arXiv 1304.42392013-04-15astro-ph.COastro-ph.GA

低质量星系的金属丰度演化：中等红移的新限制

The metallicity evolution of low mass galaxies: New constraints at intermediate redshift

Alaina Henry, Crystal L. Martin, Kristian Finlator, Alan Dressler

备注：: Accepted for publication in ApJ
DOI：: 10.1088/0004-637X/769/2/148

摘要：

我们目前的丰度测量从26个发射线选定的星系在z~0.6-0.7。通过达到低至10^8 M_{\sun}的恒星质量，这些观测提供了低于10^9 M_{\sun}的中间红移质量-金属丰度（MZ）关系的第一次测量。对于我们的样本中M > 10^9 M_{\sun}的部分（8/26个星系），我们发现与先前测量的中间红移MZ关系非常一致。本地关系相比，我们测量的演变，对应于0.12德克斯减少在中间红移的氧丰度。这一结果证实了金属丰度演化的趋势变得更加显着，对较低的恒星质量，在缩小规模的情况下，低质量星系演变到当地的MZ关系在以后的宇宙时间。我们发现，这些星系遵循当地的基本金属丰度关系，具有较高的特定（质量归一化）的恒星形成率（SFR）的对象具有较低的金属丰度。此外，我们表明，在我们的样本中的星系躺在SFR- M_{*}关系（恒星形成的主序列）的外推。利用MZ关系和恒星形成的主要序列（并结合我们的数据与文献中更高的质量测量），我们测试模型，假设质量流入，流出和恒星形成之间的平衡。我们发现，外流需要描述的数据。通过比较不同的外流公式，我们发现动量驱动风可以描述MZ关系，但是，这个模型低估了低质量星系中恒星形成的数量。这种分歧可能表明，来自气体加热的预防性反馈被高估了，或者它可能意味着从平衡假设的一个更根本的偏差。

英文摘要：

We present abundance measurements from 26 emission-line selected galaxies at z~0.6-0.7. By reaching stellar masses as low as 10^8 M_{\sun}, these observations provide the first measurement of the intermediate redshift mass-metallicity (MZ) relation below 10^9 M_{\sun} For the portion of our sample above M > 10^9 M_{\sun} (8/26 galaxies), we find good agreement with previous measurements of the intermediate redshift MZ relation. Compared to the local relation, we measure an evolution that corresponds to a 0.12 dex decrease in oxygen abundances at intermediate redshifts. This result confirms the trend that metallicity evolution becomes more significant towards lower stellar masses, in keeping with a downsizing scenario where low mass galaxies evolve onto the local MZ relation at later cosmic times. We show that these galaxies follow the local fundamental metallicity relation, where objects with higher specific (mass-normalized) star formation rates (SFRs) have lower metallicities. Furthermore, we show that the galaxies in our sample lie on an extrapolation of the SFR-M_{*} relation (the star-forming main sequence). Leveraging the MZ relation and star-forming main sequence (and combining our data with higher mass measurements from the literature), we test models that assume an equilibrium between mass inflow, outflow and star formation. We find that outflows are required to describe the data. By comparing different outflow prescriptions, we show that momentum driven winds can describe the MZ relation; however, this model under-predicts the amount of star formation in low mass galaxies. This disagreement may indicate that preventive feedback from gas-heating has been overestimated, or it may signify a more fundamental deviation from the equilibrium assumption.

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