相关论文: Gas-phase recombination, grain neutralization and …
Low-energy cosmic rays are a fundamental source of ionization for molecular clouds, influencing their chemical, thermal and dynamical evolution. The purpose of this work is to explore the possibility that a low-energy component of…
After recombination the cosmic gas was left in a cold and neutral state. However, as the first stars and black holes formed within early galactic systems, their UV and X-ray radiation induced a gradual phase transition of the intergalactic…
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…
The D/H ratio in interstellar gas varies on scales of a few hundred pc in the local Milky Way, with D/H values ranging from ~7 ppm to ~22 ppm. The reduction in D/H relative to the primordial value of D/H (~ 26 ppm) is usually attributed to…
The molecular gas in the Central Molecular Zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H$_3^+$ lines at 3.5-4.0 $\mu$m and CO lines near 2.34 $\mu$m. In addition to the previously reported spectra of these…
We present numerical computations and analysis of atomic to molecular (HI-to-H$_2$) transitions in cool ($\sim$100 K) low-metallicity dust-free (primordial) gas, in which molecule formation occurs via cosmic-ray driven negative ion…
We use an analytic model to study how inhomogeneous hydrogen reionization affects the temperature distribution of the intergalactic medium (IGM). During this process, the residual energy of each ionizing photon is deposited in the IGM as…
The line ratios from coronal gas in Seyferts can be successfully fitted with photoionized clouds of high densities and low volume filling factor. The ionization parameter implied is sufficiently high that models must consider the effect of…
The typical amount of molecular hydrogen (${\rm H_2}$) in interstellar ices is not known, but significant freeze-out of ${\rm H_2}$ on dust grains is not expected. However, chemical models ubiquitously predict large amounts of $\rm H_2$…
We model gas cooling in high-resolution N-body simulations in order to investigate the formation of the first generation of stars. We follow a region of a LCDM universe especially selected to contain a rich cluster by the present day. The…
We present new computations of the equilibrium and non-equilibrium cooling efficiencies and ionization states for low-density radiatively cooling gas containing cosmic abundances of the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe. We…
We analyze the hydrostatic effect of AGN radiation pressure on optically thick gas in the host galaxy. We show that in luminous AGN, the radiation pressure likely confines the ionized layer of the illuminated gas. Radiation pressure…
Cosmic rays (CR) play an important role in dense molecular cores, affecting their thermal and dynamical evolution and initiating the chemistry. Several studies have shown that the formation of protostellar discs in collapsing clouds is…
Surface tension of small grains and droplets makes them stable only at a much lower temperature than in bulk. This makes spontaneous nucleation unfavorable in many cases. Kinetic approaches are delicate in that one can easily generate…
The critical star formation rate density required to keep the intergalactic hydrogen ionised depends crucially on the average rate of recombinations in the intergalactic medium (IGM). This rate is proportional to the clumping factor C =…
One of the most outstanding problems in the gravitational collapse scenario of early structure formation is the cooling of primordial gas to allow for small mass objects to form. As the neutral primordial gas is a poor radiator at…
Grain growth by accretion of gas-phase metals is a common assumption in models of dust evolution, but in dense gas, where the timescale is short enough for accretion to be effective, material is accreted in the form of ice mantles rather…
We develop and test with cosmological simulations a physically motivated theory for how the interplay between gravity, pressure, cooling, and self-shielding set the redshift--dependent mass scale at which halos can accrete intergalactic…
We report a strong correlation between the [CII] 158 micron cooling line and the mid-infrared flux in the 5-10 micron range in a wide variety of star-forming galaxies. The mid-infrared flux is dominated by Aromatic Feature Emission (AFE),…
Sightlines through high- and intermediate-velocity clouds allow measurements of ionic gas phase abundances, A, at very low values of HI column density, N(HI). Present observations cover over 4 orders of magnitude in N(HI). Remarkably, for…