Abstract

Integrated characteristics of a sample of 66 star-forming galaxies with extremely low oxygen abundances from the SDSS Data Release 14 are studied. The oxygen abundances were determined by the direct T_e method for 42 galaxies with detected [O III] 436.3 nm emission lines and by the strong-line method for the remaining galaxies. Derived abundances 12 + log (O/H) fall within the 6.97–7.52 range and are, on average, four times lower than the corresponding values for a large comparison sample of compact star-forming galaxies from the SDSS. Stellar masses and H_β luminosities for both samples were derived from SDSS spectra with a small spectroscopic aperture (2–3 arcsec in diameter). In order to determine their values for the entire galaxy, aperture corrections taking radiation outside the spectroscopic slit into account were introduced. Stellar masses and luminosities in the optical range are 100 times lower than the corresponding values for the galaxies from the comparison sample. At fixed values of luminosity and stellar mass, these galaxies have lower oxygen abundances in the oxygen abundance–luminosity and oxygen abundance–stellar mass diagrams than the galaxies from the main SDSS sample. This offset is likely caused by accretion of unenriched intergalactic gas, which reduces the oxygen abundance in the galactic interstellar medium. The majority of galaxies with extremely low oxygen abundances were detected in the mid-infrared range by the WISE space telescope. Color index W1 – W2, where W1 and W2 are the magnitudes at a wavelength of 3.4 and 4.6 μm, of these galaxies corresponds to the values typical for stellar emission and/or free-free ionized gas emission. The low ultraviolet luminosity, which is the main source of dust heating in star-forming galaxies, thus eliminates the possibility that warm and hot dust is present.

中文翻译：

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极低氧丰度的SDSS DR14星型星系的综合特性

摘要

研究了来自SDSS数据发布14的66个具有极低氧丰度的恒星形成星系样本的综合特性。氧丰度是通过直接T _e方法对检测到[O III] 436.3 nm发射线的星系进行测定的，而对于其余星系则采用强线测定法进行的。衍生丰度12 + log（O / H）落在6.97-7.52范围内，平均比SDSS的大型紧凑恒星形成星系比较样本的相应值低四倍。恒星质量和_Hβ两种样品的光度均来自具有较小光谱孔径（直径2-3 arcsec）的SDSS光谱。为了确定它们在整个银河系中的值，引入了将光谱狭缝外部的辐射考虑在内的孔径校正。光学范围内的恒星质量和亮度比比较样品中星系的相应值低100倍。在固定的亮度和恒星质量值下，这些星系在氧丰度（发光度和氧丰度）星状质量图中的氧丰度比主要SDSS样本的星系低。这种偏移可能是由于未富集星系间气体的积聚引起的，这会减少星系星际介质中的氧丰度。WISE太空望远镜在中红外范围内发现了大多数氧含量极低的星系。颜色指数W 1 – W 2，其中W 1和W 2是在3.4和4.6μm波长处的大小，这些星系对应于恒星发射和/或自由离子电离气体发射的典型值。低紫外线发光度是形成恒星的星系中尘埃加热的主要来源，因此消除了存在热尘和热尘的可能性。