Analysis of Some Parameters and of Possible Types of Shocks in a New Sample of Spitzer/GLIMPSE/EGO Regions of Formation of Massive Stars

详细

A comparative analysis is presented for the physical parameters of gas in various types of molecular clouds, derived from observations and theoretical calculations. Cool, dense fragments of infrared dense clouds (IRDCs)—rare star-forming regions with OH radical emission in the 1720-MHz satellite line, extended green objects (EGOs)— diffuse bipolar outflows discovered by the Spitzer mission at short IR wavelengths, and gas-dust condensations hosting class I and II methanol masers (class I MM and class II MM) are considered. The magnetic fields of these regions are calculated using the empirical criterion of Crutcher (ApJ, 520, 706, 1999) and the equation for numerical modeling of cold turbulent clouds of Ostriker et al. (ApJ, 546, 980, 2001). This modeling is done for three values of the parameter β = (cs/cA)² relating the sound and Alfvén speeds, which describes the effect of the magnetic field: strong (β = 0.01), intermediate (β = 0.1), and weak (β = 1). In 69 EGOs with densities of 10⁴–10^5.6 cm⁻³, derived earlier from observations, and with an acceptable temperature range, from T_k ≈ 30 K to T_k ≈ 100 K, the results of the calculations are most consistent with β = 0.1 (|B̄|= 0.26 mG) and β = 1 (|B̄|= 0.15 mG) for intermediate and weak magnetic fields, respectively. For class I methanol masers, with gas densities not exceeding 10⁶ cm⁻³ and a temperature T_k = 80 K, the most plausible value is β = 1 (|B < 0.4 mG), i.e., the expected effect of the magnetic field is weak. Comparison of the sound and Alfvén speeds suggests that very faint, low-velocity C-type shocks may exist in these objcts, with the magnetic field exerting little control over the chaotic motions of the material. The shocks are continuous, and do not affect the parameters in the maser condensations. The magnetic intensities found for class I MMs and OH (1720 MHz) regions differ only slightly; according to this parameter, which is related to the density of the medium and the kinetic temperature of the gas, they may be observed in either different or the same gas-dust condensations.