相关论文: Cosmic rays and the primordial gas
Cosmic structure originated from minute density perturbations in an almost homogeneous universe. The first stars are believed to be very massive and luminous, providing the first ionizing radiation and heavy elements to the universe and…
In massive primordial galaxies, the gas may directly collapse and form a single central massive object if cooling is suppressed. Line cooling by molecular hydrogen can be suppressed in the presence of a strong soft-ultraviolet radiation…
A field with particularly exciting results over the past few years is the study of the interaction of cosmic rays with interstellar matter. For star formation to take place, gas and dust need to be sufficiently cold for gravity to overcome…
We explore the implications of a possible cosmic ray (CR) background generated during the first supernova explosions that end the brief lives of massive Population III stars. We show that such a CR background could have significantly…
We investigate the formation of molecular hydrogen (H_2) in a primordial H+He gas cloud irradiated by a power-law UV flux. We find that at high densities (>1 cm^{-3}) and low temperatures (<10^4 K), the background radiation enhances the…
At low temperatures, the main coolant in primordial gas is molecular hydrogen, H2. Recent work has shown that primordial gas that is not collapsing gravitationally but is cooling from an initially ionized state forms hydrogen deuteride, HD,…
Understanding the processes occurring in the nuclear disk of our Galaxy is interesting in its own right, as part of the Milky Way Galaxy, but also because it is the closest galactic nucleus. It has been more than two decades since it was…
Cosmic rays may be linked to the formation of volatiles necessary for prebiotic chemistry. We explore the effect of cosmic rays in a hydrogen-dominated atmosphere, as a proof-of-concept that ion-neutral chemistry may be important for…
The first luminous objects in the concordance cosmology form by molecular hydrogen cooling in dark matter dominated halos of masses ~10^6 M_sun. We use Eulerian adaptive mesh refinement simulations to demonstrate that in the presence of a…
The first generation of protogalaxies likely formed out of primordial gas via H2-cooling in cosmological minihalos with virial temperatures of a few 1000K. However, their abundance is likely to have been severely limited by feedback…
The presence of small amounts of atomic hydrogen, detected as absorption dips in the 21 cm line spectrum, is a well-known characteristic of dark clouds. The abundance of hydrogen atoms measured in the densest regions of molecular clouds can…
Supernova explosions in the early star forming galaxies will accelerate cosmic rays (CRs). CRs are typically confined in the collapsed objects for a short period before escaping into the intergalactic medium (IGM). Galactic outflows can…
Large reservoirs of cold (~ 10^4 K) gas exist out to and beyond the virial radius in the circumgalactic medium (CGM) of all types of galaxies. Photoionization modeling suggests that cold CGM gas has significantly lower densities than…
Cosmic-rays constitute the main ionising and heating agent in dense, starless, molecular cloud cores. We reexamine the physical quantities necessary to determine the cosmic-ray ionisation rate (especially the cosmic ray spectrum at E < 1…
Cosmic rays provide an important source for free electrons in the Earth's atmosphere and also in dense interstellar regions where they produce a prevailing background ionization. We utilize a Monte Carlo cosmic ray transport model for…
Cosmic rays are the main agents in controlling the chemical evolution and setting the ambipolar diffusion time of a molecular cloud. We summarise the processes causing the energy degradation of cosmic rays due to their interaction with…
As long as magnetic fields remain frozen into the gas, the magnetic braking prevents the formation of protostellar discs. This condition is subordinate to the ionisation fraction characterising the inmost parts of a collapsing cloud. The…
Cosmic-ray and X-ray heating are derived from the electron energy loss calculations of Dalgarno, Yan and Liu for hydrogen-helium gas mixtures. These authors treated the heating from elastic scattering and collisional de-excitation of…
The first billion years in the evolution of the Universe mark the formation of the first stars, black holes and galaxies. The radiation from the first galaxies plays an important role in determining the final state of primordial gas…
Cosmic rays are an important source of heating in the interstellar medium, in particular in dense molecular cloud cores shielded from the external ultraviolet radiation field. The limits placed on the cosmic-ray ionization rate from…