Dust and gas in luminous proto-cluster galaxies at z=4.05: the case for different cosmic dust evolution in normal and starburst galaxies
Dust and gas in luminous proto-cluster galaxies at z=4.05: the case for different cosmic dust evolution in normal and starburst galaxies
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DOI：
10.1051/0004-6361/201423905
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发表时间：
2014-03
影响因子：
6.5
通讯作者：
Q. Tan;E. Daddi;G. Magdis;M. Pannella;M. Sargent;D. Riechers;M. B'ethermin;F. Bournaud;C. Carilli;E. D. Cunha;H. Dannerbauer;M. Dickinson;D. Elbaz;Yu Gao;J. Hodge;F. Owen;F. Walter
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文献类型：
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作者：
Q. Tan;E. Daddi;G. Magdis;M. Pannella;M. Sargent;D. Riechers;M. B'ethermin;F. Bournaud;C. Carilli;E. D. Cunha;H. Dannerbauer;M. Dickinson;D. Elbaz;Yu Gao;J. Hodge;F. Owen;F. Walter
利用IRAM Plateau de Bure干涉仪（PdBI）CO（4-3）和1.2-3.3mm连续谱观测方法，测量了GN 20原星系团中3个z=4.05的亚毫米星系（SMG）的尘埃和气体含量。所有这三个SMG都被严重的尘埃遮蔽，基于紫外线的星星形成率（SFR）估计显着小于来自热红外，与HST和CO成像显示的空间偏移一致。还基于特定的SFR，CO到H2的转换因子和气体耗尽时间尺度的评估，我们将所有三个星系归类为星爆（SB），虽然GN20.2b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′CO/M dust和M dust/M dust比z=0 MS星系大3-5倍，但到z = 2时，这种差异似乎变得模糊，可能是由于不同的金属丰度演化。SB星系的L′CO/M dust和M dust/M dust比值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 dust/M dust比值从z=0到2迅速增加（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的文献中所声称的，我们应该期待一个强烈的减少，其M dust/M dust，符合最近的PdBI和阿尔马上限。我们得出的结论是，Mdust/M比可能是区分z>4的星暴与正常星系的有力工具。
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 1.2-3.3mm 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 IR, consistent with the spatial offsets revealed by HST and CO imaging. Based also on evaluations of the specific SFR, CO-to-H2 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′CO/Mdust and Mdust/M⋆ ratios than z=0 MS galaxies, but by z∼2 the difference appears to be blurred, probably due to differential metallicity evolution. SB galaxies appear to slowly evolve in their L′CO/Mdust and Mdust/M⋆ ratios all the way to z>6 (consistent with rapid enrichment of SB events), while MS galaxies rapidly increase in Mdust/M⋆ 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 Mdust/M⋆, consistent with recent PdBI and ALMA upper limits. We conclude that the Mdust/M⋆ ratio could be a powerful tool for distinguishing starbursts from normal galaxies at z>4.