文章基本信息

标题：Project AMIGA: Distance and Metallicity Gradients along Andromeda’s Giant Southern Stream from the Red Clump
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作者：Roger E. Cohen ; Jason S. Kalirai ; Karoline M. Gilbert 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2018
卷号：156
期号：5
页码：1-23
DOI：10.3847/1538-3881/aae52d
语种：English
出版社：American Institute of Physics
摘要：The Giant Southern Stream (GSS) of M31, a keystone signature of a major accretion event, yields crucial constraints on M31 formation and evolution models. Currently, our understanding of the GSS, in terms of both its geometry and its chemistry, results from either wide-field imaging probing only a few magnitudes below the red giant branch tip, or deep imaging or spectroscopy of isolated regions. Here, we take an alternative approach, using Hubble Space Telescope (HST) imaging to characterize the horizontal branch red clump (RC) using unbinned maximum likelihood fits to luminosity functions from observed color–magnitude diagrams. Comparing the RC mean magnitude across three fields at projected distances of 21, 52, and 80kpc from M31, we find a line-of-sight distance gradient identical to recent literature measurements in fields along the core. We also find tentative evidence that the line-of-sight distance dispersion increases with projected distance from M31. Meanwhile, the metallicity in the 52 kpc field westward of the GSS core is at least as high as that in the 21 kpc GSS core field, and the peak colors of the RC in these two fields imply identical metallicities to within 0.2 dex. We discuss implications for distance and metallicity gradients both along and perpendicular to the GSS in the context of recent ground-based photometric and spectroscopic results, including evidence for a dropoff in metallicity moving westward from the GSS, as well as prospects for further constraining stellar populations in the vicinity of the GSS.
关键词：galaxies: evolution;galaxies: individual (M31);galaxies: stellar content;galaxies: structure;stars: horizontal-branch