恒星形成星系主序的客观定义
An Objective Definition for the Main Sequence of Star-Forming Galaxies
摘要：
恒星形成星系的主序星（Main Sequence，MS）在推动星系演化和理解星系演化中起着重要作用。然而，不同的研究发现MS的归一化、斜率和形状存在显著差异。这些差异主要是由于采用不同的选择标准来分离恒星形成星系，可能包括或排除比恒星形成率（SFR）远低于MS值的星系。为了克服目前所有标准的局限性，我们提出了一个客观的MS定义，它完全不依赖于恒星形成星系的预选。构建3D SFR-质量数图，然后将MS定义为恒星形成峰的脊线，如各种图所示。这种定义的好处是多方面的。如果普遍采用，它将有助于使用相同的恒星形成率（SFR）和恒星质量诊断的不同群体的结果进行相互比较，或突出不同诊断的相对系统性。所有这些都有助于将MS星系理解为处于准稳态平衡的系统，也将为识别淬火星系提供更客观的标准。
英文摘要：
The Main Sequence (MS) of star-forming galaxies plays a fundamental role in driving galaxy evolution and in our efforts to understand it. However, different studies find significant differences in the normalization, slope and shape of the MS. These discrepancies arise mainly from the different selection criteria adopted to isolate star-forming galaxies, that may include or exclude galaxies with specific star formation rate (SFR) substantially below the MS value. To obviate this limitation of all current criteria, we propose an objective definition of the MS that does not rely at all on a pre-selection of star-forming galaxies. Constructing the 3D SFR-Mass-Number plot, the MS is then defined as the ridge line of the star-forming peak, as illustrated with various figures. The advantages of such definition are manifold. If generally adopted it will facilitate the inter-comparison of results from different groups using the same star formation rate (SFR) and stellar mass diagnostics, or to highlight the relative systematics of different diagnostics. All this could help understanding MS galaxies as systems in a quasi-steady state equilibrium and would also provide a more objective criterion for identifying quenching galaxies.
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