Cold Atomic Hydrogen Research Articles

Intergalactic Matter and Radiation and its Bearing on Galaxy Formation and Evolution

An up-dated review is given of the evidence for the presence of intergalactic matter and radiation in the Universe. It is concluded that the only important constituents which may make a sizable contribution to the total mass-energy are intergalactic gas and condensed objects with a very high mass-to-light ratio. If the QSOs are not at cosmological distances, cold atomic hydrogen may still be the most important constituent and may contribute much more mass than do the galaxies. The X-ray observations still do not unambiguously show that very hot gas is present, though it is very likely on general grounds that some hot gas is present in clusters of galaxies.The question of whether or not large amounts of matter, enough to close the Universe, are present, remains unsettled. From the theoretical standpoint the answer depends almost completely on the approach taken to the problem of galaxy formation and to the cosmological model which is favoured.

Observations of OH Molecules in Interstellar Dust Clouds

view Abstract Citations (47) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Observations of OH Molecules in Interstellar Dust Clouds Crutcher, Richard M. Abstract Sixty-two Lynds dust clouds have been searched in the 1 667-MHz line of OH; 74 percent were detected to an rms noise level of about 0.03 K. Those clouds already searched by Cudaback and Heiles were generally avoided. The survey concentrated on very opaque clouds, those assigned by Lynds to her opacity class 4, 5, or 6. The high detection rate strongly suggests that all very opaque dust clouds have significant OH densities. The OH velocity data are used to discuss the kinematics of the local dust-cloud population. A third of the 62 clouds were also searched for formaldehyde by Dieter. Most of these clouds have formaldehyde and OH lines at the same velocity. There is no correlation in the antenna temperatures of the two molecules. The molecular half-widths correlate strongly, but the formaldehyde half-widths are significantly smaller than those of the OH lines. In addition, several positions in the cold cloud seen in hydrogen self-absorption in the direction of the galactic center were searched for OH. It is shown that this cloud must contain both cold atomic hydrogen and OH molecules. Finally, the only known dust cloud with a large excess hydrogen brightness temperature has been found to have OH emission at about the same velocity as the atomic hydrogen. Subject headings: molecules, interstellar - nebulae Publication: The Astrophysical Journal Pub Date: November 1973 DOI: 10.1086/152460 Bibcode: 1973ApJ...185..857C full text sources ADS |