T. Kronberger

On the influence of ram-pressure stripping on the star formation of simulated spiral galaxies

Aims. We investigate the influence of ram-pressure stripping on the star formation and the mass distribution in simulated spiral galaxies. Special emphasis is put on the question of where the newly formed stars are located. The stripping radius from the simulation is compared to analytical estimates. Methods. Disc galaxies are modelled in combined N-body/hydrodynamic simulations (GADGET-2) with prescriptions for cooling, star formation, stellar feedback, and galactic winds. These model galaxies move through a constant density and temperature gas, which has parameters comparable to the intra-cluster medium (ICM) in the outskirts of a galaxy cluster (T = 3k eV≈ 3.6 × 10 7 K and ρ = 10 −28 g/cm 3 ). With this numerical setup we analyse the influence of ram-pressure stripping on the star formation rate of the model galaxy. Results. We find that the star formation rate is significantly enhanced by the ram-pressure effect (up to a factor of 3). Stars form in the compressed central region of the galaxy, as well as in the stripped gas behind the galaxy. Newly formed stars can be found up to hundred kpc behind the disc, forming structures with sizes of roughly 1 kpc in diameter and with masses of up to 10 7 M� .A s they do not possess a dark matter halo due to their formation history, we name them “stripped baryonic dwarf” galaxies. We also find that the analytical estimate for the stripping radius from a Gunn & Gott (1972) criterion agrees well with the numerical value from the simulation. Like in former investigations, edge-on systems lose less gas than face-on systems, and the resulting spatial distribution of the gas and the newly formed stars is different.

Metal Enrichment Processes in the Intra-Cluster Medium

Institut fu¨r Astronomie, Universit¨at Wien, Tu¨rkenschanzstr. 17, 1180 Vienna, AustriaReceived / AcceptedAbstract. We present numerical simulations of galaxy clusters which include interaction processes between thegalaxies and the intra-cluster gas. The considered interaction processes are galactic winds and ram-pressurestripping, which both transfer metal-enriched interstellar medium into the intra-cluster gas and hence increase itsmetallicity. We investigate the efficiency and time evolution of the interaction processes by simulated metallicitymaps, which are directly comparable to those obtained from X-ray observations. We find that ram-pressurestripping is more efficient than quiet (i.e. non-starburst driven) galactic winds in the redshift interval between 1and 0. The expelled metals are not mixed immediately with the intra-cluster gas, but inhomogeneities are visiblein the metallicity maps. Even stripes of higher metallicity that a single galaxy has left behind can be seen. Thespatial distribution of the metals transported by ram-pressure stripping and by galactic winds are very differentfor massive clusters: the former process yields a centrally concentrated metal distribution while the latter resultsin an extended metal distribution.Key words. Galaxies:clusters:general – Galaxies:abundances – Galaxies:interactions – Galaxies:ISM – X-ray:galaxies:clusters

On the influence of ram-pressure stripping on interacting galaxies in clusters

We investigate the influence of ram pressure on the star-formation rate and the distribution of gas and stellar matter in interacting model galaxies in clusters. To simulate the baryonic and non-baryonic components of interacting disc galaxies moving through a hot, thin medium, we use a combined N-body/hydrodynamic code GADGET2 with a description for star formation based on density thresholds. Two identical model spiral galaxies on a collision trajectory with three different configurations were investigated in detail. In the first configuration, the galaxies collide without the presence of an ambient medium. In the second configurations, the ram pressure acts face-on on the interacting galaxies and in the third configuration the ram pressure acts edge-on. The ambient medium is thin (10 −28 gc m −3 ), hot (3 keV ≈ 3.6 × 10 7 K) and has a relative velocity of 1000 km s −1 , to mimic an average low ram pressure in the outskirts of galaxy clusters. The interaction velocities are comparable to galaxy interactions in groups, falling along filaments into galaxy clusters. The global star-formation rate of the interacting system is enhanced in the presence of ram pressure by a factor of 3 in comparison to the same interaction without the presence of an ambient medium. The tidal tails and the gaseous bridge of the interacting system are almost completely destroyed by the ram pressure. The amount of gas in the wake of the interacting system is ∼50 per cent of the total gas of the colliding galaxies after 500 Myr the galaxies start to feel the ram pressure. Nearly ∼10– 15 per cent in mass of all newly formed stars are formed in the wake of the interacting system at distances larger than 20 kpc behind the stellar discs. As the tidal tails and the gaseous bridge between the interacting systems feel the ram pressure, knots of cold gas (T < 1 × 10 5 K) start

Metal enrichment of the intra-cluster medium over a Hubble time for merging and relaxed galaxy clusters

We investigate the efficiency of galactic mass loss, triggered by ram-pressure stripping and galactic winds of cluster galaxies, on the chemical enrichment of the intra-cluster medium (ICM). We combine N -body and hydrodynamic simulations with a semi-numerical galaxy formation model. By including simultaneously different enrichment processes, namely ram-pressure stripping and galactic winds, in galaxy-cluster simulations, we are able to reproduce the observed metal distribution in the ICM. We find that the mass loss by galactic winds in the redshift regime

X-ray measured metallicities of the intra-cluster medium: a good measure for the metal mass?

z>2

Metal enrichment of the intra-cluster medium by thermally and cosmic-ray driven galactic winds - An analytical prescription for galactic outflows

is ~10% to 20% of the total galactic wind mass loss, whereas the mass loss by ram-pressure stripping in the same epoch is up to 5% of the total ram-pressure stripping mass loss over the whole simulation time. In the cluster formation epochs

Internal kinematics of spiral galaxies in distant clusters - III. Velocity fields from FORS2/MXU spectroscopy

z<2

Distant Galaxy Transformation Probed by VLT and HST

ram-pressure stripping becomes more dominant than galactic winds. We discuss the non-correlation between the evolution of the mean metallicity of galaxy clusters and the galactic mass losses. For comparison with observations we present two dimensional maps of the ICM quantities and radial metallicity profiles. The shape of the observed profiles is well reproduced by the simulations in the case of merging systems. In the case of cool-core clusters the slope of the observed profiles are reproduced by the simulation at radii below ~300 kpc, whereas at larger radii the observed profiles are shallower. We confirm the inhomogeneous metal distribution in the ICM found in observations. To study the robustness of our results, we investigate two different descriptions for the enrichment process interaction.

Metal Enrichment Processes in the ICM – Starbursts and Galactic Winds

Aims. We investigate whether X-ray observations map heavy elements in the Intra-Cluster Medium (ICM) well and whether the X-ray observations yield good estimates for the metal mass, with respect to predictions on transport mechanisms of heavy elements from galaxies into the ICM. We further test the accuracy of simulated metallicity maps. Methods. We extract synthetic X-ray spectra from N-body/hydrodynamic simulations including metal enrichment processes, which we then analyse with the same methods as are applied to observations. By changing the metal distribution in the simulated galaxy clusters, we investigate the dependence of the overall metallicity as a function of the metal distribution. In addition we investigate the difference of X-ray weighted metal maps produced by simulations and metal maps extracted from artificial X-ray spectra, which we calculate with SPEX2.0 and analyse with XSPEC12.0. Results. The overall metallicity depends strongly on the distribution of metals within the galaxy cluster. The more inhomogeneously the metals are distributed within the cluster, the less accurate is the metallicity as a measure for the true metal mass. The true metal mass is generally underestimated by X-ray observations. The difference between the X-ray weighted metal maps and the metal maps from synthetic X-ray spectra is on average less than 7% in the temperature regime above T > 3 × 10 7 K, i.e. X-ray weighted metal maps can be well used for comparison with observed metal maps. Extracting the metal mass in the central parts (r < 500 kpc) of galaxy clusters with X-ray observations results in metal mass underestimates up to a factor of three.

Internal Kinematics of Modelled Isolated and Interacting Disc Galaxies

Aims. We investigate the efficiency and time-dependence of thermally and cosmic ray driven galactic winds for the metal enrichment of the intra-cluster medium (ICM) using a new analytical approximation for the mass outflow. The spatial distribution of the metals are studied using radial metallicity profiles and 2D metallicity maps of the model clusters as they would be observed by X-ray telescopes like XMM-Newton. Methods. Analytical approximations for the mass loss by galactic winds driven by thermal and cosmic ray pressure are derived from the Bernoulli equation and implemented in combined N-body/hydrodynamic cosmological simulations with a semi-analytical galaxy formation model. Observable quantities like the mean metallicity, metallicity profiles, and 2D metal maps of the model clusters are derived from the simulations. Results. We find that galactic winds alone cannot account for the observed metallicity of the ICM. At redshift z = 0 the model clusters have metallicities originating from galactic winds which are almost a factor of 10 lower than the observed values. For massive, relaxed clusters we find, as in previous studies, a central drop in the metallicity due to a suppression of the galactic winds by the pressure of the ambient ICM. Combining ram-pressure stripping and galactic winds we find radial metallicity profiles of the model clusters which agree qualitatively with observed profiles. Only in the inner parts of massive clusters the observed profiles are steeper than in the simulations. Also the combination of galactic winds and ram-pressure stripping yields too low values for the ICM metallicities. The slope of the redshift evolution of the mean metallicity in the simulations agrees reasonably well with recent observations.