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arXiv 2009.10085astro-ph.GA
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MOSDEF巡天:首次直接测量高红移星云尘埃衰减曲线

The MOSDEF Survey: The First Direct Measurements of the Nebular Dust Attenuation Curve at High Redshift

Naveen A. Reddy, Alice E. Shapley, Mariska Kriek, Charles C. Steidel, Irene Shivaei, Ryan L. Sanders, Bahram Mobasher, Alison L. Coil, Brian Siana, William R. F… 展开作者

Naveen A. Reddy, Alice E. Shapley, Mariska Kriek, Charles C. Steidel, Irene Shivaei, Ryan L. Sanders, Bahram Mobasher, Alison L. Coil, Brian Siana, William R. Freeman, Mojegan Azadi, Tara Fetherolf, Gene Leung, Sedona H. Price, Tom Zick

摘要:

我们使用一个样本的532恒星形成星系的红移$z\sim 1.4-2.6$深静止帧光谱的MOSFIRE深演化场(MOSDEF)调查放置在高红移的星云衰减曲线的第一个约束。基于在这些星系的合成光谱中检测到的前五条低阶Balmer发射线(${\rm Hα}$到${\rm Hε}$),我们得到了一条形状与银河系消光曲线相似的星云衰减曲线,这表明在高红移的大质量恒星的视线上,尘埃覆盖率和吸收/散射特性与银河系的平均视线相似。这里推导出的曲线意味着星云红化值平均系统地大于恒星连续体推导出的值。在包含恒星多样性效应的恒星星族合成模型中,星云线和恒星连续体红化的差异可能意味着分子云穿越时间尺度比局部分子云长$\gtrsim 3\times$倍,恒星形成速率恒定或随时间增加,使得新形成的和更尘埃的OB协会总是主导电离通量,和/或使星云发射变红的尘埃可能与非分子(即,电离和中性)阶段。我们的分析指出,各种调查的星云衰减曲线,将启用下一代的地面和空间为基础的设施。

英文摘要:

We use a sample of 532 star-forming galaxies at redshifts $z\sim 1.4-2.6$ with deep rest-frame optical spectra from the MOSFIRE Deep Evolution Field (MOSDEF) survey to place the first constraints on the nebular attenuation curve at high redshift. Based on the first five low-order Balmer emission lines detected in the composite spectra of these galaxies (${\rm Hα}$ through ${\rm Hε}$), we derive a nebular attenuation curve that is similar in shape to that of the Galactic extinction curve, suggesting that the dust covering fraction and absorption/scattering properties along the lines-of-sight to massive stars at high redshift are similar to those of the average Milky Way sightline. The curve derived here implies nebular reddening values that are on average systematically larger than those derived for the stellar continuum. In the context of stellar population synthesis models that include the effects of stellar multiplicity, the difference in reddening of the nebular lines and stellar continuum may imply molecular cloud crossing timescales that are a factor of $\gtrsim 3\times$ longer than those inferred for local molecular clouds, star-formation rates that are constant or increasing with time such that newly-formed and dustier OB associations always dominate the ionizing flux, and/or that the dust responsible for reddening the nebular emission may be associated with non-molecular (i.e., ionized and neutral) phases of the ISM. Our analysis points to a variety of investigations of the nebular attenuation curve that will be enabled with the next generation of ground- and space-based facilities.

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