z ~ 0.3–0.4 LyC 泄漏星系中 CNO 元素的丰度
Abundances of CNO elements in z ~ 0.3-0.4 LyC leaking galaxies
AI总结：
研究结合HST/STIS与SDSS光谱测定z~0.3–0.4 LyC泄漏星系及文献星系的C、N、O丰度，揭示C/O随金属丰度和恒星质量的变化及N/O增强趋势。
摘要：
我们展示了哈勃空间望远镜（Hubble Space Telescope）上空间望远镜成像光谱仪（Space Telescope Imaging Spectrograph，STIS）对11个红移 z 位于0.29–0.43范围内的莱曼连续谱（Lyman continuum，LyC）泄漏星系的观测，其氧丰度为12+log(O/H)=7.64–8.16，恒星质量 Mstar~10^7.8–10^9.8 Msun，O32=[OIII]5007/[OII]3727约为5–20，观测旨在探测CIII]1908发射线。我们将这些观测与光学的斯隆数字巡天（Sloan Digital Sky Survey，SDSS）光谱相结合，以测定碳、氮和氧的丰度。我们的样本由文献中的31个星系补充，对于这些星系，可以从HST和SDSS光谱中导出碳、氮和氧丰度。然而，这些额外星系没有LyC观测。我们发现，在12+log(O/H)<8.1时，整个样本的log(C/O)不依赖于金属丰度，在约-0.75 dex的平均值附近具有约0.13 dex的小弥散。另一方面，与样本中其余金属丰度较低的星系相比，z>0.1的星系（包括LyC泄漏星系）中的log(N/O)系统性更高。我们发现log(C/O)随着Mstar增加而略微降低，从Mstar=10^6 Msun时的约-0.65降至Mstar=10^9–10^10 Msun时的约-0.80，而log(N/O)在Mstar>10^8 Msun时显著增强。这些趋势的起源基本上仍不清楚。一种可能的解释是假设质量更大的星系中恒星初始质量函数（initial mass function，IMF）的质量上限更高。这将导致更高的氧产量，以及更大比例的大质量恒星通过星风用氮污染星际介质。
英文摘要：
We present observations with the Space Telescope Imaging Spectrograph (STIS) onboard the Hubble Space Telescope of eleven Lyman continuum (LyC) leaking galaxies at redshifts, z, in the range 0.29-0.43, with oxygen abundances 12+log(O/H)=7.64-8.16, stellar masses Mstar~10^7.8-10^9.8 Msun and O32=[OIII]5007/[OII]3727 of ~5-20, aiming to detect CIII]1908 emission line. We combine these observations with the optical Sloan Digital Sky Survey (SDSS) spectra for the determination of carbon, nitrogen and oxygen abundances. Our sample was supplemented by thirty one galaxies from the literature, for which carbon, nitrogen and oxygen abundances can be derived from the HST and SDSS spectra. These additional galaxies, however, do not have LyC observations. We find that log(C/O) for the entire sample at 12+log(O/H)<8.1 does not depend on metallicity, with a small dispersion of ~0.13 dex around the average value of ~ -0.75 dex. On the other hand, the log(N/O) in galaxies at z>0.1, including LyC leakers, is systematically higher compared to the rest of the sample with lower metallicity. We find that log(C/O) slightly decreases with increasing Mstar from ~ -0.65 at Mstar=10^6 Msun to ~ -0.80 at Mstar=10^9-10^10 Msun, whereas log(N/O) is considerably enhanced at Mstar>10^8 Msun. The origin of these trends remains basically unknown. One of the possible solutions is to assume that the upper mass limit of the stellar initial mass function (IMF) in more massive galaxies is higher. This would result in higher production of oxygen and larger fraction of massive stars with stellar wind polluting interstellar medium with nitrogen.
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