论文标题
追踪M101的贫血恒星光环
Tracing the anemic stellar halo of M101
论文作者
论文摘要
在宇宙学环境中，星系形成的模型预测，巨大的磁盘星系应具有结构化的延伸恒星光环。然而，最近在综合光中的研究报告了一些星系，包括附近的磁盘Galaxy M101，这些星系没有可测量的恒星晕对检测极限。我们旨在通过解决恒星来量化M101郊区的出色内容和结构。我们根据鬼魂调查的一部分，根据深层F606W和使用哈勃太空望远镜拍摄的F814W图像介绍其恒星的光度法。恒星的构造CMD延伸到红色巨型分支尖端下方的两个幅度。我们得出了亮红色巨型分支（RGB）星的径向数密度谱。 $ r \ sim $ 40-60 kpc的RGB星的平均颜色与银河系中的金属贫困球状簇相似。我们还使用蜻蜓团队提供的公共图像数据得出了径向表面亮度曲线。径向数密度和表面亮度曲线均转化为径向质量密度曲线并组合。我们发现，质量密度曲线在非常外部的区域显示出较弱的上流，其中表面亮度像$μ_g\ \ 34 $ mag arcsec $^{ - 1} $一样微弱。质量密度概要文件上的指数磁盘 +幂律光晕模型找到了$ M_ {halo} = 8.2 _ { - 2.2}^{ + 3.5} \ times 10^7m_ \ odot $的总恒星光环质量。当考虑强截断磁盘模型时，总恒星光环质量不超过$ m_ {halo} = 3.2 \ times 10^8 $ $ m _ {\ odot} $。将光晕质量与M101的总恒星质量相结合，我们获得了$ M_ {halo}/m_ {gal} = 0.20 _ { - 0.08}^{+0.10} \％$，上限为0.78 \％。我们将M101的光环特性与六个幽灵调查星系以及银河系和M31的光环特性进行了比较，并发现M101具有贫血的恒星光环。
Models of galaxy formation in a cosmological context predict that massive disk galaxies should have structured extended stellar halos. Recent studies in integrated light, however, report a few galaxies, including the nearby disk galaxy M101, that have no measurable stellar halos to the detection limit. We aim to quantify the stellar content and structure of M101's outskirts by resolving its stars. We present the photometry of its stars based on deep F606W and F814W images taken with Hubble Space Telescope as part of the GHOSTS survey. The constructed CMDs of stars reach down to two magnitudes below the tip of the red giant branch. We derived radial number density profiles of the bright red giant branch (RGB) stars. The mean color of the RGB stars at $R \sim$ 40 -- 60 kpc is similar to those of metal-poor globular clusters in the Milky Way. We also derived radial surface brightness profiles using the public image data provided by the Dragonfly team. Both the radial number density and surface brightness profiles were converted to radial mass density profiles and combined. We find that the mass density profiles show a weak upturn at the very outer region, where surface brightness is as faint as $μ_g\approx 34$ mag arcsec$^{-1}$. An exponential disk + power-law halo model on the mass density profiles finds the total stellar halo mass of $M_{halo}=8.2_{-2.2}^{+3.5}\times 10^7M_\odot$. The total stellar halo mass does not exceed $M_{halo} = 3.2 \times 10^8$ $M_{\odot}$ when strongly truncated disk models are considered. Combining the halo mass with the total stellar mass of M101, we obtain the stellar halo mass fraction of $M_{halo}/M_{gal} = 0.20_{-0.08}^{+0.10}\%$ with an upper limit of 0.78\%. We compare the halo properties of M101 with those of six GHOSTS survey galaxies as well as the Milky Way and M31 and find that M101 has an anemic stellar halo.
