旧版网站 台内地址簿 网站地图 联系我们 English 中国科学院
首页紫台简介机构设置新闻动态科研成果研究队伍合作交流天文学院创新文化党群园地信息公开
新闻动态
图片新闻
综合新闻
天文快讯
Colloquium & 学术交流
国内外天文学术会议
紫台通讯
传媒扫描
科普动态
科研信息
台内新闻
您当前的位置:首页>新闻动态>Colloquium & 学术交流
9月22日 Physical conditions of the interstellar medium in high-redshift submillimetre bright galaxies
2017年09月21日

  报告题目:Physical conditions of the interstellar medium in high-redshift submillimetre bright galaxies

  报告人:杨辰涛(中国科学院大学与巴黎十一大联合培养博士答辩)

  摘要:The discovery of a population of high- redshift dust-obscured submillimeter galaxies (SMGs) from ground-based submm cameras has revolutionised our understanding of galaxy evolution and star formation in extreme conditions. They are the strongest starbursts in the Universe approaching the Eddington limit and are believed to be the progenitors of the most massive galaxies today. However, theoretical models of galaxy evolution have even been challenged by a large number of detections of high-redshift SMGs. A very few among them are gravitationally lensed by an intervening galaxy. Recent wide-area extragalactic surveys have discovered hundreds of such strongly lensed SMGs, opening new exciting opportunities for observing the interstellar medium in these exceptional objects.

  We have thus carefully selected a sample of strongly gravitational lensed SMGs based on the submillimeter flux limit from the Herschel-ATLAS sample. Using IRAM telescopes, we have built a rich H2O-line-detected sample of 16 SMGs. We found a close-to-linear tight correlation between the H2O line and total infrared luminosity. This indicates the importance of far-IR pumping to the excitation of the H2O lines. Using a far-IR pumping model, we have derived the physical properties of the H2O gas and the dust. We showed that H2O lines trace a warm dense gas that may be closely related to the active star formation. Along with the H2O lines, several H2O+ lines have also been detected in three of our SMGs. We also find a tight correlation between the luminosity of the lines of H2O and H2O+ from local ULIRGs to high-redshift SMGs. The flux ratio between H2O+ and H2O suggests that cosmic rays from strong star forming activities are possibly driving the related oxygen chemistry.

  Another important common molecular gas tracer is the CO line. We have observed multiple transitions of the CO lines in each of our SMGs with IRAM 30m telescope. By analysing the CO line profile, we discovered a significant differential lensing effect that might cause underestimation of the linewidth by a factor of ~ 2. Using LVG modeling and fitting the multi-J CO fluxes via a Bayesian approach, we derived gas densities and temperature, and CO column density per unit velocity gradient. We then found a correlation between the gas thermal pressure and the star formation efficiency. We have also studied the global properties of the molecular gas and its relationship with star formation. We have derived the gas to dust mass ratio and the gas depletion time, they show no difference compared with other SMGs. With the detections of atomic carbon lines in our SMGs, we extended the local linear correlation between the CO and CI line luminosity. Finally, we compared the line widths of the CO and H2O emission line, which agree very well with each other. This suggests that the emitting regions of these two molecules are likely to be co-spatially located.

  In order to understand the properties of molecular emission in high-redshift SMGs, and more generally, the structure and the dynamical properties of these galaxies, it is crucial to acquire high-resolution images. We thus observed two of our brightest sources with ALMA and NOEMA interferometers using their high spatial resolution configuration. These images have allowed us to reconstruct the intrinsic morphology of the sources. We compared the CO, H2O and dust emission. The cold dust emission has a smaller size compared with the CO and H2O gas, while the latter two are similar in size. By fitting the dynamical model to the CO data of the source, we have shown that the source can be modelled with a rotating disk. We derived the projected dynamical mass and the effective radius of those sources.With the future NOEMA and ALMA, we will be able to extend such kind of observations to a larger sample lensed SMGs and even to unlensed SMGs, to study various gas tracers, and to understand the physical conditions of the ISM and their relation to the star formation.

  报告时间:9月22日(周五)下午15:30

  报告地点:紫台办公大楼619会议室

欢迎大家参加!

地址:(210008)南京市北京西路2号 电话:86-25-83332000 传真:86-25-83332091 Email:pmoo@pmo.ac.cn
版权所有:中国科学院紫金山天文台    http://www.pmo.cas.cn    备案序号:苏ICP备05007736号