中心的投影距离从9到175千秒差距不等，其中包括52颗已确认的超过100千秒差距的M31晕星。虽然在整个晕中可以看到各种各样的金属丰度，但随着半径的增加，金属丰度分布函数的富金属峰变得不那么突出。M31恒星晕的金属丰度剖面显示出从9到100 kpc的连续梯度，星等为-0.01 dex kpc-1。在每个领域的恒星速度分布被用来识别恒星可能与潮汐碎片功能。潮汐碎片特征的去除并没有显著改变M31晕中的金属丰度梯度：在跨度为10-90千秒差距的区域中保持着一个梯度。我们分析的晕金属丰度配置文件，以及与潮汐碎片功能和底层晕人口的恒星的相对金属丰度，在当前模拟恒星晕形成的背景下。我们认为，M31晕中的大规模梯度意味着M31过去至少吸积了一个相对巨大的祖先，而金属丰度剖面中观察到的场与场的变化表明多个较小的祖先可能对M31的外晕做出了重大贡献。
We present the metallicity distribution of red giant branch (RGB) stars in M31's stellar halo, derived from photometric metallicity estimates for over 1500 spectroscopically confirmed RGB halo stars. The stellar sample comes from 38 halo fields observed with the Keck/DEIMOS spectrograph, ranging from 9 to 175 kpc in projected distance from M31's center, and includes 52 confirmed M31 halo stars beyond 100 kpc. While a wide range of metallicities is seen throughout the halo, the metal-rich peak of the metallicity distribution function becomes significantly less prominent with increasing radius. The metallicity profile of M31's stellar halo shows a continuous gradient from 9 to ∼100 kpc, with a magnitude of ∼ − 0.01 dex kpc−1. The stellar velocity distributions in each field are used to identify stars that are likely associated with tidal debris features. The removal of tidal debris features does not significantly alter the metallicity gradient in M31's halo: a gradient is maintained in fields spanning 10–90 kpc. We analyze the halo metallicity profile, as well as the relative metallicities of stars associated with tidal debris features and the underlying halo population, in the context of current simulations of stellar halo formation. We argue that the large-scale gradient in M31's halo implies M31 accreted at least one relatively massive progenitor in the past, while the field to field variation seen in the metallicity profile indicates that multiple smaller progenitors are likely to have contributed substantially to M31's outer halo.