Theoretical Astrophysics Cologne

Impact of B fields and radiative feedback on CO emission
Column density of hydrogen nuclei (top) and CO (bottom) for two runs without magnetic fields without (left) and with feedback (middle), and one run with magnetic fields (right). CO shows a significantly more compact distribution than that of the total gas leading to a significant amount of CO-dark gas, in particular in the outer regions of the clouds. (Read details)

Gas expulsion from young star clusters
Gas expulsion from an embedded star cluster of total mass $3 \times 10^3 M_{\odot}$. The cluster features the model which is resolved to individual stars: massive stars are shown by blue asterisks, lower mass stars are represented by circles. The panels show: density (upper left); pressure (upper right); temperature (lower left); and velocity (lower right). Feedback sweeps the cloud to a network of sheets, filaments and semi-shells, which are gradually eroded and pushed from the cluster centre, clearing the cluster of gas on a time-scale of $1$ Myr. (Read details)

Observation of supernova remnant interacting with molecular cloud
An intensity map of CTB 109 taken from a mosaic of images observed with XMM-Newton. The green contours show the integrated intensity of 12CO (J=1-0) line taken from the Canadian Galactic Plane Survey. The white box shows the region observed using the IRAM 30m telescope. (Read details)

Supernova driven supersonic turbulence in molecular clouds
Evolution of the velocity dispersion of the modelled molecular cloud subjected to SNe (dashed lines) and without SNe (solid lines). The velocity dispersion is measured in $^{12}$CO (blue lines), $^{13}$CO (orange lines) and C$^{18}$O (green lines). The black vertical lines indicate the time when the SNe occur. The panels from right to left correspond to the sightlines along directions $x$, $y$ and $z$, respectively. (Read details)

Suppression of CO clump formation by magnetic fields
The time-averaged (between $18-22$ Myr) clump mass function for colliding flow simulations with different magnetic field strength $B$. All the mass functions are normalised to the unit mass. (Read details)

Polarisation degree at different wavelengths
olarisation degree at different wavelengths as calculated by the POLARIS code on the SILCC zoom-in simulation. The simulation contains an O star at the centre. The numbers at the upper right corners indicate the particular wavelength in $\mu$m. The polarisation depends on the wavelength, and it is most conspicuous at wavelength $515$ $\mu$m. (Read details)

Synthetic CO emission maps from the SILCC zoom-in simulations
From top left to lower right, the panels show simulations with increasing resolution from 3.9 to 0.06 pc. The black contours indicate the observable area where the integrated intensity is above 0.1 K km/s. The point of the highest integrated intensity is shown by a cross, the value of which is listed in the legend. (Read details)

Evolution of Hubble wedges in episodic protostellar outflows
Smooth particle hydrodynamics simulation of a collapsing $ 1.0 \, \mathrm{M}_{\odot}$ turbulent core, surrounded by a low-density envelope. The simulation features formation of a stable triple system consisting of a close binary with a more distant companion. All three stars eject episodic outflow bullets. In the early high-accretion phase, the outflows point in various directions. As the system settles, all outflow axes align forming a single massive outflow. (Read details)

Shock Capturing using the Meshless Method
Radial density profile in a standard Sedov blast wave test using different methods with $\sim 200,000$ particles at $t=0.06$. Plotted is the relative density against the dimensionless radius $\xi$. The two flavours of the meshless finite method ( red = MFV and black = MFM) show a sharper shock front compared to SPH (green). The simulations were performed by the fluid dynamical code GANDALF. (Read details)

Star formation and feedback in molecular clouds
Image Credit: Stefan Reissl. Image created with the help of the POLARIS code (Reissl et al., 2018, 2018ascl.soft07001R) based on simulation data from Haid et al. (2019) MNRAS, 482, 4062. The colour composite shows red: H$_{\alpha}$, green: C$^+$ , blue: CO (1-0). (Read details)

The charge distribution of dust grains in the interstellar medium
Dust grains may be neutral, positively or negatively charged, and this charge influences their effect on the thermal, chemical and dynamic properties of the ISM. Charging dust grains may be accomplished by sticking collision with ions and electrons, positively and negatively charging the grain, or by radiative charging, positively charging the grains by ejecting photoelectrons. We investigate the charge distribution of a dust grain population in the warm, cold and molecular phases of the ISM, and derive a new set of parametric equations to reconstruct the charge distribution of a dust grain as a function of its size, composition and its environmental properties. (Read details)

Synthetic dust polarisation maps of simulated molecular clouds
Effect of noise (middle panel) and subsequent convolution (right panel) on the polarisation pattern of a simulated molecular cloud. Noise randomizes the polarisation structure compared to the structure without noise (left panel) in regions of low intensity. Convolution helps to improve the quality of the polarisation data in regions with intensities above a few times the noise level as indicated by the magenta line. In the high-intensity regions, the polarisation structure is well preserved even for the noisy image. (Read details)

Numerical simulations of a molecular cloud with star formation and ionising radiation
Numerical simulation of a molecular cloud self-consistently forming out of a multi-phase interstellar medium. The cloud forms stars (massive stars are shown by white symbols; lower mass stars by black circles), the massive of them emit photo-ionising radiation. The radiative stellar feedback heats the gas (mass-weighted temperature, right panel) dispersing the cloud (integrated density, left panel), showing the importance of radiative feedback on molecular cloud evolution. (Read details)

Synthetic observations of fibrous filaments: the problems of mapping from PPV to PPP
A movie showing the PPV cube of synthetic C$^{18}$O observations of fragmenting filaments. There exists significant sub-structure which is well separated in velocity space, similar to the `fibres' detected in Taurus. However, the origin of the emission which constitutes these fibres is not related to discreet density structures in PPP space. Therefore, one should be cautious when studying the properties of velocity-coherent and discreet structures in PPV space as they may have no relation to real PPP structures. (Read details)

Implementing Radiation Pressure into the AMR code FLASH
Vertical density profile (left panel) and local heating intensity (right panel) for a model of plan-parallel radiation and optically thin ($\tau \ll 1$) medium. The radiation is coming from the negative $z$-direction. The model has periodic boundary conditions in the $x$- and $y$-direction, and outflow and reflecting conditions in the positive and negative $z$ directions, respectively. The density evolves close to the analytic exponential profile (the analytic solution is indicated by a dashed line). The right panel shows that the local heating intensity is plan-parallel to the edge, thus it follows well the periodic boundary conditions. (Read details)

Virial Analysis of Molecular Clumps Forming in Colliding Flows
Ternary diagram comparing the absolute values of the terms. in the Eulerian virial theorem, evaluated for clumps detected at 20 Myr. $E_{mhd}$ is the sum of the thermal, kinetic and magnetic energy, $W$ is the potential energy due to self-gravity and $\Phi$ is the flux of moment of inertia through the surface. For many clumps, the time-dependent $\Phi$-term dominates. (Read details)

Implementing Hermite predictor-corrector integrator to AMR code FLASH
A density plot of a simulation using the Hermite integrator. The simulation studies ten star clusters, each containing 1000 stars, which are initially embedded inside a molecular cloud. The clusters merge due to gravitational attraction, and photoionise the cloud at the same time. (Read details)

A new entropy stable magnetohydrodynamic solver for astrophysical purposes
Projection plot of the magnetic field strength in the colliding flow setup. As can be seen, the mean magnetization is notably higher in the solution obtained using our new scheme. This is in agreement with reference solutions computed using constrained transport (CT) methods. As CT schemes are much more computationally intense, they are in general unsuitable for computing multi-physics simulations as we aim to do in Astrophysics. (Read details)

Synthetic Column Density Map Based on Dust
Synthetic column density map based on dust emission for SILCC zoom-in simulations.(Read details)

Origin of the [CII] line emission in molecular clouds
Simulated forming molecular cloud before the onset of star formation. The panels show the column density of the total gas (upper left), the column densities of molecular hydrogen (H$_2$, lower left), atomic hydrogen (H, upper right), and the integrated [CII] line emitted from the carbon ions C$^+$ (lower right). (Read details)