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的结构中,形成和星系演变

该 study of galaxy formation and evolution aims to address the basic question of how the Milky Way and other types of galaxy we see around us today came to be. This not only involves understanding the properties of nearby galaxies in great detail, but also looking into the very distant Universe, since the long light travel times from distant galaxies allow us to examine the properties of galaxies at different times in the past. This way we can build up an empirical picture of how they have evolved over cosmic time and compare this to numerical models.

一些我们试图回答的关键问题是:

  • 什么是恒星形成和黑洞成长的宇宙历史以及它如何依赖于基本属性如质量?
  • 什么是恒星形成早期宇宙的性质是什么?
  • 不要星系是如何采集和处理他们的气?
  • 如何影响环境星系演化?
  • 如何反馈(由恒星和黑洞的生长)影响星系演化?

在汽车星系形成和演化的研究涵盖了一系列的在这些主题的触摸区域来,和我们的工作人员的强大的团队,研究员博士后和学生都从事不同的项目。

星系的结构

(布林克斯)

结构在中性ISM

One of the key scientific drivers for embarking on the THINGS project is the desire to understand the fine scale structure of the interstellar medium (ISM) and how this varies as a function of galaxy (Hubble) type, metallicity, star formation rate, etc. Previous studies have shown that massive stars, via their stellar winds and as a result of them exploding subsequently as a supernova, can shape their immediate surrounding. Because massive stars form usually in clusters, these effects accumulate and large, coherent structures can form in the ISM. 该se structures, in principle expanding bubbles of coronal gas, reveal themselves in 21-cm maps of neutral, atomic gas as expanding shells or holes. One of the aims of THINGS is to relate porosity of the ISM as traced by the HI structures to current and past star formation, to determine the energy balance in the ISM, to link this to the observed velocity dispersion and characteristics of turbulence in spiral galaxies, and lastly how swept up material in these expanding shells can trigger subsequent generations of star formation. Figure 1 is an illustration of the rich structure in the form of HI shells and bubbles in the ISM of two THINGS targets, NGC 6946 and NGC 3184.

NGC 6945 and NGC 3184 visual

图1:VLA喜(红色)和表示这两个不同波长看到的ISM的结构之间的相关性惊人斯皮策太空望远镜8层μ的地图(绿色)的比较。

supershell引起恒星形成

THINGS clearly demonstrates that the ISM is dominated by giant shells and supershells, ranging in size from the resolution limit to up to kpc size. 该 most widely accepted view on how these shells form is that the combined effects of stellar winds and supernovae originating in an OB association or super star cluster (SSC) deposit vast amounts of energies within a small volume over a short time interval resulting in a pressure-driven, expanding shell. GMCs can form within the accumulation front of shells and supershells. From recent CO maps (LMC, SMC, IC10) there is now growing evidence that GMCs do indeed form on the expanding rims of shells, or within the interface where two expanding shells run into each other (see Figure 2).

IRAM高原日布雷观察已经分配共同详细研究在某些事情上目标的几个小区域相对于喜贝壳和supershells调查的GMC的相对位置。

Column density map

图2:共柱密度图(蓝色)覆盖在VLA喜地图(红色)上。共迹线冷,分子氢,这是很可能下自身重力崩塌,并产生分即区域。注意到这些地区如何似乎集中在喜壳的边缘。

星系的外边缘

螺旋星系认为具有良好定义的边界。在磁盘上的原子的中性氢气的21厘米波长观察揭示两个重要的事实:喜磁盘超出它们的光学同行远延伸,并且它们正在急剧截断。在文献中这已被归因于河外辐射场充当中性气体盘的最外的到达离子化剂。

基于观察到的作为东西调查的一部分9周的星系的分析,我们发现,最外面的喜结构保持在接近恒定的1020至1021年原子厘米-2〜然后迅速翻身。这个翻身发生在列密度水平被认为过高河外辐射场有任何严重影响。相反,观察到似乎朝向具有良好限定的边缘的星系,因为它们简单地用完重子材料的点。这个断言通过文献中仿真支持。

HI surface density

图3:左:集成的NGC 3198右表面喜密度图谱:沿着10" 分辨率北半长轴喜柱密度分布的基础上,新的东西数据(灰色符号),相比于较旧的低分辨率VLA数据(黑色符号)

小东西

The study of HI in large spirals is now being extended to dwarf galaxies in a survey known as 小东西, to probe the low-mass, low-metallicity regime. It is expected that several of the relations found or confirmed in big spirals will break down in that low-mass regime. An example of such a relation is the Far Infrared, radio continuum relation (FIR-RC, for short). Brinks and co-workers are engaged in a multi-band radio continuum study of several dwarf galaxies. 该y have created the deepest radio continuum images to date at C-band (5 GHz), reaching down to 6 µJy.

Spitzer

图4:左:C波段(5 GHz)的无线电覆盖的连续作为斯皮策24μm图像是最近,大质量恒星形成的示踪上的轮廓。右:同左面板而是表示L波段(1.5千兆赫)的轮廓。

亚毫米波调查

(考平,geach,史蒂文斯,史密斯,哈德卡斯尔)

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Herschel-ATLAS is the largest open time extragalactic survey that was conducted with the Herschel 空间 Observatory, and has detected around 250,000 galaxies based on their dust content alone, from the local Universe out to the highest redshifts. To date, the survey has produced in excess of 50 refereed publications, many led from CAR, on a diverse range of topics from studying the properties of dust in galaxies (e.g. Dunne et al. 2010, Smith et al. 2013), their star formation histories, stellar masses and multi-wavelength properties (e.g. Smith et al. 2012, 2014, Jarvis et al. 2010, Rowlands et al. 2014, Davis et al. 2015), studying the relationship between star formation and AGN (e.g. Hardcastle et al. 2010, 2013, Bonfield et al. 2011, Kalfountzou et al. 2014, Gurkan et al. 2015), linking galaxy properties to their merger history (e.g. Kaviraj et al. 2013) and environments (e.g. Coppin et al. 2011, Burton et al. 2013), and finding large samples of lensed galaxies (Negrello et al. 2010).

Pachromatic SED

从Smith等全色SEDS。 (2012),在H-图谱使用恒星形成星系导出的;根据具体的恒星形成率分级,和垂直偏移,这些经验模板比其它可用的模型冷却器,和包括不确定性与波长的所述第一时间的函数。

所述MJY成像VLBA勘探(mjive-20)的调查

(卡维拉杰)

mJIVE-20 is the largest radio VLBI survey to date, which has used the Very Large Baseline Array (VLBA) to observe 30,000 galaxies detected by the FIRST radio survey, with around 5000 detections. The >10^7 K brightness temperature required for an mJIVE detection cannot be achieved via star-formation alone, which enables us to unambiguously detect nearby radio AGN and study their role in galaxy evolution. 在一个n ongoing series of papers, we are using mJIVE-20 to explore the characteristics of radio AGN in the nearby Universe, the processes that trigger them and their impact on star formation. 该 unambiguous nature of AGN detection using VLBI enables us to put better constraints on these key questions than has been possible in the past.

我们最近的工作 has shown that AGN in low-density environments are triggered primarily by mergers, and that AGN activity peaks several dynamical timescales after the peak of the associated star formation. This time delay implies that the AGN, on average, couples to the gas reservoir only after much of it has been depleted by star formation. Thus, since it impacts only residual gas, the AGN cannot strongly regulate the bulk of the starburst. Thus, while evidence for AGN feedback is strong in dense regions of the Universe (e.g. in central cluster galaxies where the gas is obtained by direct cooling from the hot halo), the role of the AGN in regulating star formation in the typical star forming galaxy is likely to be insignificant in the local Universe. This has strong implications for the way AGN feedback is incorporated in galaxy formation models at low redshift.

在一个 配套文件 we have used mJIVE-20 to study the relatively rare population of AGN in late-type (spiral) galaxies that have nuclear radio luminosities similar to that in their early-type counterparts. We have shown that the AGN population in late-type galaxies is preferentially hosted by spirals that have high stellar masses, red colours, low star formation rates and are involved in interactions, with little dependence on the detailed morphology or local environment of the host galaxy. Furthermore, like in early-type galaxies, the onset of the AGN lags behind the peak of the star formation. 该 time delay between AGN activity and star formation is therefore a ubiquitous feature of galaxy evolution in general.

在这一系列的最新论文 500 Internal Server Error

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在早期的WFC3释科学计划和candels(宇宙组装近红外深河外星系遗产调查)

(卡维拉杰)

The study of the distant Universe has been revolutionised by the advent of high-resolution near-infrared imaging on the HST via the recently installed Wide Field Camera 3 (WFC3). We are involved in two key programmes that have exploited the novel capabilities of the WFC3. The first is the WFC3 Early-Release Science (ERS) programme, which was a 210-orbit HST programme designed to demonstrate the WFC3's capabilities to the astronomical community. 该 WFC3-ERS was a precursor to CANDELS, the largest HST legacy programme to date, which has used the WFC3 to image the early Universe in the near-infrared wavelengths across almost 2 square degrees of sky.

We have used these surveys to explore the processes that drive star formation and morphological transformation in the early Universe. 该se studies have shown that today's massive spheroids likely formed the bulk of their stellar mass over short timescales (<1 Gyr) in the redshift range 2这项工作

indicates that the creation of spheroids is dominated by processes  (e.g. minor-merger-triggered disk instabilities) other than major mergers.

A 配套文件 has probed the significance of major mergers in driving star formation in the early Universe. Using a well-defined sample of massive galaxies we have employed visually-classified morphologies from rest-frame V-band HST imaging to split the cosmic star formation budget at z~2 by morphological class. More than half the budget in hosted by late-type galaxies that show no signs of interactions, with only around 27 per cent in major mergers. However, given that a system undergoing a major merger will continue to experience star formation driven by other processes at this epoch (e.g. cold accretion and minor mergers), 27 per cent is an upper limit to the major-merger contribution to star formation activity at this epoch. 该 ratio of the average specific star formation rate in major mergers to that in the non-interacting late types is around 2:1, suggesting that the enhancement of star formation due to major merging is typically modest, and that just under half the star formation in systems experiencing major mergers is unrelated to the merger itself. Taking this into account, the actual major-merger contribution to the star formation budget is likely to be as low as 15 per cent. Taken together, these studies indicate that the major merger process is an insignificant player in galaxy evolution around the epoch of peak cosmic star formation.