Ram pressure stripping of galaxies (with continuous mass loss)
Joachim Köppen Kiel March 2017

### Some brief explanations

• This utility allows the user to estimate the consequences of ram pressure stripping on the gas disk of a galaxy, while also accounting for a ram pressure-induced continuous mass loss.
• On its path towards the centre of a galaxy cluster an infalling galaxy experiences an increasing ram pressure, due to the increase of the density of the hot intracluster medium and the increase of its velocity. Thus the outer radius of the gas disk shrinks along the path, reaching a mimimum value when the maximum pressure is reached at the closest approach to the cluster centre. The kinematical criterion by Gunn & Gott (1972) describes well the response of the gas disk to ram pressure, in the limit of the pressure to last sufficiently long. Thus the state of the gas disk as a function of the instantaneous pressure approximates the outcome of ram pressure stripping events at various pressure levels. This approach is used in this utility. A further assumption is that the ram pressure acts always perpendicularly to the galaxy's plane ('face-on stripping').
• The galaxy is specified by these parameters:
(Green background indicates a valid input field)
• rotation speed: as spiral galaxies usually have flat rotation curves, a single value suffices to characterize the gravitational potential. The maximum restoring force in the criterion of Gunn & Gott can well be appriximated by the centrifugal force.
• optical radius: to be used in future extensions of the simulation.
• exponential disk profile: specifies the type of profile for the surface density in the gas disk. The other option is a Kuzmin profile.
• gas disk radius: is the initial outer radius of the gas disk.
• gas radial scale: is the parameter for the disk profile.
• cent.surf.density: specifies of shows the gas surface density at the galactic centre ...
• gas mass: gives or specifies the total gas mass. A click on this field allows to enter data here, as indicated by the green background.
• cont.mass loss coeff.: specifies the continuous mass loss rate that the remaining gas disk undergoes. It is assumed that the mass loss rate of a gas element is proportional to its surface density and to the instantaneous ram pressure. This constant is in units of 1/(1000 Myr cm-3 (km/s)²).
• The ram pressure pulse (modeled as a Lorentzian function) is characterized by:
• max.pressure: is the maximum value.
• pulse duration: its FWHM duration
• The display is controlled by:
• X, Y: chose the abscissa and the ordinate among:
• time: shown is the evolution during the span of 10 pulse durations, before the peak pressure. After that moment the gas disk radius no longer changes and thus is of no further interest in this simulation
• ram pressure
• time integrated ram pressure AKA (vΣ)ICM
• gas radius: the truncation radius of the remaining gas disk. This would the stripping radius in the stricter sense that it denotes the border between gas that is escapes from the galaxy and the gas that remains gravitationally bound. Note that the latter would include gas lifted above the disk eventually falling back.
• gas mass: the mass inside the gas radius
• mass loss rates: for the entire galaxy: the total rate (red) and the one for continuous mass loss (blue).
• gas mass fraction: the fraction of the inital mass that remains.
• deficiency = log10(initial mass/remaining mass).
• mean surface density = remaining mass / (π gas_radius²).
• wipe&plot: clear the plot area and draws the last curve in red. Changing any parameter value (and hitting the Enter key) will overplot the new curve in red.
• overplot: after changing any parameter value, these button will overplot the new curve in the corresponding colour.

rotation speed [km/s]