KMS of Xinjiang Astronomical Observatory, CAS
| 近邻星系的冷尘埃性质和亚毫米辐射超研究 | |
| Alternative Title | Investigating the cold dust properties and submillimeter excess of Nearby Galaxies |
常正雪
| |
| Subtype | 博士 |
| Thesis Advisor | 周建军 |
| 2021-06-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Name | 理学博士 |
| Degree Discipline | 天体物理 |
| Keyword | 近邻星系 星际尘埃 SED 亚毫米辐射超 |
| Abstract | 星系的形成与演化是现代天体物理学中最基本和重要的科学研究之一。而研究尘埃辐射可以有效地追踪被尘埃遮挡的恒星形成活动，是了解星系如何演化的有效途径。尘埃辐射主要集中在红外到亚毫米的波段范围。而星际尘埃的主导部分是处于冷状态的尘埃成分，我们称之为“冷尘埃”。该成分主要辐射在? > 100 ?m的远红外到亚毫米波段范围。研究尘埃辐射在红外波段的光谱能量分布（SED）可以得到尘埃的性质以及其随星系环境而发生的变化，进而可以揭示星系中发生的物理过程。我们分别从NGLS（The JCMT Nearby Galaxies Legacy Survey）和DustPedia项目中选出13个近邻旋涡星系和12个近邻矮不规则星系，使用从中红外到亚毫米波段的数据研究这些星系的冷尘埃辐射，搜寻可能存在的亚毫米辐射超和探索在哪些情况下亚毫米辐射超容易发生。在近邻旋涡星系的研究中，我们使用一个具有双温度尘埃成分的黑体模型（2MBB模型），并结合蒙特卡洛方法，从星系的全局角度逐个对每个星系进行中红外到亚毫米波段范围（22 − 500 ?m）的SED拟合，获得了冷尘埃的温度、质量等参数。研究发现：（1）星系样本的冷尘埃温度与冷尘埃辐射指数（?c）之间存在反相关假象。（2）冷尘埃质量随着星系的红外总光度的变弱而增加。（3）基于 ?c = 2 的2MBB模型，NGC 2976、NGC 3351和NGC 4631表现出850 ?m辐射超。此辐射超与非尘埃辐射（CO(3−2) 线辐射、自由-自由辐射和同步辐射）无关。我们讨论了850 ?m流量的观测值与模型推测值之间的差异如何随冷尘埃性质或星系特征变化。结果表明：（1）冷尘埃温度越低，850 ?m辐射强度越大。（2）对于红外总光度较弱并且冷尘埃质量较低的星系来说，850 ?m辐射超可能更容易被探测到。（3）在具有较低的恒星总质量的星系中很容易发生850 ?m辐射超。（4）当星系的金属丰度变贫时，850 ?m辐射超更加明显。基于?c = 2的2MBB模型，我们使用层级贝叶斯方法对12个近邻矮不规则星系进行三个波段范围（22−250 ?m、22−350 ?m 和 22−500 ?m）的全局SED拟合，目的是探测350、500 和850 ?m波段可能存在的辐射超和研究冷尘埃的性质。结果显示没有星系存在350 ?m辐射超；一个星系存在500 ?m辐射超；九个星系存在850 ?m辐射超，并且其中五个星系在?c设置为自由参数时仍然表现出850 ?m辐射超。在矮不规则星系样本中：（1）对于恒星形成活动不活跃的星系，850 ?m辐射超容易被探测到。（2）对于具有越低的分子氢气体质量比或者越低的冷尘埃质量与气体质量比的星系，其850 ?m辐射超的探测率越高。（3）随着星系的演化，原子氢气体质量比会降低，850 ?m辐射超趋于减少甚至会消失。研究结果还表明，更多长波段的亚毫米数据加入SED拟合可以更准确地测量冷尘埃温度和冷尘埃质量。随着星系的恒星形成越激烈或者金属丰度越富，冷尘埃温度会升高。冷尘埃质量与恒星总质量之比（Md /M∗）与星系的比恒星形成率之间存在微弱的反相关关系。 |
| Other Abstract | To understand how the galaxies form and evolve is one of the key and fundamental scientific study of modern astrophysics. It is an effective way to understand how galaxies evolve to study the dust emission which can effectively trace the star formation activity obscured by dust grains. Dust radiates mainly in the infrared to submillimeter (submm) band range. Most of dust emission comes from the cold phase, called “cold dust”, which mainly radiates in far infrared to submm bands at wavelengths 𝜆 > 100 𝜇m. Studying the spectral energy distribution (SED) of dust emission at the infrared bands can obtain the properties of the dust and its changes with the environment of galaxy, and then reveal the physical processes occurring in the galaxy. We selected 13 nearby spiral galaxies and 12 nearby dwarf irregular galaxies from the NGLS (The JCMT Nearby Galaxies Legacy Survey) and Dustpedia projects, respectively, and used data from mid-infrared to submm to study the cold dust properties of these galaxies, probe possible submm excess emission and explore under which situation the submm excess occurs easily. In the study of nearby spiral galaxies, we used a two-temperature modified black-body model (2MBB model) and combined with the Monte Carlo method to perform SED fits using the data from the mid-infrared to submm bands (24 − 500 𝜇m) for each spiral galaxy from a global perspective. The parameters (such as cold dust temperature, mass and so on) are obtained. It is found that: (1) there is an artificial inverse correlation between the cold dust temperature and cold dust emission index (𝛽c ) for the galaxies. (2) The cold dust mass increases with the decreasing total infrared luminosity of the galaxy. (3) NGC 2976, NGC 3351, and NGC 4631 show 850 𝜇m excess emission based on the 2MBB model with 𝛽c = 2. Such excess emission is independent of non-dust emission (CO(3 − 2) line emission, free-free emission and synchrotron emission). We discussed how the difference between the observed and modelled flux at 850 𝜇m varies with cold dust properties or galactic characteristics. The results show that: (1) The lower the temperature of cold dust is, the stronger the excess emission is at 850 𝜇m. (2) For galaxies with lower total infrared luminosity and lower mass of cold dust, 850 𝜇m excess emission may be more easily detected. (3) The 850 𝜇m excess is more likely to occur in galaxies with low total stellar mass. (4) When the metallicity of the galaxy becomes poor, the 850 𝜇m excess becomes more obvious. Based on the 2MBB model with 𝛽c = 2, we used the hierarchical Bayesian method to perform global SED fitting for 12 nearby dwarf irregular galaxies in three data ranges (22−250 𝜇m, 22−350 𝜇m, and 22−500 𝜇m) to probe possible excesses at 350, 500 and 850 𝜇m and study the properties of cold dust. The results show that there is no 350 𝜇m excess emission in the galaxies. A galaxy has an excess at 500 𝜇m. Nine galaxies show 850 𝜇m excess emission, and five of them still show 850 𝜇m excess emission even when 𝛽c is free. In our sample of dwarf irregular galaxies: (1) 850 𝜇m excess emission is more likely to detect for galaxies that are not active in star formation. (2) The lower the molecular hydrogen gas mass fraction or the lower ratio of the cold dust mass and gas mass of the galaxies is, the higher the detection rate of 850 𝜇m excess emission is. (3) With the evolution of the galaxy, the atomic hydrogen gas mass fraction decreases, the 850 𝜇m excess tends to decrease or even disappear. The results also show that SED fitting with submm data of more longer wavelength can more accurately measure cold dust temperature and cold dust mass. As star formation in galaxies becomes more intense or metallicity becomes richer, the cold dust temperatures tends to rise. There is a weak inverse correlation between the ratio of cold dust mass to total stellar mass (Md /M∗ ) and the specific star formation rate. |
| Pages | 122 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4732 |
| Collection | 研究生学位论文 |
| Affiliation | 中国科学院新疆天文台 |
| First Author Affilication | Xinjiang Astronomical Observatory, Chinese Academy of Sciences |
| Recommended Citation GB/T 7714 | 常正雪. 近邻星系的冷尘埃性质和亚毫米辐射超研究[D]. 北京. 中国科学院大学,2021. |
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