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z=4.05时发光原星系团星系中的尘埃和气体：正常星系和星暴星系中不同宇宙尘埃演化的情况

Dust and gas in luminous proto-cluster galaxies at z=4.05: the case for different cosmic dust evolution in normal and starburst galaxies

Qinghua Tan, Emanuele Daddi, Georgios Magdis, Maurilio Pannella, Mark Sargent, Dominik Riechers, Matthieu Béthermin, Frédéric Bournaud, Chris Carilli, Elisabete… 展开作者

Qinghua Tan, Emanuele Daddi, Georgios Magdis, Maurilio Pannella, Mark Sargent, Dominik Riechers, Matthieu Béthermin, Frédéric Bournaud, Chris Carilli, Elisabete da Cunha, Helmut Dannerbauer, Mark Dickinson, David Elbaz, Yu Gao, Jacqueline Hodge, Frazer Owen, Fabian Walter

备注：
17 pages, 9 figures. Updated to A&A accepted version
发表信息：
A&A 569, A98 (2014)
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摘要：

利用新的IRAM Plateau de Bure干涉仪（PdBI）CO（4-3）和1.2-3.3 mm连续谱观测，在$z=4.05$测量了GN 20原星系团中三个亚毫米星系的尘埃和气体含量。所有这三个SMG都被严重的尘埃遮蔽，基于紫外线的恒星形成率（SFR）估计值明显小于来自热红外（IR）的估计值，这与HST和CO成像显示的空间偏移一致。还基于特定的SFR，CO-到-H $_2$转换因子和气体耗尽时标的评估，我们将所有三个星系归类为星爆（SB），虽然GN20.2 b的置信度较低，这可能是后期的合并事件。我们把我们的测量的背景下，主序星（MS）和SB星系的演化特性。ULIRGs的$L'_{\rm CO}/M_{\rm dust}$和$M_{\rm dust}/M_\star$比率比$z=0$ MS星系大3-5倍，但通过$z\sim2$，差异似乎变得模糊，可能是由于不同的金属丰度演化。SB星系的$L'_{\rm CO}/M_{\rm dust}$和$M_{\rm dust}/M_\star$比率似乎一直缓慢地演化到$z>6$（与SB事件的快速富集一致），而MS星系的$M_{\rm dust}/M_\star$从$z=0$迅速增加到2（由于气体分数增加，由金属丰度的减少补偿）。虽然没有IR/submm连续检测是无可争议的正常的大质量星系在$z>2.5$，我们表明，如果金属丰度确实迅速下降，这些系统在$z>3$在文献中声称，我们应该期待一个强烈的下降，其$M_{\rm dust}/M_\star$，与最近的PdBI和ALMA上限一致。我们的结论是，$M_{\rm dust}/M_\star$比率可能是一个强大的工具，区分恒星爆发和正常星系在$z>4$。

英文摘要：

We measure the dust and gas content of the three sub-millimeter galaxies (SMGs) in the GN20 proto-cluster at $z=4.05$ using new IRAM Plateau de Bure interferometer (PdBI) CO(4-3) and 1.2-3.3 mm continuum observations. All these three SMGs are heavily dust obscured, with UV-based star formation rate (SFR) estimates significantly smaller than the ones derived from the bolometric infrared (IR), consistent with the spatial offsets revealed by HST and CO imaging. Based also on evaluations of the specific SFR, CO-to-H$_2$ conversion factor and gas depletion timescale, we classify all the three galaxies as starbursts (SBs), although with a lower confidence for GN20.2b that might be a later stage merging event. We place our measurements in the context of the evolutionary properties of main sequence (MS) and SB galaxies. ULIRGs have 3-5 times larger $L'_{\rm CO}/M_{\rm dust}$ and $M_{\rm dust}/M_\star$ ratios than $z=0$ MS galaxies, but by $z\sim2$ the difference appears to be blurred, probably due to differential metallicity evolution. SB galaxies appear to slowly evolve in their $L'_{\rm CO}/M_{\rm dust}$ and $M_{\rm dust}/M_\star$ ratios all the way to $z>6$ (consistent with rapid enrichment of SB events), while MS galaxies rapidly increase in $M_{\rm dust}/M_\star$ from $z=0$ to 2 (due to gas fraction increase, compensated by a decrease of metallicities). While no IR/submm continuum detection is available for indisputably normal massive galaxies at $z>2.5$, we show that if metallicity indeed decrease rapidly for these systems at $z>3$ as claimed in the literature, we should expect a strong decrease of their $M_{\rm dust}/M_\star$, consistent with recent PdBI and ALMA upper limits. We conclude that the $M_{\rm dust}/M_\star$ ratio could be a powerful tool for distinguishing starbursts from normal galaxies at $z>4$.

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