Dark matter density profiles: A comparison of nonextensive theory with N-body simulations

Density profiles of simulated galaxy cluster-sized dark matter haloes are analysed in the context of a recently introduced nonextensive theory of dark matter and gas density distributions. Nonextensive statistics accounts for long-range interactions in gravitationally coupled systems and is derived from the fundamental concept of entropy generalisation. The simulated profiles are determined down to radii of ~1% of R_200. The general trend of the relaxed, spherically averaged profiles is accurately reproduced by the theory. For the main free parameter kappa, measuring the degree of coupling within the system, and linked to physical quantities as the heat capacity and the polytropic index of the self-gravitating ensembles, we find a value of -15. The significant advantage over empirical fitting functions is provided by the physical content of the nonextensive approach.Comment: 6 pages, 3 figures, accepted for publication in A&

Internal kinematics of isolated modelled disk galaxies

We present a systematic investigation of rotation curves (RCs) of fully hydrodynamically simulated galaxies, including cooling, star formation with associated feedback and galactic winds. Applying two commonly used fitting formulae to characterize the RCs, we investigate systematic effects on the shape of RCs both by observational constraints and internal properties of the galaxies. We mainly focus on effects that occur in measurements of intermediate and high redshift galaxies. We find that RC parameters are affected by the observational setup, like slit misalignment or the spatial resolution and also depend on the evolution of a galaxy. Therefore, a direct comparison of quantities derived from measured RCs with predictions of semi-analytic models is difficult. The virial velocity V_c, which is usually calculated and used by semi-analytic models can differ significantly from fit parameters like V_max or V_opt inferred from RCs. We find that V_c is usually lower than typical characteristic velocities derived from RCs. V_max alone is in general not a robust estimator for the virial mass.Comment: 9 pages, 15 figures, accepted for publication in A&

Internal kinematics of modelled interacting disc galaxies

We present an investigation of galaxy-galaxy interactions and their effects on the velocity fields of disc galaxies in combined N-body/hydrodynamic simulations, which include cooling, star formation with feedback, and galactic winds. Rotation curves (RCs) of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We show that galaxy-galaxy mergers and fly-bys disturb the velocity fields significantly and hence the RCs of the interacting galaxies, leading to asymmetries and distortions in the RCs. Typical features of disturbed kinematics are significantly rising or falling profiles in the direction of the companion galaxy and pronounced bumps in the RCs. In addition, tidal tails can leave strong imprints on the rotation curve. All these features are observable for intermediate redshift galaxies, on which we focus our investigations. We use a quantitative measure for the asymmetry of rotation curves to show that the appearance of these distortions strongly depends on the viewing angle. We also find in this way that the velocity fields settle back into relatively undisturbed equilibrium states after unequal mass mergers and fly-bys. About 1 Gyr after the first encounter, the RCs show no severe distortions anymore. These results are consistent with previous theoretical and observational studies. As an illustration of our results, we compare our simulated velocity fields and direct images with rotation curves from VLT/FORS spectroscopy and ACS images of a cluster at z=0.53 and find remarkable similarities.Comment: 13 pages, 14 figures, accepted for publication in A&A, some improvements and changes, main conclusions are unaffecte

The effects of ram-pressure stripping on the internal kinematics of simulated spiral galaxies

We investigate the influence of ram-pressure stripping on the internal gas kinematics of simulated spiral galaxies. Additional emphasis is put on the question of how the resulting distortions of the gaseous disc are visible in the rotation curve and/or the full 2D velocity field of galaxies at different redshifts. A Milky-Way type disc galaxy is modelled in combined N-body/hydrodynamic simulations with prescriptions for cooling, star formation, stellar feedback, and galactic winds. This model galaxy moves through a constant density and temperature gas, which has parameters similar to the intra-cluster medium (ICM). Rotation curves (RCs) and 2D velocity fields of the gas are extracted from these simulations in a way that follows the procedure applied to observations of distant, small, and faint galaxies as closely as possible. We find that the appearance of distortions of the gaseous disc due to ram-pressure stripping depends on the direction of the acting ram pressure. In the case of face-on ram pressure, the distortions mainly appear in the outer parts of the galaxy in a very symmetric way. In contrast, in the case of edge-on ram pressure we find stronger distortions. The 2D velocity field also shows signatures of the interaction in the inner part of the disc. At angles smaller than 45 degrees between the ICM wind direction and the disc, the velocity field asymmetry increases significantly compared to larger angles. Compared to distortions caused by tidal interactions, the effects of ram-pressure stripping on the velocity field are relatively low in all cases and difficult to observe at intermediate redshift in seeing-limited observations. (abridged)Comment: 9 pages, 11 figures, accepted for publication in A&

2D velocity fields of simulated interacting disc galaxies

We investigate distortions in the velocity fields of disc galaxies and their use to reveal the dynamical state of interacting galaxies at different redshift. For that purpose, we model disc galaxies in combined N-body/hydrodynamic simulations. 2D velocity fields of the gas are extracted from these simulations which we place at different redshifts from z=0 to z=1 to investigate resolution effects on the properties of the velocity field. To quantify the structure of the velocity field we also perform a kinemetry analysis. If the galaxy is undisturbed we find that the rotation curve extracted from the 2D field agrees well with long-slit rotation curves. This is not true for interacting systems, as the kinematic axis is not well defined and does in general not coincide with the photometric axis of the system. For large (Milky way type) galaxies we find that distortions are still visible at intermediate redshifts but partly smeared out. Thus a careful analysis of the velocity field is necessary before using it for a Tully-Fisher study. For small galaxies (disc scale length ~2 kpc) even strong distortions are not visible in the velocity field at z~0.5 with currently available angular resolution. Therefore we conclude that current distant Tully-Fisher studies cannot give reliable results for low-mass systems. Additionally to these studies we confirm the power of near-infrared integral field spectrometers in combination with adaptive optics (such as SINFONI) to study velocity fields of galaxies at high redshift (z~2).Comment: 12 pages, 18 figures, accepted for publication in A&A, high resolution version can be found at http://astro.uibk.ac.at/~thomas/kronberger.pd

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 ($10^{-28}$ g/cm$^3$), hot (3 keV $\approx 3.6\times10^7$K) and has a relative velocity of 1000 km/s, 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 three 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 $\sim50$% of the total gas of the colliding galaxies after 500 Myr the galaxies start to feel the ram pressure. Nearly $\sim10-15$ 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. (abrigded)Comment: 11 pages, 12 figures, accepted for publication in MNRA

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

(Abridged) We study the impact of cluster environment on the evolution of spiral galaxies by examining their structure and kinematics. Rather than two-dimensional rotation curves, we observe complete velocity fields by placing three adjacent and parallel FORS2 MXU slits on each object, yielding several emission and absorption lines. The gas velocity fields are reconstructed and decomposed into circular rotation and irregular motions using kinemetry. To quantify irregularities in the gas kinematics, we define three parameters: sigma_{PA} (standard deviation of the kinematic position angle), Delta phi (the average misalignment between kinematic and photometric position angles) and k_{3,5} (squared sum of the higher order Fourier terms). Using local, undistorted galaxies from SINGS, these can be used to establish the regularity of the gas velocity fields. Here we present the analysis of 22 distant galaxies in the MS0451.6-0305 field with 11 members at z=0.54. In this sample we find both field (4 out of 8) and cluster (3 out of 4) galaxies with velocity fields that are both irregular and asymmetric. We show that these fractions are underestimates of the actual number of galaxies with irregular velocity fields. The values of the (ir)regularity parameters for cluster galaxies are not very different from those of the field galaxies, implying that there are isolated field galaxies that are as distorted as the cluster members. None of the deviations in our small sample correlate with photometric/structural properties like luminosity or disk scale length in a significant way. Our 3D-spectroscopic method successfully maps the velocity field of distant galaxies, enabling the importance and efficiency of cluster specific interactions to be assessed quantitatively.Comment: accepted for publication in A&A, high resolution version available at http://www.astro.rug.nl/~kutdemir/papers

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

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 mech- anisms 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 pro- cesses, 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 artifcial 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 > 3E7 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.Comment: 7 pages, 9 figures, accepted for publication in A&

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 z>2 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 z<2 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.Comment: 11 pages, 13 figures, accepted for publication in A&A, high resolution version can be found at <http://astro.uibk.ac.at/~wolfgang/kapferer.pdf