Simulations of gas clouds in interacting galaxies

A companion can induce a variety of morphological changes in a galaxy. The author uses N-body simulations to study the effects of different kinds of perturbations on the dynamics of a disk galaxy. The model is two-dimensional, with a disk consisting of about 60,000 particles. Most of the particles (80%) represent the old stellar population with a high velocity dispersion, while the rest (20%) represent gas clouds with a low velocity dispersion. Initially, the velocity dispersion corresponds to Q = 1 for the star particles, and Q = O for the gas particles, where Q is Toomre's (1964) stability parameter. The gas clouds can collide inelastically. The disk is stabilized by a rigid halo potential, and by the random motions of the old star particles. To simulate the effect of an encounter on the disk, a companion galaxy, modelled as a point mass, can move in a co-planar orbit around the disk. A complete description of the N-body code is found in Thomasson (1989). The spiral structures caused by a companion in first a direct and then a retrograde (with respect to the rotation of the disk) parabolic orbit are presented. The associated velocity fields suggest a way to observationally distinguish between leading and trailing spiral arms. The stability of the gas component in a disk in which tidally triggered infall of gas to the center occurs is studied. Finally, the author shows how a ring of gas can form in a disk as a result of a co-planar encounter with another galaxy

Formation of massive clouds and dwarf galaxies during tidal encounters

Gerola et al. (1983) propose that isolated dwarf galaxies can form during galaxy interactions. As evidence of this process, Mirabel et al. (1991) find 10(exp 9) solar mass clouds and star formation complexes at the outer ends of the tidal arms in the Antennae and Superantennae galaxies. We describe observations of HI clouds with mass greater than 10(exp 8) solar mass in the interacting galaxy pair IC 2163/NGC 2207. This pair is important because we believe it represents an early stage in the formation of giant clouds during an encounter. We use a gravitational instability model to explain why the observed clouds are so massive and discuss a two-dimensional N-body simulation of an encounter that produces giant clouds

Deuterated molecules in regions of high-mass star formation

We present the results of our studies of deuterated molecules (DCN, DNC, DCO$^+$, N$_2$D$^+$ and NH$_2$D) in regions of high-mass star formation, which include a survey of such regions with the 20-m Onsala radio telescope and mapping of several objects in various lines with the 30-m IRAM and 100-m MPIfR radio telescopes. The deuteration degree reaches $\sim$10$^{-2}$ in these objects. We discuss its dependencies on the gas temperature and velocity dispersion, as well as spatial distributions of deuterated molecules. We show that the H$^{13}$CN/HN$^{13}$C intensity ratio may be a good indicator of the gas kinetic temperature and estimate densities of the investigated objects.Comment: 8 pages, 4 figures, to be published in Proceedings of Science (Proceedings of the conference "The Multifaceted Universe: Theory and Observations - 2022", 23-27 May 2022, SAO RAS, Nizhny Arkhyz, Russia

IRAC and MIPS Observations of the Interacting Galaxies IC 2163 and NGC 2207: Clumpy Emission

IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologically peculiar region of star formation in the western arm of NGC 2207. This clump, which dominates the Halpha and radio continuum emission from both galaxies, accounts for ~12% of the total 24mu m flux. Nearly half of the clumps are regularly spaced along some filamentary structure, whether in the starburst oval of IC 2163 or in the thin spiral arms of NGC 2207. This regularity appears to influence the clump luminosity function, making it peaked at a value nearly a factor of 10 above the completeness limit, particularly in the starburst oval. This is unlike the optical clusters inside the clumps, which have a luminosity function consistent with the usual power law form. The giant IR clumps presumably formed by gravitational instabilities in the compressed gas of the oval and the spiral arms, whereas the individual clusters formed by more chaotic processes, such as turbulence compression, inside these larger-scale structures.Comment: 49 pages, 18 figures, ApJ, 642, 15

Kan man \ue5ka raka sp\ue5ret till Merkurius? M\uf6jliga och om\uf6jliga resv\ue4gar i solsystemet

Merkuriussonden Messenger fick g\uf6ra en l\ue5ngresa under m\ue5nga \ue5r. Det \ue4r inte l\ue4tt att f\ue4rdas till andraplaneter, och om de ligger n\ue4ra kan det vara knepigare \ue4nom de ligger l\ue5ngt bort