The nature of the interstellar medium of the starburst low-metallicity galaxy Haro 11: a multi-phase model of the infrared emission
The nature of the interstellar medium of the starburst low-metallicity galaxy Haro 11: a multi-phase model of the infrared emission
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DOI：
10.1051/0004-6361/201219818
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发表时间：
2012-12-01
影响因子：
6.5
通讯作者：
Wu, R.
中科院分区：
文献类型：
--
作者：
Cormier, D.;Lebouteiller, V.;Wu, R.
上下文。低金属丰度星际介质（ISM）具有块状、低尘埃丰度和少量co示踪分子气体的特点，与普通星系有很大的不同。然而，附近宇宙中的许多矮星系正在积极地形成恒星。由于复杂的ISM相在空间上相互混合，因此需要进行详细的建模，以了解ISM的瓦斯涌出及其后续组成和结构。我们的目标是描述红外明亮低金属丰度星系Haro 11的多相ISM，解剖光电离和光解离气体成分。本文介绍了用Spitzer/IRS和Herschel/PACS光谱仪获得的中红外和远红外精细结构冷却线的观测结果。我们使用光谱合成代码Cloudy来系统地模拟产生这些谱线的电离气体和中性气体。我们发现中、远红外谱线约占L-TIR总红外光度的1%，是气体的主要冷却剂。哈罗11号正处于强烈的恒星形成阶段，如最亮的线所示，[O III] 88 μ m， L-[O III]/L- tir接近0.3%，[Ne III]/[Ne II]和[S IV]/[S III]的比率很高。由于它们的不同起源，观测线需要多相建模，包括：紧凑的HII区域，密集的碎片光解离区域（pdr），弥漫的扩展低电离/中性气体，其体积填充系数至少为90%，以及靠近恒星源的多孔热尘埃。为了更真实地描绘哈罗11号的ISM，我们需要对块状气源和气体结构进行建模。我们结合这4个模型分量解释了17条谱线的发射，通过谱能分布研究了星系的整体能量平衡，并建立了相质量清单。虽然Haro 11的离子发射谱线主要来自密集的H II区成分，但需要一种弥漫的低电离气体来解释[Ne II]、[N II]和[C II]谱线强度。我们的模型没有完全再现[O III] 88 μ m线强度，这暗示可能存在另一种低密度高电离介质。[O I]发射与低覆盖因子的致密PDR相一致，我们没有发现x射线主导成分的证据。PDR组分仅占[C II]排放量的10%。众所周知，在恒星形成区域的磁场很强，可能主导着PDR的压力。例如，对于100 μ G量级的场强，高达50%的[C II]发射可能来自PDR。
Context. The low-metallicity interstellar medium (ISM) is profoundly different from that of normal systems, being clumpy with low dust abundance and little CO-traced molecular gas. Yet many dwarf galaxies in the nearby universe are actively forming stars. As the complex ISM phases are spatially mixed with each other, detailed modeling is needed to understand the gas emission and subsequent composition and structure of the ISM.Aims. Our goal is to describe the multi-phase ISM of the infrared bright low-metallicity galaxy Haro 11, dissecting the photoionised and photodissociated gas components.Methods. We present observations of the mid-infrared and far-infrared fine-structure cooling lines obtained with the Spitzer/IRS and Herschel/PACS spectrometers. We use the spectral synthesis code Cloudy to methodically model the ionised and neutral gas from which these lines originate.Results. We find that the mid-and far-infrared lines account for similar to 1% of the total infrared luminosity L-TIR, acting as major coolants of the gas. Haro 11 is undergoing a phase of intense star formation, as traced by the brightest line, [O III] 88 mu m, with L-[O III]/L-TIR similar to 0.3%, and high ratios of [Ne III]/[Ne II] and [S IV]/[S III]. Due to their different origins, the observed lines require a multi-phase modeling comprising: a compact HII region, dense fragmented photodissociation regions (PDRs), a diffuse extended low-ionisation/neutral gas which has a volume filling factor of at least 90%, and porous warm dust in proximity to the stellar source. For a more realistic picture of the ISM of Haro 11 we would need to model the clumpy source and gas structures. We combine these 4 model components to explain the emission of 17 spectral lines, investigate the global energy balance of the galaxy through its spectral energy distribution, and establish a phase mass inventory. While the ionic emission lines of Haro 11 essentially originate from the dense H II region component, a diffuse low-ionisation gas is needed to explain the [Ne II], [N II], and [C II] line intensities. The [O III] 88 mu m line intensity is not fully reproduced by our model, hinting towards the possible presence of yet another low-density high-ionisation medium. The [O I] emission is consistent with a dense PDR of low covering factor, and we find no evidence for an X-ray dominated component. The PDR component accounts for only 10% of the [C II] emission. Magnetic fields, known to be strong in star-forming regions, may dominate the pressure in the PDR. For example, for field strengths of the order of 100 mu G, up to 50% of the [C II] emission may come from the PDR.