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High-latitude intermediate-velocity clouds (IVCs) are part of the Milky Way's HI halo and originate from either a galactic fountain process or extragalactic gas infall. They are partly molecular and can most of the time be identified in CO.…

星系天体物理 · 物理学 2024-04-25 N. Schneider , V. Ossenkopf-Okada , E. Keilmann , M. Roellig , S. Kabanovic , L. Bonne , T. Csengeri , B. Klein , R. Simon , F. Comeron

We present HST GHRS and STIS observations of five QSOs that probe the prominent high-velocity cloud (HVC) Complex C, covering 10% of the northern sky. Based upon a single sightline measurement (Mrk 290), a metallicity [S/H]=-1.05+/-0.12 has…

Aims. We aim to investigate the ionisation conditions and distances of Galactic high-velocity clouds (HVCs) in the Galactic halo and beyond in the direction of the Local Group (LG) barycentre and anti-barycentre, by studying spectral data…

星系天体物理 · 物理学 2019-06-26 Sietske J. D. Bouma , Philipp Richter , Cora Fechner

We present an imaging survey aimed at searching for the stellar counterparts of recently discovered ultra-compact high-velocity HI clouds (UCHVC). Adams et al. (2013) proposed these clouds to be candidate mini-haloes in the Local Group…

星系天体物理 · 物理学 2015-06-23 M. Bellazzini , G. Beccari , G. Battaglia , N. Martin , V. Testa , R. Ibata , M. Correnti , F. Cusano , E. Sani

Observations with the Green Bank Telescope of 21cm HI emission from the high-velocity cloud Complex H suggest that it is interacting with the Milky Way. A model in which the cloud is a satellite of the Galaxy in an inclined, retrograde…

天体物理学 · 物理学 2009-11-07 Felix J. Lockman

Utilizing astrometric parameters sourced from \textit{Gaia} Data Release 3 and radial velocities obtained from various spectroscopic surveys, we identify 519 high-velocity stars (HiVels) with a total velocity in the Galactocentric restframe…

星系天体物理 · 物理学 2024-01-05 Jiwei Liao , Cuihua Du , Mingji Deng , Dashuang Ye , Hefan Li , Yang Huang , Jianrong Shi , Jun Ma

The high-velocity cloud (HVC) Complex A is a probe of the physical conditions in the Galactic halo. The kinematics, morphology, distance, and metallicity of Complex A indicate that it represents new material that is accreting onto the…

We present high resolution (R ~ 4 km/s) absorption measurements of the interstellar NaI and CaII lines measured towards 14 early-type stars of distance 123 pc - 1650 pc, located in the direction of the Ara OB1 stellar cluster. The line…

天体物理学 · 物理学 2009-06-23 Christopher D. Henderson , Barry Y. Welsh , John B. Hearnshaw

We present a study of the ionization and thermal structure of neutral hydrogen clouds located in the Galactic halo, immersed in the extragalactic background radiation field, and supposed to be in pressure equilibrium with the surrounding…

天体物理学 · 物理学 2009-10-22 Andrea Ferrara , George B. Field

We present a detailed analysis of the distance determination for one intermediate Velocity Cloud (IVC G139.6+47.6) from the ongoing DDO IVC Distance Project. Stars along the line of sight to G139.6+47.6 are examined for the presence of…

The mass assembly history of the Milky Way can inform both theory of galaxy formation and the underlying cosmological model. Thus, observational constraints on the properties of both its baryonic and dark matter contents are sought. Here we…

星系天体物理 · 物理学 2017-01-24 Elena M. Rossi , T. Marchetti , M. Cacciato , M. Kuiack , R. Sari

Optical emission lines have now been detected from about 20 high velocity clouds. These emission lines -- primarily H-alpha, secondarily [N II] and [S II] -- are very faint and diffuse, spread over the surfaces of the clouds. We compile…

天体物理学 · 物理学 2007-05-23 Benjamin J. Weiner , Stuart N. Vogel , T. B. Williams

We present the serendipitous discovery of the fastest Main Sequence hyper-velocity star (HVS) by the Southern Stellar Stream Spectroscopic Survey (S5). The star S5-HVS1 is a $\sim 2.35$ M$_\odot$ A-type star located at a distance of $\sim…

Intermediate and high velocity HI clouds rain onto the plane of our Galaxy. They are observed at heights of between 500 and 1500 pc, falling onto the Galactic plane at velocities from 50 to 140 km s$^{-1}$. To explain the origin of these…

星系天体物理 · 物理学 2015-05-13 A. Rodriguez-Gonzalez , A. C. Raga , J. Canto

Hypervelocity stars (HVSs) represent a unique class of objects capable of escaping the gravitational pull of the Milky Way due to extreme acceleration events, such as close encounters with the supermassive black hole at the Galactic center…

星系天体物理 · 物理学 2025-04-22 Yongkang Sun , Yang Huang , Jifeng Liu , Haozhu Fu , Huawei Zhang , Yinbi Li , Cuihua Du , Jianrong Shi , Xiao Kong

The Smith Cloud is a gaseous high-velocity cloud (HVC) in an advanced state of accretion, only 2.9 kpc below the Galactic plane and due to impact the disk in 27 Myr. It is unique among HVCs in having a known distance (12.4+/-1.3 kpc) and a…

We describe an ultraviolet spectroscopic survey of interstellar high-velocity cloud (HVC) absorption in the strong 1206.500 Angstrom line of Si III using the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope. Because…

星系天体物理 · 物理学 2015-05-14 Joseph A. Collins , Michael Shull , Mark L. Giroux

We present Westerbork Synthesis Radio Telescope HI images, Lovell Telescope multibeam HI wide-field mapping, Wisconsin H-alpha Mapper facility images, William Herschel Telescope longslit echelle CaII observations, and IRAS ISSA 60 and 100…

天体物理学 · 物理学 2009-11-07 J. V. Smoker , L. M. Haffner , F. P. Keenan , R. D. Davies , D. Pollacco

The Galactic Center regions $-6^\circ \le l \le 6^\circ$ and $-0.8^\circ \le b \le 0.87^\circ$ are surveyed with HCN J=1$-$0 line (88.6 GHz) on a 4$'$ grid with the 14 m telescope at the Taeduk Radio Astronomy Observatory. The data…

天体物理学 · 物理学 2009-10-28 Chang Won Lee

Searching the HI Parkes All-Sky Survey (HIPASS) and its northern extension, we detected a population of very compact high-velocity clouds (HVCs) with similar velocities in the Galactic standard-of-rest frame which appear to be arranged in…

天体物理学 · 物理学 2009-11-13 T. Westmeier , B. S. Koribalski