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arXiv 2405.04582astro-ph.GA
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对一个低质量、高遮蔽 z=4.27 主序星系星际介质条件的首批约束

First Constraints on the ISM Conditions of a Low Mass, Highly Obscured z=4.27 Main Sequence Galaxy

Andrew Mizener, Alexandra Pope, Jed McKinney, Patrick Kamieneski, Katherine E. Whitaker, Andrew Battisti, Eric Murphy

AI总结:

本文利用 ALMA 对强透镜 z=4.273 低质量高遮蔽星系 MACSJ0717 Az9 进行 CO、[N II] 与连续谱分析,约束其分子气体、PDR、尘埃质量及旋转盘运动学,指出其遮蔽阶段可能较长。

摘要:

我们展示了 MACSJ0717 Az9 的分子气体含量和星际介质(ISM)条件;这是一个强引力透镜的 z=4.273、恒星质量 M_* ≈ 2×10^9 M⊙ 的恒星形成星系,具有异常高(约80%)的遮蔽恒星形成比例。我们利用 ALMA 在两个独立的透镜像中探测到 CO(4-3),并探测到 [N II]205 μm。我们得到分子气体质量 log10[M_H2 (M⊙)] = 9.77,这使其相对于较低红移的气体比例标度关系而言分子气体适度匮乏。借助光解离区(PDR)模型,我们将 CO(4-3) 测量与已有的 [C II]158 μm 谱线及总红外光度测量相结合,对 PDR 条件进行建模。我们发现其 PDR 条件与近邻恒星形成星系相似,平均氢密度为 log10[n_H cm^-3] = 4.80±0.39,平均辐射场强度为 log10[G0 Habing] = 2.83±0.26。基于 Band 3 连续谱数据,我们得到内禀尘埃质量上限 log10[M_dust (M⊙)] < 7.73,与已有估计一致。我们使用三维倾斜环模型拟合代码 3D-Barolo 来确定 CO(4-3) 发射气体的运动学性质。我们发现其由旋转主导,V/σ = 4.6±1.7,与 [C II] 的运动学一致。由于 Az9 的 PDR 条件与 z~0.2 的普通尘埃恒星形成星系显著相似,并且具有稳定的分子盘,我们的观测表明,z~4 低质量星系的尘埃遮蔽阶段持续时间相对较长。因此,Az9 可能代表了一个更广泛存在的星系群体,而该群体因现有毫米波巡天深度不足而被遗漏。

英文摘要:

We present the molecular gas content and ISM conditions of MACSJ0717 Az9, a strong gravitationally lensed $z=4.273$, $M_{*} \simeq 2\times10^9M_{\odot}$ star-forming galaxy with an unusually high ($\sim 80\%$) obscured star formation fraction. We detect CO(4-3) in two independent lensed images, as well as [N II]205$μ$m, with ALMA. We derive a molecular gas mass of log$_{10}[M_{H_{2}} (M_{\odot})] = 9.77$ making it moderately deficient in molecular gas compared to the lower redshift gas fraction scaling relation. Leveraging photodissociation region (PDR) models, we combine our CO(4-3) measurements with existing measurements of the [C II] 158$μ$m line and total infrared luminosity to model the PDR conditions. We find PDR conditions similar to local star-forming galaxies, with a mean hydrogen density log$_{10}$[$n_H$ $cm^{-3}$] = $4.80\pm0.39$ and a mean radiation field strength log$_{10}$[G$_0$ Habing] = $2.83\pm0.26$. Based on Band 3 continuum data, we derive an upper limit on the intrinsic dust mass of log$_{10}[M_{\rm dust} (M_{\odot})] < 7.73$, consistent with existing estimates. We use the 3D tilted-ring model fitting code 3D-Barolo to determine the kinematic properties of the CO(4-3) emitting gas. We find that it is rotationally dominated, with a $V/σ=4.6 \pm 1.7$, consistent with the kinematics of the [C II]. With PDR conditions remarkably similar to normal dusty star-forming galaxies at z ~ 0.2 and a stable molecular disk, our observations of Az9 suggest that the dust-obscured phase for a low-mass galaxy at z$\sim$4 is relatively long. Thus, Az9 may be representative of a more widespread population that has been missed due to insufficiently deep existing millimeter surveys.

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