Title: The Low-Redshift Lyman Continuum Survey: Optically Thin and Thick Mg II Lines as Probes of Lyman Continuum Escape Show Chinese title

Title: 低红移Lyman连续谱调查：光学薄和厚Mg II线作为Lyman连续谱逃逸的探针

Abstract: The Mg II 2796, 2803 doublet has been suggested to be a useful indirect indicator for the escape of Ly-alpha and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg II or strong LyC emission. Here we present the first study of Mg II probing a large dynamic range of galaxy properties, using newly obtained high signal-to-noise, moderate-resolution spectra of Mg II for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg II profiles ranging from strong emission to P-Cygni profiles, and to pure absorption. We find there is a significant trend (with a possibility of spurious correlations of ~ 2%) that galaxies detected as strong LyC Emitters (LCEs) also show larger equivalent widths of Mg II emission, and non-LCEs tend to show evidence of more scattering and absorption features in Mg II We then find Mg II strongly correlates with Ly-alpha in both equivalent width and escape fraction, regardless of whether the emission or absorption dominates the Mg II profiles. Furthermore, we present that, for galaxies categorized as Mg II emitters (MgE), one can adopt the information of Mg II, metallicity, and dust to estimate the escape fraction of LyC within a factor of 3. These findings confirm that Mg II lines can be used as a tool to select galaxies as LCEs and to serve as an indirect indicator for the escape of Ly-alpha and LyC. Show Chinese abstract

Abstract: 镁II 2796, 2803双线被认为是一个有用的间接指标，用于指示本地形成星系中Ly-alpha和Lyman连续谱（LyC）光子的逃逸。 然而，迄今为止的研究主要集中在具有强镁II或强LyC发射的小样本星系上。 在这里，我们展示了首次利用新获得的高信噪比、中等分辨率的镁II光谱对34个星系进行的大动态范围星系特性研究，这些星系选自低红移Lyman连续谱调查。 我们显示，我们的样本中的星系具有从强发射到P-Cygni轮廓再到纯吸收的镁II轮廓。 我们发现存在一个显著的趋势（可能存在约2%的虚假相关性），被检测为强LyC发射器（LCEs）的星系也表现出更大的镁II发射等值宽度，而非LCEs倾向于表现出更多的散射和吸收特征在镁II中。然后我们发现，无论发射或吸收主导镁II轮廓，镁II与Ly-alpha在等值宽度和逃逸率方面有很强的相关性。 此外，我们指出，对于被归类为镁II发射器（MgE）的星系，可以利用镁II的信息、金属丰度和尘埃来估算LyC的逃逸率，误差因子在3以内。 这些发现证实了镁II线可以作为选择LCEs星系的工具，并作为Ly-alpha和LyC逃逸的间接指标。