Cosmic Ray Heating Research Articles

Warming rays in cluster cool cores

Context. Cosmic rays are confined in the atmospheres of galaxy clusters and, therefore, they can play a crucial role in the heating of their cool cores. Aims. We discuss here the thermal and non-thermal features of a model of cosmic ray heating of cluster cores that can provide a solution to the cooling-flow problems. To this aim, we generalize a model originally proposed by Colafrancesco, Dar & DeRujula (2004) and we show that our model predicts specific correlations between the thermal and non-thermal properties of galaxy clusters and enables various observational tests. Methods. The model reproduces the observed temperature distribution in clusters by using an energy balance condition in which the X-ray energy emitted by clusters is supplied, in a quasi-steady state, by the hadronic cosmic rays, which act as “warming rays” (WRs). The temperature profile of the intracluster (IC) gas is strictly correlated with the pressure distribution of the WRs and, consequently, with the non-thermal emission (radio, hard X-ray and gamma-ray) induced by the interaction of the WRs with the IC gas and the IC magnetic field. Results. The temperature distribution of the IC gas in both cool-core and non cool-core clusters is successfully predicted from the measured IC plasma density distribution. Under this contraint, the WR model is also able to reproduce the thermal and non-thermal pressure distribution in clusters, as well as their radial entropy distribution, as shown by the analysis of three clusters studied in detail: Perseus, A2199 and Hydra. The WR model provides other observable features of galaxy clusters: a correlation of the pressure ratio (WRs to thermal IC gas) with the inner cluster temperature $(P_{\rm WR}/P_{\rm th}) \sim (kT_{\rm inner})^{-2/3}$, a correlation of the gamma-ray luminosity with the inner cluster temperature $L_{\gamma} \sim (kT_{\rm inner})^{4/3}$, a substantial number of cool-core clusters observable with the GLAST-LAT experiment, a surface brightness of radio halos in cool-core clusters that recovers the observed one, a hard X-ray ICS emission from cool-core clusters that is systematically lower than the observed limits and yet observable with the next generation high-sensitivity and spatial resolution HXR experiments like Simbol-X. Conclusions. The specific theoretical properties and the multi-frequency distribution of the e.m. signals predicted in the WR model render it quite different from the other models so far proposed for the heating of clusters' cool-cores. Such differences make it possible to prove or disprove our model as an explanation for the cooling-flow problems on the basis of multi-frequency observations of galaxy clusters.

Feedback heating by cosmic rays in clusters of galaxies

Recent observations show that the cooling flows in the central regions of galaxy clusters are highly suppressed. Observed active galactic nuclei (AGN)-induced cavities/bubbles are a leading candidate for suppressing cooling, usually via some form of mechanical heating. At the same time, observed X-ray cavities and synchrotron emission point towards a significant nonthermal particle population. Previous studies have focused on the dynamical effects of cosmic ray pressure support, but none has built successful models in which cosmic ray heating is significant. Here, we investigate a new model of AGN heating, in which the intracluster medium is efficiently heated by cosmic rays, which are injected into the intra-cluster medium (ICM) through diffusion or the shredding of the bubbles by Rayleigh‐Taylor or Kelvin‐Helmholtz instabilities. We include thermal conduction as well. Using numerical simulations, we show that the cooling catastrophe is efficiently suppressed. The cluster quickly relaxes to a quasiequilibrium state with a highly reduced accretion rate and temperature and density profiles which match observations. Unlike the conduction-only case, no fine-tuning of the Spitzer conduction suppression factor f is needed. The cosmic ray pressure, Pc/Pg � 0.1 and ∇Pc � 0.1ρg, is well within observational bounds. Cosmic ray heating is a very attractive alternative to mechanical heating, and may become particularly compelling if Gamma-ray Large Array Space Telescope (GLAST) detects the γ -ray signature of cosmic rays in clusters.

Desorption from interstellar ices

The desorption of molecular species from ice mantles back into the gas phase in molecular clouds results from a variety of very poorly understood processes. We have investigated three mechanisms: desorption resulting from H2 formation on grains, direct cosmic ray heating and cosmic ray-induced photodesorption. Whilst qualitative differences exist between these processes (essentially deriving from the assumptions concerning the species selectivity of the desorption and the assumed threshold adsorption energies, Et), all the three processes are found to be potentially very significant in dark cloud conditions. It is therefore important that all three mechanisms should be considered in studies of molecular clouds in which freeze-out and desorption are believed to be important. Employing a chemical model of a typical static molecular core and using likely estimates for the quantum yields of the three processes, we find that desorption by H2 formation probably dominates over the other two mechanisms. However, the physics of the desorption processes and the nature of the dust grains and ice mantles are very poorly constrained. We therefore conclude that the best approach is to set empirical constraints on the desorption, based on observed molecular depletions – rather than try to establish the desorption efficiencies from purely theoretical considerations. Applying this method to one such object (L16 89B) yields upper limits to the desorption efficiencies that are consistent with our understanding of these mechanisms.

Cosmic-Ray Heating of Molecular Gas in the Nuclear Disk: Low Star Formation Efficiency

Understanding the processes occurring in the nuclear disk of our Galaxy is interesting in its own right, as part of the Milky Way, but also because it is the closest galactic nucleus. It has been more than two decades since the general phenomenon of higher gas temperature in the inner few hundred parsecs by comparison with local clouds in the disk of the Galaxy was recognized. This is one of the least understood characteristics of giant molecular clouds having a much higher gas temperature than dust temperature in the inner few degrees of the Galactic center. We propose that an enhanced flux of cosmic-ray electrons, as evidenced recently by a number of studies, is responsible for directly heating the gas clouds in the nuclear disk, elevating the temperature of molecular gas (~75 K) above the dust temperature (~20 K). In addition, we report the detection of nonthermal radio emission from Sgr B2 F based on low-frequency GMRT and VLA observations. The higher ionization fraction and thermal energy due to the impact of nonthermal electrons in star-forming sites have important implications in slowing down star formation in the nuclear disk of our Galaxy and nuclei of galaxies.

The Origin of Diffuse X‐Ray and γ‐Ray Emission from the Galactic Center Region: Cosmic‐Ray Particles

The inner couple of hundred parsecs of our Galaxy are characterized by a significant amount of synchrotron-emitting gas. Many of best studied sources in this region exhibit a mixture of 6.4 keV Fe Kα emission, molecular line emission, and nonthermal radio continuum radiation. The spatial correlation between fluorescent Fe Kα line emission at 6.4 keV and molecular line emission from Galactic center molecular clouds has been explained as reflected X-rays from a past outburst of Sgr A*. Here we present a multiwavelength study of this region and find a correlation between nonthermal radio filaments and X-ray features. This correlation, when combined with distribution of molecular gas, suggests against irradiation model. Instead, we account for this distribution in terms of impact of relativistic particles from local (nonthermal filaments) and extended sources with diffuse neutral gas producing both nonthermal bremsstrahlung X-ray continuum emission and diffuse 6.4 keV line emission. The production rate of Fe Kα photons associated with injection of electrons into a cloud as a function of column density is calculated. The required energy density of low-energy cosmic rays associated with synchrotron-emitting radio filaments or extended features is estimated to be in range between 20 and ~103 eV cm-3 for Sgr C, Sgr B1, Sgr B2, and the 45 and -30 km s-1 clouds. We also generalize this idea to explain cosmic-ray heating of molecular gas, interstellar cosmic-ray ionization, pervasive production of diffuse Kα line, and TeV emission from Galactic center molecular clouds. In particular, we suggest that inverse Compton scattering of submillimeter radiation from dust by relativistic electrons may contribute substantially to large-scale diffuse TeV emission observed toward central regions of Galaxy.

The Chemistry of Multiply Deuterated Molecules in Protoplanetary Disks. I. The Outer Disk

We present new models of the deuterium chemistry in protoplanetary disks, including, for the first time, multiply deuterated species. We use these models to explore whether observations in combination with models can give us clues as to which desorption processes occur in disks. We find, in common with other authors, that photodesorption can allow strongly bound molecules such as HDO to exist in the gas phase in a layer above the midplane. Models including this process give the best agreement with the observations. In the midplane, cosmic ray heating can desorb weakly bound molecules such as CO and N$_2$. We find the observations suggest that N$_2$ is gaseous in this region, but that CO must be retained on the grains to account for the observed DCO$^+$/HCO$^+$. This could be achieved by CO having a higher binding energy than N$_2$ (as may be the case when these molecules are accreted onto water ice) or by a smaller cosmic ray desorption rate for CO than assumed here, as suggested by recent theoretical work. For gaseous molecules the calculated deuteration can be greatly changed by chemical processing in the disk from the input molecular cloud values. On the grains singly deuterated species tend to retain the D/H ratio set in the molecular cloud, whereas multiply deuterated species are more affected by the disk chemistry. Consequently the D/H ratios observed in comets may be partly set in the parent cloud and partly in the disk, depending on the molecule.

Population III Generated Cosmic Rays and the Production of6Li

We calculate the evolution of 6 Li generated from cosmic rays produced by an early population of massive stars. The computation is performed in the framework of hierarchical structure formation and is based on cosmic star for- mation histories constrained to reproduce the observed star formation rate at redshift zP6 and the observed chemical abundances both in damped Lyabsorbers and in the intergalactic medium, and to allow for an early reionization of theuniverseatz � 11byPopulationIIIstarsasindicatedbythethirdyearresultsreleasedbyWMAP.Weshowthatthe pregalactic production of the 6 Li isotope in the IGM via these Population III stars can account for the 6 Li plateau observed in metal-poor halo stars without additional overproduction of 7 Li. Our results depend on the efficiency of cosmic rays to propagate out of minihalos and the fraction of supernova energy deposited in cosmic rays. We also compute the cosmic-ray heating of the IGM gas. In general, we find somewhat high temperatures (of order 10 5 K), implying that the cosmic rays production of 6Li may be required to be confined to the so-called warm-hot IGM. Subject headingg cosmic rays — cosmology: theory — nuclear reactions, nucleosynthesis, abundances — stars: abundances

Modeling the dust and gas temperatures near young stars

AbstractAs young stars form, they interact with their environment in many ways. We study the radiative interaction of a young star with its surrounding cluster environment. The change in gas temperature caused by a forming star can trigger the formation or inhibit the growth of nearby star forming cores. We calculate the gas temperature around a single star by balancing the dust-gas collisional heating, molecular cooling, and cosmic ray heating rates for a grid of models with various luminosities and density distributions. In the future, this work can be used in large-scale simulations of clustered star formation to study the effect of using a gas temperature which depends not only on density, but also on radiative environment.

The effect of non-isothermality on the gravitational collapse of spherical clouds and the evolution of protostellar accretion

We investigate the role of non-isothermality in gravitational collapse and protostellar accretion by explicitly including the effects of molecular radiative cooling, gas-dust energy transfer, and cosmic ray heating in models of spherical hydrodynamic collapse. Isothermal models have previously shown an initial decline in the mass accretion rate \dot{M}, due to a gradient of infall speed that develops in the prestellar phase. Our results show that: (1) in the idealized limit of optically thin cooling, a positive temperature gradient is present in the prestellar phase which effectively cancels out the effect of the velocity gradient, producing a near constant \dot{M} in the early accretion phase; (2) in the more realistic case including cooling saturation at higher densities, \dot{M} may initially be either weakly increasing or weakly decreasing with time, for low (T_d ~ 6 K) and high dust temperature (T_d ~ 10 K) cases, respectively. Hence, our results show that the initial decline in \dot{M} seen in isothermal models is definitely not enhanced by non-isothermal effects, and is often suppressed by them. In all our models, \dot{M} does eventually decline rapidly due to the finite mass condition on our cores and a resulting inward propagating rarefaction wave. Thus, any explanation for a rapid decline of $\dot{M}$ in the accretion phase likely needs to appeal to the global molecular cloud structure and possible envelope support, which results in a finite mass reservoir for cores.

Confinement-driven Spatial Variations in the Cosmic-Ray Flux

Low-energy cosmic rays (CRs) are confined by self-generated MHD waves in the mostly neutral interstellar medium. We show that the CR transport equation can be expressed as a continuity equation for the CR number density involving an effective convection velocity. Assuming a balance between wave growth and ion-neutral damping, this equation gives a steady state condition ncr ∝ n up to a critical density for free streaming. This relation naturally accounts for the heretofore unexplained difference in CR ionization rates derived for dense diffuse clouds (McCall et al.) and dark clouds, and predicts large spatial variations in the CR heating rate and pressure.

Monte Carlo radiative transfer in molecular cloud cores

We present the results of a three-dimensional Monte Carlo radiative transfer code for starless molecular cloud cores heated by an external isotropic or non-isotropic interstellar radiation field. The code computes the dust temperature distribution inside model clouds with specified but arbitrary density profiles. In particular we examine in detail spherical (Bonnor-Ebert) clouds, axisymmetric and non-axisymmetric toroids, and clouds heated by an external stellar source in addition to the general interstellar field. For these configurations, the code also computes maps of the emergent intensity at different wavelengths and arbitrary viewing angle, that can be compared directly with continuum maps of prestellar cores. In the approximation where the dust temperature is independent of interactions with the gas and where the gas is heated both by collisions with dust grains and ionization by cosmic rays, the temperature distribution of the gas is also calculated. For cloud models with parameters typical of dense cores, the results show that the dust temperature decreases monotonically from a maximum value near the cloud's edge (14-15 K) to a minimum value at the cloud's center (6-7 K). Conversely, the gas temperature varies in a similar range, but, due to efficient dust-gas coupling in the inner regions and inefficient cosmic-ray heating in the outer regions, the gradient is non-monotonic and the gas temperature reaches a maximum value at intermediate radii. The emission computed for these models (at 350 micron and 1.3 mm) shows that deviations from spherical symmetry in the density and/or temperature distributions are generally reduced in the simulated intensity maps (even without beam convolution), especially at the longer wavelengths.

Cosmic ray induced explosive chemical desorption in dense clouds

The desorption due to the energy release of free radicals in the ice mantles of a dust grain is investigated theoretically by calculating the ultraviolet radiation field inside the cloud, the free radical accumulation, the cosmic-ray heating of the grain and then the desorption in this situation starting from the cosmic-ray energy spectra. This model can reproduce the observations of the CO gas abundances and level of depletion in dark clouds such as L977 and IC 5146 with a combination of input parameters which are either constrained by independent observations or have been derived independently from laboratory experiments. We investigate other desorption mechanisms and conclude that they cannot explain the observations. The model also shows that the energy input by the cosmic-ray induced ultraviolet field is almost one order of magnitude larger than the direct energy input by cosmic-ray particles. This strengthens the conclusion that desorption due to the energy release by ultraviolet photon produced radicals dominates over direct cosmic-ray desorption.

CO (J = 7→6) Observations of NGC 253: Cosmic‐Ray–heated Warm Molecular Gas

We report observations of the CO J = 7 → 6 transition toward the starburst nucleus of NGC 253. This is the highest excitation CO measurement in this source to date and allows an estimate of the molecular gas excitation conditions. Comparison of the CO line intensities with a large velocity gradient, escape probability model indicates that the bulk of the × 107 M☉ of molecular gas in the central 180 pc is highly excited. A model with T ~ 120 K, n ~ 4.5 × 104 cm-3, is consistent with the observed CO intensities, as well as the rotational H2 lines observed with the Infrared Space Observatory. The inferred mass of warm, dense molecular gas is 10-30 times the atomic gas mass as traced through its [C II] and [O I] line emission. This large mass ratio is inconsistent with photodissociation region models in which the gas is heated by far-UV starlight. It is also not likely that the gas is heated by shocks in outflows or cloud-cloud collisions. We conclude that the best mechanism for heating the gas is cosmic rays, which provide a natural means of uniformly heating the full volume of molecular clouds. With the tremendous supernova rate in the nucleus of NGC 253, the cosmic-ray heating rate is at least ~800 times greater than that in the Galaxy, more than sufficient to match the cooling observed in the CO lines.

The structure and stability of molecular cloud cores in external radiation fields

We have considered the thermal equilibrium in pre-protostellar cores in the approximation where the dust tempera- ture is independent of interactions with the gas and where the gas is heated both by collisions with dust grains and ionization by cosmic rays. We have then used these results to study the stability of cores in hydrostatic equilibrium in the limit where thermal pressure dominates over magnetic field and turbulence. We compare the density distribution derived in this manner with results obtained in the isothermal case. We find that for cores with characteristics similar to those observed in nearby molecular clouds, the gas and dust temperatures are coupled in the core interior with densities above ∼3×10 4 cm −3 . As a consequence, one expects that the gas temperature like the dust temperature decreases towards the center of these objects. However, the regime where gas and dust temperatures are coupled coincides approximately with that in which CO and many other molecular species deplete onto dust grain surfaces. At larger radii and lower densities, the gas and dust temperatures decouple and the gas temperature tends to the value expected for cosmic ray heating alone. The density structure which one computes taking into account such deviations from isothermality are not greatly different from that expected for an isothermal Bonnor-Ebert sphere. It is impossi- ble in the framework of these models to have a stable equilibrium core with mass above ∼5 Mand column density compatible with observed values (NH > 2 × 10 22 cm −2 or AV > 10 mag). We conclude from this that observed high mass cores are either supported by magnetic field or turbulence or are already in a state of collapse. Lower mass cores on the other hand have stable states where thermal pressure alone provides support against gravitation and we conclude that the much studied object B68 may be in a state of stable equilibrium if the internal gas temperature is computed in self-consistent fashion. Finally we note that in molecular clouds such as Ophiuchus and Orion with high radiation fields and pressures, gas and dust temperatures are expected to be well coupled and hence in the absence of an internal heat source, one expects temperatures to decrease towards core centers and to be relatively high as compared to low pressure clouds like Taurus.

Chemistry in grain aggregates: a source of complex molecules?

ABSTRA C T The aggregation of grains in dense protostellar clouds brings together materials such as silicates, carbons, polycyclic aromatic hydrocarbons and ices to form porous structures with high internal volume. Some physical and chemical properties of these aggregate grains are discussed in the context of the role that they may play in the formation of complex organic and organometallic compounds. One characteristic of such grains that is unique outside planetary systems is the availability of all elements and a number of their common compounds in a composite solid. In dark clouds, the chemistry inside aggregate grains will be driven by cosmic ray heating and sputtering. This occurs in an environment where the products of such reactions can be retained within the dust particle. Hot atom chemistry and secondary reactions are facilitated by the re-entrant nature of such aggregated structures, leading to the possible formation of complex organic compounds. In particular, the sputtering of Si, Mg and Fe from silicate dust is discussed, and it is shown that a variety of organometallic compounds could be expected in ices within aggregate grains. The optical depth for ultraviolet light within aggregates is large, so that materials inside such grains will be effectively shielded from ambient radiation. However, the incorporation of luminifors such as those grain components responsible for the extended red emission converts ultraviolet to visible and near-infrared radiation, and might moderate photochemistry within aggregates. It is suggested that the chemical environment within aggregates may be conducive to the formation and retention of complex molecules such as amino acids, peptides and a variety of organometallic compounds.

Ambipolar Drift Heating in Turbulent Molecular Clouds

Although thermal pressure is unimportant dynamically in most molecular gas, the temperature is an important diagnostic of dynamical processes and physical conditions. This is the first of two papers on thermal equilibrium in molecular clouds. We present calculations of frictional heating by ion-neutral (or ambipolar) drift in three-dimensional simulations of turbulent, magnetized molecular clouds. We show that ambipolar drift heating is a strong function of position in a turbulent cloud, and its average value can be significantly larger than the average cosmic ray heating rate. The volume averaged heating rate per unit volume due to ambipolar drift, H_AD ~ |JxB|^2 ~ B^4/L_B^2, is found to depend on the rms Alfvenic Mach number, M_A, and on the average field strength, as H_AD ~ M_A^2 ^4. This implies that the typical scale of variation of the magnetic field, L_B, is inversely proportional to M_A, which we also demonstrate.

Thermal Stability of Cold Clouds in Galaxy Halos

We consider the thermal properties of cold, dense clouds of molecular hydrogen and atomic helium. For cloud masses below 10-1.7 M middle dot in circle, the internal pressure is sufficient to permit the existence of particles of solid or liquid hydrogen at temperatures above the cosmic microwave background temperature. Optically thin thermal continuum emission by these particles can balance cosmic-ray heating of the cloud, leading to equilibria that are thermally stable even though the heating rate is independent of cloud temperature. For the Galaxy, the known heating rate in the disk sets a minimum mass of order 10-6 M middle dot in circle necessary for survival. Clouds of this type may in principle comprise most of the dark matter in the Galactic halo. However, we caution that the equilibria do not exist at redshifts z greater, similar1 when the temperature of the microwave background was substantially larger than its current value; therefore, the formation and the survival of such clouds to the present epoch remain open questions.

High resolution thermometry for the confined helium experiment

We report results with a newly designedCu(NH 4 ) 2 Br 4 ·2H 2 O paramagnetic salt high resolution thermometry that will be used in the confined helium experiment to be flown on space Shuttle. The improved thermometry has a fast response time and can measure temperature with a resolution of 0.3 nK in a 10 Hz bandwidth. Our measurements have shown that the effect of cosmic ray heating observed in the lambda point experiment in space can be reduced to a negligible level. The current thermometry appears capable of operating in space at the limit imposed by thermodynamic fluctuations.

The Distribution of the Dense Clouds in the Starburst Nucleus of NGC 253

We present 2'' ? 4'' resolution aperture synthesis observations of HCN J = 1 ? 0 emission from the starburst galaxy NGC 253. Because of its large critical density, HCN traces dense (nH2 104 cm-3) molecular gas. The emission lies along a central bar in several unresolved (r 30 pc) complexes. At 7'' resolution the HCN J = 1 ? 0/CO J = 1 ? 0 intensity ratio, a measure of density, has a maximum value of 0.2. Excitation models suggest that the HCN-emitting clouds in NGC 253 have high temperatures (100 K), densities (nH2 ~ 104-105 cm-3), and beam-averaged column densities (NH2 ~ 3-10 ? 1022 cm-2). We find a rough association between the star-forming regions in NGC 253 (radio continuum emission) and the molecular cloud complexes. Most of the radio sources have been interpreted as supernova remnants, but several have flat spectral indices typical of thermal emission from H II regions. The radio continuum sources have up to 100 times the radio luminosity of W49, the most luminous H II region complex in the Milky Way. The high cloud temperatures we infer for NGC 253 are most likely due to intense ultraviolet radiation from massive star formation and enhanced cosmic-ray heating by supernovae. The HCN distributions in NGC 253 and the Galactic center are remarkably similar when compared on the same spatial scale. They are asymmetric with longitude, and the peaks lie 100-200 pc away from the nucleus. However, the HCN luminosity and HCN/CO intensity ratio are several times higher in NGC 253 than in the Milky Way. Therefore, the average gas densities and the mass of dense gas are larger in the starburst nucleus of NGC 253.

The cold, massive molecular cloud G216-2.5. 2: Structure and kinematics

view Abstract Citations (28) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Cold, Massive Molecular Cloud G216-2.5. II. Structure and Kinematics Lee, Youngung ; Snell, Ronald L. ; Dickman, Robert L. Abstract We have studied the gas properties and kinematics of G216-2.5 (also called Maddalena's cloud), a cold, massive giant molecular cloud (GMC) with no obvious signs of star formation. We have mapped 11 square degrees of the cloud in the J = 1 goes to 0 transitions of (12)CO and (13)CO using the QUARRY 15 beam array receiver on the 14 m telescope at Five College Radio Astronomy Observatory (FCRAO). We confirm the results of Maddalena & Thaddeus (1985) that the cloud is unusually cold and has very broad line widths (Delta V approximately 8 km/s). The exceptionally low gas temperatures (less than 8 K) can be explained if the cosmic-ray heating rate is reduced by a factor of 2 in the outer Galaxy. The mass of the cloud has been established by several techniques, and masses between 1 x 105 and 6 x 105 solar mass were obtained. We suggest that G216-2.5 is a remnant cloud from a past episode of massive star formation, for the following reasons. First, the cloud has a relatively large velocity dispersion for a non-star-forming GMC. Second, there is a clear evidence for shells and rings within the cloud, which may be the fossil remains of its earlier star formation activity. Third, the kinematics of the cloud are dominated by a global velocity gradient, suggesting that the cloud is part of a very large expanding shell. Finally, the discrepancy between the local thermodynamic equilibrium (LTE) and virial masses may be explained if the cloud has been severely perturbed and is currently expanding. G216-2.5 may be part of a larger star-forming complex that includes the adjacent H II region S287 and its molecular cloud. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174558 Bibcode: 1994ApJ...432..167L Keywords: Carbon Monoxide; Dynamic Characteristics; Emission Spectra; Interstellar Matter; Kinematics; Line Spectra; Molecular Clouds; Radio Astronomy; Radio Spectra; Extremely High Frequencies; Local Thermodynamic Equilibrium; Mass; Millimeter Waves; Star Formation; Velocity Distribution; Astronomy; ISM: KINEMATICS AND DYNAMICS; ISM: INDIVIDUAL ALPHANUMERIC: G216-2.5; ISM: MOLECULES; RADIO LINES: ISM full text sources ADS | data products SIMBAD (7) Related Materials (2) Part 1: 1992PhDT.........7L Part 3: 1996ApJ...472..275L