The effect of ram pressure on the star formation, mass distribution and morphology of galaxies

Abstract

Aims. We investigate the dependence of star formation and the distribution of the components of galaxies on the strength of ram pressure. Several mock observations in X-ray, Hα and HI wavelength for different ram-pressure scenarios are presented. Methods. By applying a combined N-body/hydrodynamic description (GADGET-2) with radiative cooling and a recipe for star formation and stellar feedback 12 different ram-pressure stripping scenarios for disc galaxies were calculated. Special emphasis was put on the gas within the disc and in the surroundings. All gas particles within the computational domain having the same mass resolution. The relative velocity was varied from 100 km s −1 to 1000 km s −1 in different surrounding gas densities in the range from 1 × 10 −28 to 5 × 10 −27 g/cm 3 . The temperature of the surrounding gas was initially 1 × 10 7 K. Results. The star formation of a galaxy is enhanced by more than a magnitude in the simulation with a high ram-pressure (5 × 10 −11 dyn/cm 2 ) in comparison to the same system evolving in isolation. The enhancement of the star formation depends more on the surrounding gas density than on the relative velocity. Up to 95% of all newly formed stars can be found in the wake of the galaxy out to distances of more than 350 kpc behind the stellar disc. Continuously stars fall back to the old stellar disc, building up a bulge-like structure. Young stars can be found throughout the stripped wake with surface densities locally comparable to values in the inner stellar disc. Ram-pressure stripping can shift the location of star formation from the disc into the wake on very short timescales. As the gas in a galaxy has a complex velocity pattern due to the rotation and spiral arms, the superposition of the internal velocity field and the ram pressure causes complex structures in the gaseous wake which survive dynamically up to several 100 Myr. Finally we provide simulated X-ray, Hα and HI observations to be able to compare our results with observations in these wavebands. These simulated observations show many features which depend strongly both on the strength and the duration of the external ram pressure.

The rise and fall of star formation in z ∼ 0.2 merging galaxy clusters

“…For example, models of ram pressure stripping indicate that star-formation in galaxies within merging clusters can be quenched (e.g. Kapferer et al 2009). More recently, hydrodynamical simulations of shocks passing through galaxies have reproduced star-forming tails trailing behind their parent galaxy (Roediger et al 2014).…”

Search for cold and hot gas in the ram pressure stripped Virgo dwarf galaxy IC 3418

“…Higher-density gas with Σ ISM up to ∼ 50 M ⊙ pc −2 then can be accelerated from outer radii only, while the densest (molecular) gas stays bound to the galaxy. However, stripping by dynamical pressure of the ICM is probably enhanced by other processes such as ablation of dense clouds disrupted by hydrodynamic instabilities (e.g., Quilis et al 2000;Kapferer et al 2009;Tonnesen & Bryan 2009), or shockheating and dissociation of molecular clouds due to supersonic motion of IC3418 through the Virgo ICM (e.g., Guillard et al 2012). Moreover, the structure of the ISM in dwarf irregulars can be significantly influenced by stellar feedback and often contains up to ∼kpc-scale shells and holes seen in H i (see, e.g., Zhang et al 2012, and references therein), which could facilitate stripping of the ISM as was shown in numerical simulations of Quilis et al (2000) with holey disks.…”

The long X-ray tail in Zwicky 8338

“…Simulations in Kapferer et al (2009) show that for a relative velocity between the surrounding gas and the galaxy of v rel = 1000 km s −1 and pressure that is eight times higher and surrounding density that is six times higher, the scenario of a completely stripped gaseous disk can be explained. This might be a hint that the relative velocity of the galaxy is significantly larger.…”

“…Part of the gas from the galaxy is then used for new stars, either in the galactic halo or outside the galaxy in the ICM (see, e.g., Sun et al 2007). Simulations of the interaction between ISM and ICM (e.g., Stevens et al 1999;Kapferer et al 2009;Steinhauser et al 2012;Roediger et al 2015) predict a leading bow shock and tail behind the galaxy, which are both visible in X-rays. The highest chance to find these structures is in cool nearby clusters with blue galaxies.…”