GMC Collisions as Triggers of Star Formation. II. 3D Turbulent, Magnetized Simulations

We investigate giant molecular cloud (GMCs) collisions and their ability to induce gravitational instability and thus star formation. This mechanism may be a major driver of star formation activity in galactic disks. We carry out a series of three dimensional, magnetohydrodynamics (MHD), adaptive mesh refinement (AMR) simulations to study how cloud collisions trigger formation of dense filaments and clumps. Heating and cooling functions are implemented based on photo-dissociation region (PDR) models that span the atomic to molecular transition and can return detailed diagnostic information. The clouds are initialized with supersonic turbulence and a range of magnetic field strengths and orientations. Collisions at various velocities and impact parameters are investigated. Comparing and contrasting colliding and non-colliding cases, we characterize morphologies of dense gas, magnetic field structure, cloud kinematic signatures, and cloud dynamics. We present key observational diagnostics of cloud collisions, especially: relative orientations between magnetic fields and density structures, like filaments; 13CO(J=2-1), 13CO(J=3-2), and 12CO(J=8-7) integrated intensity maps and spectra; and cloud virial parameters. We compare these results to observed Galactic clouds

A global view of stellar populations in M82

Abstract We present photometric and spectroscopic studies of the stellar content of M82, including the resolved halo stellar population and the halo globular clusters. M82 is a nearby peculiar galaxy that recently went through a close encounter with its more massive companion, M81. As a result, M82 has a high star formation activity and unusual stellar content. We studied the resolved stellar population using the imaging data from the Hubble Space Telescope (HST) data archive. Then, their metallicities were analyzed to understand a global view of the stellar populations in M82. We found that the old stellar population in M82 shows typical characteristics for a disk galaxy, while the young stellar population shows a sign of disruption as a result of the recent interactions.</jats:p

Physical properties of RR Lyrae variables in Galactic globular clusters and dwarf spheroidal galaxies

Abstract We propose a tool to distinguish between Galactic globular clusters (GCs) and dwarf galaxies based on physical properties of RR Lyrae (RRL) variables in the systems. Normally, these two systems show various distinctive properties; for instance, mass, size, and luminosity. Nevertheless, these properties overlap each other in recently discovered systems. The subsequent classification between GCs and dwarf spheroidal (dSph) galaxy is ambiguous. An RRL variable is a pulsating variable star with a short period of 0.2-1 days. It is relatively easy to observe the complete period of its light curve. The age of RRL stars is typically more than 10 Gyr; therefore, they can provide information of the host system at its early stage. In this study, we provide an extensive data collection of RRLs in 96 GCs, 23 dSphs, and 10 dwarf irregular (dIrr) galaxies. Based on public catalogs, we analyze various RRL properties such as Oosterhoff dichotomy, fraction of high amplitude short period (HASP) variables, metallicity, and specific frequency of RRLs (SRR). We examine correlations among all properties in an attempt to distinguish between GCs and dSphs.</jats:p

A computational study of the gas-phase interstellar formose-like reactions

Abstract Understanding the extraterrestrial origin of ribose, as one of the sub-units of ribonucleic acid (RNA), is crucial to anticipating the formation of the building blocks of life under interstellar medium (ISM) conditions. Under ordinary atmospheric conditions, the formation of sugar is suggested to occur through the formose reaction, where formaldehyde is solely used as the precursor in each of the iterative steps of the formation process. On the other hand, sugar synthesis under ISM conditions has evidently been shown to be significantly different from the terrestrial formose reactions due to the extremely low density of molecules and the very low temperature. In this study, we theoretically investigate the formose-like reactions for ribose formation catalyzed by a single proton through the mean of computer simulation based on first-principles density functional theory (DFT). The ribose formation reactions are modelled in the absence of solvation effects at absolute zero temperature to mimic the extremely low pressure and temperature found in ISM. We observe that the presence of a proton gives rise to a more thermodynamically stable complex of the two reactive carbonyl compounds by bridging their oxygen atoms as required for the iterative formose reaction to proceed. In order to form a new carbon-carbon bond through an iterative process, only the region where the additional formaldehyde attaches to the existed protonated carbonyl compound is of great importance. The energy barriers for all the iterative steps during the ribose formation are similar, i.e., ∼67 kcal mol−1. Our findings show that a single proton can act as an efficient catalyst for the gas-phase ribose formation reactions in the absence of solvent effects. The results also suggest that ribose formation can preferentially occur via the formose pathway in the presence of protons, which are abundantly presented in ISM.</jats:p