芝加哥哈勃计划V.通过红巨星分支的尖端到NGC 1448和NGC 1316的距离
The Carnegie-Chicago Hubble Program. V. The Distances to NGC 1448 and NGC 1316 via the Tip of the Red Giant Branch
摘要：
芝加哥-芝加哥哈勃计划（CCHP）正在重新校准银河系外超新星Ia的距离尺度，只使用星族II恒星。这项工作的重点是红巨星分支（TRGB）的方法，其系统学是完全独立的人口I造父变星为基础的测定，长期以来一直作为校准的SN Ia距离尺度。我们提出了深哈勃太空望远镜成像的低表面密度和低视线变红晕的两个星系，NGC 1448和NGC 1316，其中每一个都是主机最近的超新星Ia事件。暂时将TRGB零点锚定在从分离的食双星得到的到大麦云云的几何距离上，我们测量到NGC 1448和NGC 1316的反射修正距离模量分别为31.23 +/-0.04（stat）+/-0.06（sys）等，给出17.7 +/- 0.3（stat）+/- 0.5（sys）Mpc和18.8 +/- 0.3（stat）+/- 0.5（sys）Mpc的度量距离。我们发现我们的结果与NGC 1448的造父变星距离之间的一致性;对于NGC 1316，基于直接测量的距离相对较少，我们发现我们的结果与已公布的SN Ia距离一致，其绝对尺度是从其他本地确定的方法，如造父变星。对于NGC 1448和NGC 1316，我们的距离是最精确（和系统准确）的测量，误差分别为1.7（2.8）%和1.6（2.7）%。
英文摘要：
The Carnegie-Chicago Hubble Program (CCHP) is re-calibrating the extragalactic SN Ia distance scale using exclusively Population II stars. This effort focuses on the Tip of the Red Giant Branch (TRGB) method, whose systematics are entirely independent of the Population I Cepheid-based determinations that have long served as calibrators for the SN Ia distance scale. We present deep Hubble Space Telescope imaging of the low surface-density and low line-of-sight reddening halos of two galaxies, NGC 1448 and NGC 1316, each of which have been hosts to recent SN Ia events. Provisionally anchoring the TRGB zero-point to the geometric distance to the Large Magellanic Cloud derived from detached eclipsing binaries, we measure extinction-corrected distance moduli of 31.23 +/-0.04 (stat) +/- 0.06 (sys) mag for NGC 1448 and 31.37 +/- 0.04 (stat) and +/- 0.06 (sys) mag for NGC 1316, respectively, giving metric distances of 17.7 +/- 0.3 (stat) +/- 0.5 (sys) Mpc, and 18.8 +/- 0.3 (stat) +/- 0.5 (sys) Mpc. We find agreement between our result and the available Cepheid distance for NGC 1448; for NGC 1316, where there are relatively few published distances based on direct measurements, we find that our result is consistent with the published SN Ia distances whose absolute scales are set from other locally-determined methods such as Cepheids. For NGC 1448 and NGC 1316, our distances are some of the most precise (and systematically accurate) measurements with errors at 1.7 (2.8) % and 1.6 (2.7) % levels, respectively.
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