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arXiv 1910.04596astro-ph.GA
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不寻常的ISM在蓝色和尘埃气体丰富的镓(BADGRS)

The unusual ISM in Blue and Dusty Gas Rich Galaxies (BADGRS)

L. Dunne, Z. Zhang, P. de Vis, C. J. R. Clark, I. Oteo, S. J. Maddox, P. Cigan, G. de Zotti, H. L. Gomez, R. J. Ivison, K. Rowlands, M. W. L. Smith, P. van der … 展开作者

L. Dunne, Z. Zhang, P. de Vis, C. J. R. Clark, I. Oteo, S. J. Maddox, P. Cigan, G. de Zotti, H. L. Gomez, R. J. Ivison, K. Rowlands, M. W. L. Smith, P. van der Werf, C. Vlahakis, J. S. Millard

摘要:

Herschel-ATLAS对宇宙中冷尘埃的无偏巡天观测中发现了一个令人惊讶的非常蓝(FUV-K < 3.5)的星系群,这些星系富含尘埃,具有高气体分数(fHI = M_HI/(M*+M_HI)>0.5)。被称为“蓝色和尘埃气体丰富的来源”(BADGRS),它们具有冷的弥漫尘埃温度,以及本地宇宙中任何星系中最高的尘埃与恒星质量比。在这里,我们探索分子ISM在BADGRS的代表性样本,使用非常深的CO(J_up= 1,2,3)的观察在中央和外部磁盘区域。我们发现非常低的CO亮度(Tp=15-30 mK),尽管明亮的远红外发射和金属丰度在0.5<Z/Z_sun<1.0的范围内。CO线比率指示R_21=0.6-2.1和R_31=0.2-1.2的条件范围。利用金属丰度相关的CO光度到分子气体质量的转换,我们发现M_H2/M_d=7-27,Sigma_H2=0.5-6 M_sun pc^-2,比预期的低了一个数量级。BADGRS的分子气体耗尽时间尺度(τ_d = 0.5 Gyr)比其他本地螺旋星系低,与Kennicutt-Schmidt关系的偏移量与蓝致密矮星系相似。BADGRS中的冷弥漫尘埃温度(13-16 K)需要比从它们观测到的表面亮度推断的低10-20倍的星际辐射场。我们推测,在这些来源的尘埃要么有一个非常cluerical几何形状或一个非常不同的不透明度,以解释寒冷的温度和缺乏CO排放。BADGRS也有低的紫外线衰减,其紫外线颜色暗示SMC型尘埃衰减曲线,不同的恒星形成历史或不同的尘埃/恒星几何形状。它们位于与z=5星系相似的IRX-β空间中,可能是早期宇宙中高气体分数星系的局部类似物。

英文摘要:

The Herschel-ATLAS unbiased survey of cold dust in the local Universe is dominated by a surprising population of very blue (FUV-K < 3.5), dust-rich galaxies with high gas fractions (f_HI = M_HI/(M*+M_HI)>0.5)). Dubbed `Blue and Dusty Gas Rich Sources' (BADGRS) they have cold diffuse dust temperatures, and the highest dust-to-stellar mass ratios of any galaxies in the local Universe. Here, we explore the molecular ISM in a representative sample of BADGRS, using very deep CO(J_up=1,2,3) observations across the central and outer disk regions. We find very low CO brightnesses (Tp=15-30 mK), despite the bright far-infrared emission and metallicities in the range 0.5<Z/Z_sun<1.0. The CO line ratios indicate a range of conditions with R_21=0.6-2.1 and R_31=0.2-1.2. Using a metallicity dependent conversion from CO luminosity to molecular gas mass we find M_H2/M_d=7-27 and Sigma_H2=0.5-6 M_sun pc^-2, around an order of magnitude lower than expected. The BADGRS have lower molecular gas depletion timescales (tau_d = 0.5 Gyr) than other local spirals, lying offset from the Kennicutt-Schmidt relation by a similar factor to Blue Compact Dwarf galaxies. The cold diffuse dust temperatures in BADGRS (13-16 K) require an interstellar radiation field 10-20 times lower than that inferred from their observed surface brightness. We speculate that the dust in these sources has either a very clumpy geometry or a very different opacity in order to explain the cold temperatures and lack of CO emission. BADGRS also have low UV attenuation for their UV colour suggestive of an SMC-type dust attenuation curve, different star formation histories or different dust/star geometry. They lie in a similar part of the IRX-beta space as z=5 galaxies and may be useful as local analogues for high gas fraction galaxies in the early Universe.

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