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A population of dust-enshrouded objects orbiting the Galactic black hole 期刊论文
NATURE, 2020, 577 (7790) : 337-+
作者:  Witze, Alexandra
收藏  |  浏览/下载:26/0  |  提交时间:2020/07/03

The central 0.1 parsecs of the Milky Way host a supermassive black hole identified with the position of the radio and infrared source Sagittarius A* (refs.(1,2)), a cluster of young, massive stars (the S stars3) and various gaseous features(4,5). Recently, two unusual objects have been found to be closely orbiting Sagittarius A*: the so-called G sources, G1 and G2. These objects are unresolved (having a size of the order of 100 astronomical units, except at periapse, where the tidal interaction with the black hole stretches them along the orbit) and they show both thermal dust emission and line emission from ionized gas(6-10). G1 and G2 have generated attention because they appear to be tidally interacting with the supermassive Galactic black hole, possibly enhancing its accretion activity. No broad consensus has yet been reached concerning their nature: the G objects show the characteristics of gas and dust clouds but display the dynamical properties of stellar-mass objects. Here we report observations of four additional G objects, all lying within 0.04 parsecs of the black hole and forming a class that is probably unique to this environment. The widely varying orbits derived for the six G objects demonstrate that they were commonly but separately formed.


  
Spectroscopic confirmation of a mature galaxy cluster at a redshift of 2 期刊论文
NATURE, 2020, 577 (7788) : 39-+
作者:  Willis, J. P.;  Canning, R. E. A.;  Noordeh, E. S.;  Allen, S. W.;  King, A. L.;  Mantz, A.;  Morris, R. G.;  Stanford, S. A.;  Brammer, G.
收藏  |  浏览/下载:36/0  |  提交时间:2020/07/03

Galaxy clusters are the most massive virialized structures in the Universe and are formed through the gravitational accretion of matter over cosmic time(1). The discovery(2) of an evolved galaxy cluster at redshift z = 2, corresponding to a look-back time of 10.4 billion years, provides an opportunity to study its properties. The galaxy cluster XLSSC 122 was originally detected as a faint, extended X-ray source in the XMM Large Scale Structure survey and was revealed to be coincident with a compact over-density of galaxies(2) with photometric redshifts of 1.9 +/- 0.2. Subsequent observations3 at millimetre wavelengths detected a Sunyaev-Zel'  dovich decrement along the line of sight to XLSSC 122, thus confirming the existence of hot intracluster gas, while deep imaging spectroscopy from the European Space Agency'  s X-ray Multi-Mirror Mission (XMM-Newton) revealed(4) an extended, X-ray-bright gaseous atmosphere with a virial temperature of 60 million Kelvin, enriched with metals to the same extent as are local clusters. Here we report optical spectroscopic observations of XLSSC 122 and identify 37 member galaxies at a mean redshift of 1.98, corresponding to a look-back time of 10.4 billion years. We use photometry to determine a mean, dust-free stellar age of 2.98 billion years, indicating that star formation commenced in these galaxies at a mean redshift of 12, when the Universe was only 370 million years old. The full range of inferred formation redshifts, including the effects of dust, covers the interval from 7 to 13. These observations confirm that XLSSC 122 is a remarkably mature galaxy cluster with both evolved stellar populations in the member galaxies and a hot, metal-rich gas composing the intracluster medium.


  
Characteristics and sources of organic carbon in coastal and marine atmospheric particulates over East China 期刊论文
ATMOSPHERIC RESEARCH, 2019, 228: 281-291
作者:  Ding, Xue;  Qi, Jianhua;  Meng, Xiangbin
收藏  |  浏览/下载:19/0  |  提交时间:2019/11/27
Aerosols  Organic Carbon  WSOC  Dust  Source  
Identification and Characterization of Dust Source Regions Across North Africa and the Middle East Using MISR Satellite Observations 期刊论文
GEOPHYSICAL RESEARCH LETTERS, 2018, 45 (13) : 6690-6701
作者:  Yu, Yan;  Kalashnikova, Olga V.;  Garay, Michael J.;  Lee, Huikyo;  Notaro, Michael
收藏  |  浏览/下载:16/0  |  提交时间:2019/04/09
dust source  MISR  AOD  dust plume motion  
Stoichiometry of water-soluble ions in PM2.5: Application in source apportionment for a typical industrial city in semi-arid region, Northwest China 期刊论文
ATMOSPHERIC RESEARCH, 2018, 204: 149-160
作者:  Zhou, Haijun;  Lu, Changwei;  He, Jiang;  Gao, Manshu;  Zhao, Boyi;  Ren, Limin;  Zhang, Lijun;  Fan, Qingyun;  Liu, Tao;  He, Zhongxiang;  Dudagula;  Zhou, Bin;  Liu, Hualin;  Zhang, Yu
收藏  |  浏览/下载:10/0  |  提交时间:2019/04/09
Water-soluble ions  Stoichiometry  PM2.5  Source apportionment  Dust storm days  Haze days  
Disentangling the major source areas for an intense aerosol advection in the Central Mediterranean on the basis of Potential Source Contribution Function modeling of chemical and size distribution measurements 期刊论文
ATMOSPHERIC RESEARCH, 2018, 204: 67-77
作者:  Petroselli, Chiara;  Crocchianti, Stefano;  Moroni, Beatrice;  Castellini, Silvia;  Selvaggi, Roberta;  Nava, Silvia;  Calzolai, Giulia;  Lucarelli, Franco;  Cappelletti, David
收藏  |  浏览/下载:19/0  |  提交时间:2019/04/09
Potential Source Contribution Function  Aerosol size distribution  Biomass burning  Long-range transport  Saharan dust  
Effect of windblown dust from local and regional sources on the air quality of the central district in Jinan, China 期刊论文
ATMOSPHERIC RESEARCH, 2017, 185
作者:  Chen, Li;  Zhao, Hong;  Wang, Wenxing;  Bai, Zhipeng;  Wang, Zhongliang;  Sun, Fengjuan;  Hou, Lujian;  Liu, Guanghui;  Shi, Mengshuang;  Miao, Yunge
收藏  |  浏览/下载:14/0  |  提交时间:2019/04/09
Windblown dust  PM10  WEPS  CMAQ  Local source  Regional source