arXiv subjects

Mika Juvela

Publications and source records attributed to Mika Juvela.

128 records · Page 8Linked to original sources

arXiv1997

Supersonic Random Flows in the Perseus Molecular Cloud

We compare the statistical properties of J=1-0 13CO spectra observed in the Perseus Molecular Cloud with synthetic J=1-0 13CO spectra from a 5 pc model cloud. The synthetic spectra are computed solving the non-LTE radiative transfer problem for a model cloud obtained as solutions of the 3-D magneto-hydrodynamic (MHD) equations in both the highly supersonic and super-Alfvenic regimes of random flows. We present several statistical results that demonstrate remarkable similarity between real data and the synthetic cloud. The three-dimensional structure and dynamics of molecular clouds like Perseus are appropriately described by random supersonic and super-Alfvenic MHD flows. Although the description of gravity and stellar radiation are essential to understand the formation of single protostars and the effects of star formation in the cloud dynamics, the overall description of the cloud and of the initial conditions for star formation can apparently be described on intermediate scales without accounting for gravity and stellar radiation.

astro-ph↗

arXiv1997

A Theoretical Calibration of ^{13}CO LTE Column Density in Molecular Clouds

In this work we use models of molecular clouds (MC), and non-LTE radiative transfer calculations, to obtain a theoretical calibration of the relation between LTE 13CO column density and true column density in MCs. The cloud models consist of 3 dimensional grids of density and velocity fields obtained as solutions of the compressible magneto-hydrodynamic equations in a 128x128x128 periodic grid in both the supersonic and super-Alfvenic regimes. Due to the random nature of the velocity field and the presence of shocks, the density spans a continuous range of values covering over 5-6 orders of magnitude (from ~0.1 to ~10^5 cm^-3). As a result, the LTE column density can be calibrated over 3 orders of magnitude. We find that LTE column density of molecular clouds typically underestimates the mean 13CO true column density by a factor ranging from 1.3 to 7. These results imply that the standard LTE methods for the derivation of column densities from CO data systematically underestimate the true values independent of other major sources of uncertainty such as the relative abundance of CO.

astro-ph↗