The High-Velocity Clouds: Galactic or Extragalactic?
نویسندگان
چکیده
منابع مشابه
Compact High Velocity Clouds
We summarize the observed properties of the CHVC population, which provide strong evidence for source distances in the range 200– 1000 kpc. At these distances, the population corresponds to strongly dark-matter dominated sub-dwarf galaxies still accreting onto the more massive Local Group systems. Recent searches for faint associated stellar populations have revealed red-giant candidates for wh...
متن کاملHighly Ionized High Velocity Clouds: Intergalactic Gas in the Local Group or Distant Gas in the Galactic Halo?
In the course of our studies of the gaseous halo surrounding the Milky Way, we have recently identified several high velocity (VLSR < -100 km s ) clouds in the directions of Mrk 509 and PKS 2155-304 that have unusual ionization properties. The clouds exhibit strong C IV absorption with little or no detectable low ion (C II, Si II) absorption or H I 21 cm emission down to very sensitive levels. ...
متن کاملLate Gas Accretion onto Primordial Minihalos: a Model for Leo T and Extragalactic High-velocity Clouds
In this letter we show that primordial minihalos with vcir < 20 km s −1 stop accreting gas after reionization, as is usually assumed, but in virtue of their increasing concentration and the decreasing temperature of the intergalactic medium as redshift decreases, they have a recent phase of gas accretion and possibly star formation. We expect that some pre-reionization fossils that evolved on t...
متن کاملOptical Emission from High Velocity Clouds and the Ionization Sources in the Galactic Halo
Optical emission lines have now been detected from about 20 high velocity clouds. These emission lines – primarily Hα, secondarily [N ii] and [S ii] – are very faint and diffuse, spread over the surfaces of the clouds. We compile emission line measurements and present a model in which the Hα is recombination caused by photoionizing radiation escaping the Milky Way. In such a model, we infer HVC...
متن کاملThe high-velocity clouds and the Magellanic Clouds
From an analysis of the sky and velocity distributions of the high-velocity clouds (HVCs) we show that the majority of the HVCs has a common origin. We conclude that the HVCs surround the Galaxy, forming a metacloud of ∼ 300 kpc in size and with a mass of ∼ 3×109 M⊙, and that they are the product of a powerful “superwind” (about 10 58 ergs), which occurred in the Magellanic Clouds about 570 Myr...
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ژورنال
عنوان ژورنال: International Astronomical Union Colloquium
سال: 1997
ISSN: 0252-9211
DOI: 10.1017/s025292110007144x