Cloud Disruption Research Articles

The Magellanic Stream and other hydrogen remnants of strong tidal disruption of the Magellanic Clouds

view Abstract Citations (32) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Magellanic Stream and other hydrogen remnants of strong tidal disruption of the Magellanic Clouds Mirabel, I. F. Abstract A review of results from recent surveys of neutral-hydrogen, high-velocity clouds reveals the connection of the Magellanic Stream with a widespread population of clouds with large infalling motions toward the Galaxy. The tidal disruption of the Magellanic Clouds during their last close encounter with the Milky Way produced, along with the Magellanic Stream, a population of high-velocity clouds scattered throughout the first and second quadrants of the southern galactic hemisphere. High angular resolution observations in the northern tip of the Magellanic Stream are presented. They show that the leading head of the Stream is disintegrating as it falls toward the Milky Way. The scattering material may be observed as a conglomerate of discrete clouds surrounding the tip of the Magellanic Stream. The need for new computer simulations of the remnants of strong tidal disruption of the Magellanic Clouds is discussed. Publication: The Astrophysical Journal Pub Date: November 1981 DOI: 10.1086/159399 Bibcode: 1981ApJ...250..528M Keywords: Hydrogen Clouds; Magellanic Clouds; Neutral Gases; Radio Sources (Astronomy); Tides; Centimeter Waves; Computerized Simulation; Gas Density; Milky Way Galaxy; Astrophysics full text sources ADS |

The Disruption of the Molecular Cloud Associated with the North America and Pelican Nebulae

Giant molecular clouds can be destroyed in several ways: by conversion of gas into stars; by dissociation of H2 into HI; by ionization and formation of HII regions; and by dispersal of the cloud into cloudets. The relative importance of these processes can be assessed by observations of evolved HII regions and associated molecular clouds. A number of such complexes have been studied in 12CO at the Five College Radio Astronomy Observatory (FCRAO) as part of an extensive investigation of clouds associated with about 60 Sharpless HII regions. A particularly clear example of cloud disruption is found in the case of W80, the North America and Pelican Nebulae in Cygnus (Bally and Scoville 1980).

Long chain carbon molecules and diffuse interstellar lines

THE diffuse interstellar lines, seen in the optical spectra of stars which lie behind fairly low density interstellar clouds, have remained unidentified for many years. It has recently been suggested1 that the diffuse interstellar lines are the absorption bands of long chain carbon molecules, Cn, where n may be in the range 5–15. As one possible source for these molecules, Douglas1 proposes that long chain hydrocarbons are synthesised in dense interstellar clouds. After cloud disruption, the hydrocarbons may lose their hydrogen atoms by photodissociation and exist as pure carbon chains. While the shortest of the chains (C2, C3, C4) will themselves be photodissociated, Douglas1 argues that chains beyond a certain length are stable against photodissociation and will persist in the low density clouds in which the diffuse interstellar lines are formed. As a first step in evaluating the feasibility of this route, we estimate here the abundances of chain hydrocarbon molecules which would be expected in dense interstellar clouds as a result of gas-phase chemistry alone. The rather high abundances of hydrocarbons which we predict support the identification of carbon chains as the source of the diffuse interstellar spectral features.

Non-linear primordial fluctuations

Matter in the early Universe (103 < z < 1012) could have been extremely inhomogeneous. Photon diffusion and neutrino diffusion alter the density contrast of matter, which can lead to collapse or disruption of primordial clouds. Nucleosynthesis proceeds differently in dense regions, so observed abundances provide a clue to the lumpiness at T ∼ 109 K. Clouds which eventually collapse can form stars, but not one of the visible populations, because no choice of parameters yields correct C, N and O abundances. Neutrino diffusion effects limit the range of possible nuclear abundances in clouds which disperse and mix with visible matter: gas cannot emerge from the big bang with a higher metal content than metal-poor halo stars. A wide range of conditions at recombination is consistent with available evidence.

The Mass Spectrum of Interstellar Clouds and the Assumption of Total Coalescence

We have investigated some modifications of the statistical mechanical model for the formation and disruption of interstellar clouds originally proposed by Field and Saslaw. We conclude that the asymptotic nature of the mass spectrum (i.e. N ( m ) ≈ m−3/2 ), under the assumptions of total coalescence and uniform σv , is independent of the redistribution of the larger clouds into the smaller ones and the time dependence of the problem. We also describe some preliminary results of more detailed model calculations.