arXiv subjects

D. Breitschwerdt

Publications and source records attributed to D. Breitschwerdt.

31 records · Page 2Linked to original sources

arXiv2005

Simulations of galactic winds and starbursts in galaxy clusters

We present an investigation of the metal enrichment of the intra-cluster medium (ICM) by galactic winds and merger-driven starbursts. We use combined N-body/hydrodynamic simulations with a semi-numerical galaxy formation model. The mass loss by galactic winds is obtained by calculating transonic solutions of steady state outflows, driven by thermal, cosmic ray and MHD wave pressure. The inhomogeneities in the metal distribution caused by these processes are an ideal tool to reveal the dynamical state of a galaxy cluster. We present surface brightness, X-ray emission weighted temperature and metal maps of our model clusters as they would be observed by X-ray telescopes like XMM-Newton. We show that X-ray weighted metal maps distinguish between pre- or post-merger galaxy clusters by comparing the metallicity distribution with the galaxy-density distribution: pre-mergers have a metallicity gap between the subclusters, post-mergers a high metallicity between subclusters. We apply our approach to two observed galaxy clusters, Abell 3528 and Abell 3921, to show whether they are pre- or post-merging systems. The survival time of the inhomogeneities in the metallicity distribution found in our simulations is up to several Gyr. We show that galactic winds and merger-driven starbursts enrich the ICM very efficiently after z=1 in the central (~ 3 Mpc radius) region of a galaxy cluster.

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arXiv2005

The multi-phase gaseous halos of star forming late-type galaxies - I. XMM-Newton observations of the Hot Ionized Medium

This study presents first results from an X-ray mini-survey carried out with XMM-Newton to investigate the diffuse Hot Ionized Medium in the halos of nine nearby star-forming edge-on spiral galaxies. Diffuse gaseous X-ray halos are detected in eight of our targets, covering a wide range of star formation rates from quiescent to starburst cases. For four edge-on spiral galaxies, namely NGC3044, NGC3221, NGC4634, and NGC5775, we present the first published high resolution/sensitivity detections of extended soft X-ray halos. EPIC X-ray contour maps overlaid onto Halpha imaging data reveals that in all cases the presence of X-ray halos is correlated with extraplanar Diffuse Ionized Gas. Moreover, these halos are also associated with non-thermal cosmic ray halos, as evidenced by radio continuum observations. Supplemental UV-data obtained with the OM-telescope at 210nm show Diffuse Ionized Gas to be well associated with UV emission originating in the underlying disk. Beside NGC891, NGC4634 is the second non-starburst galaxy with a diffuse soft X-ray halo (|z|<4kpc). In case of NGC3877, for which we also present the first high resolution X-ray imaging data, no halo emission is detectable. EPIC pn spectra (0.3-12keV) of the diffuse X-ray emission are extracted at different offset positions from the disk, giving evidence to a significant decrease of gas temperatures, electron densities, and gas masses with increasing distance to the plane. A comparison between dynamical and radiative cooling time scales implies that the outflow in all targets is likely to be sustained. We find very strong indications that spatially correlated multi-phase gaseous halos are created by star forming activity in the disk plane.

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arXiv2005

Stephan's Quintet with XMM-Newton

The prototype compact group known as Stephan's Quintet (SQ) was observed with XMM-Newton in order to complement the excellent resolution of Chandra with high sensitivity to extended emission. SQ is a dynamic environment whose main effect, at both X-ray and optical wavelengths, appears to be ISM stripping. This is manifested by: 1) secular evolution of morphological types towards earlier types and 2) growth of diffuse emission. Virtually all cold, warm and hot gas in SQ is found outside of the member galaxies. XMM-Newton offers the opportunity to study the hot gas with unprecedented sensitivity. We find two main components: 1) extended high surface brightness emission from shocked gas associated with an ongoing collision and 2) even more extended and unrelaxed diffuse emission that follows the stripped stellar envelope of the group.

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arXiv2005

Metal Enrichment Processes in the Intra-Cluster Medium

We present numerical simulations of galaxy clusters which include interaction processes between the galaxies and the intra-cluster gas. The considered interaction processes are galactic winds and ram-pressure stripping, which both transfer metal-enriched interstellar medium into the intra-cluster gas and hence increase its metallicity. We investigate the efficiency and time evolution of the interaction processes by simulated metallicity maps, which are directly comparable to those obtained from X-ray observations. We find that ram-pressure stripping is more efficient than quiet (i.e. non-starburst driven) galactic winds in the redshift interval between 1 and 0. The expelled metals are not mixed immediately with the intra-cluster gas, but inhomogeneities are visible in the metallicity maps. Even stripes of higher metallicity that a single galaxy has left behind can be seen. The spatial distribution of the metals transported by ram-pressure stripping and by galactic winds are very different for massive clusters: the former process yields a centrally concentrated metal distribution while the latter results in an extended metal distribution.

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arXiv2005

Keynote Lecture: Galactic and Extragalactic Bubbles

The observational and theoretical state of Galactic and extragalactic bubbles are reviewed. Observations of superbubbles are discussed, with some emphasis on nearby bubbles such as the Local Bubble (LB) and the Loop I superbubble (LI). Analytical bubble theory is revisited, and similarity solutions, including the time-dependent energy input by supernova explosions according to a Galactic initial mass function (IMF), are studied. Since the agreement with observations is not convincing in case of the LB, we present high resolution 3D AMR simulations of the LB and LI in an inhomogeneous background medium. It is demonstrated that both the morphology and recently published FUSE data on OVI absorption line column densities can be well understood, if the LB is the result of about 20 supernova explosions from a moving group, and the LB age is about 14.7 Myrs.

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arXiv2004

Metal Enrichment and Energetics of Galactic Winds in Galaxy Clusters

We investigate efficiency and time dependence of metal enrichment processes in the Intra-Cluster Medium (ICM). In this presentation we concentrate on the effects of galactic winds. The mass loss rates due to galactic winds are calculated with a special algorithm, which takes into account cosmic rays and magnetic fields. This algorithm is embedded in a combined N-body/hydrodynamic code which calculates the dynamics and evolution of a cluster. We present mass loss rates depending on galaxy properties like type, mass, gas mass fraction and the surrounding ICM. In addition we show metallicity maps as they would be observed with X-ray telescopes.

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arXiv2003

Does the interstellar magnetic field follow the Chandrasekhar-Fermi law?

We carried out 1.25 pc resolution MHD simulations of the ISM -- including the large scale galactic fountain -- by fully tracking the time-dependent evolution of the magnetic field and the formation of shock compressed regions in a supernova-driven ISM. The simulations show that large scale gas streams emerge, driven by SN explosions, which are responsible for the formation and destruction of shocked compressed layers with lifetimes up to some 15 Myr. The T\leq 10^{3} K gas is distributed in filaments which tend to show a preferred orientation due to the anisotropy of the flow induced by the galactic magnetic field. The simulations also show that the magnetic field has a high variability, it is largely uncorrelated with the density and it is driven by inertial motions. The latter is consistent with the fact that ram pressure dominates the flow for 10^{2} 10^{6} K thermal pressure dominates, while for T\leq 10^{2} K (stable branch) magnetic pressure takes over.

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arXiv2003

MHD Simulations of the ISM: The Importance of the Galactic Magnetic Field on the ISM "Phases"

We have carried out 1.25 pc resolution MHD simulations of the ISM, on a Cartesian grid of $0 \leq (x,y) \leq 1$ kpc size in the galactic plane and $-10 \leq z \leq 10$ kpc into the halo, thus being able to fully trace the time-dependent evolution of the galactic fountain. The simulations show that large scale gas streams emerge, driven by SN explosions, which are responsible for the formation and destruction of shocked compressed layers. The shocked gas can have densities as high as 800 cm$^{-3}$ and lifetimes up to 15 Myr. The cold gas is distributed into filaments which tend to show a preferred orientation due to the anisotropy of the flow induced by the galactic magnetic field. Ram pressure dominates the flow in the unstable branch $10^{2}<$T$\leq 10^{3.9}$ K, while for T$\leq 100$ K (stable branch) magnetic pressure takes over. Near supernovae thermal and ram pressures determine the dynamics of the flow. Up to 80% of the mass in the disk is concentrated in the thermally unstable regime $10^{2}<$T$\leq 10^{3.9}$ K with $\sim30%$ of the disk mass enclosed in the T$\leq 10^{3}$ K gas. The hot gas in contrast is controlled by the thermal pressure, since magnetic field lines are swept towards the dense compressed walls.

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arXiv2003

From Large to Small Scales: Global Models of the ISM

We review large scale modelling of the ISM with emphasis on the importance to include the disk-halo-disk duty cycle and to use a dynamical refinement of the grid (in regions where steep variations of density and pressure occur) for a realistic modelling of the ISM. We also discuss the necessity of convergence of the simulation results by comparing 0.625, 1.25 and 2.5 pc resolution simulations and show that a minimum grid resolution of 1.25 pc is required for quantitatively reliable results, as there is a rapid convergence for Delta x \leq 1.1 pc.

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arXiv2003

Stephan's Quintet: The X-ray Anatomy of a Multiple Galaxy Collision

Chandra observations of the compact galaxy group known as Stephan's Quintet (SQ) are presented. The major morphological features that were discovered with the ROSAT HRI are now imaged with higher resolution and S/N. The large scale shock (1.5', ~40kpc if at 85 Mpc) is resolved into a narrow NS feature embedded in more extended diffuse emission (D>=3'). The NS structure is somewhat clumpy, more sharply bounded on the W side and prominent only in the soft band (energies below ~2 keV). Its observational properties are best explained as a shock produced by a high velocity encounter between NGC7318b, a ``new intruder'', and the intergalactic medium in SQ. The shock conditions near the high speed intruder suggest that a bow shock is propagating into a pre-existing HI cloud and heating the gas to a temperature of ~0.5 keV. The low temperature in the shock is a problem unless we postulate an oblique shock. One member, NGC7319, hosts a Seyfert 2 nucleus, with an intrinsic luminosity Lx=10^43 erg/s, embedded in a region of more diffuse emission with 10'' radius extent. The nuclear spectrum can be modeled with a strongly absorbed power-law typical of this class of sources. Several additional compact sources are detected including three in foreground NGC7320. Some of these sources are very luminous and could be related to the ultraluminous X-ray sources found in nearby galaxies.

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arXiv2002

The origin of the young stellar population in the solar neighborhood - a link to the formation of the Local Bubble?

We have analyzed the trajectories of moving stellar groups in the solar neighborhood in an attempt to estimate the number of supernova explosions in our local environment during the past 20 million years. Using Hipparcos stellar distances and the results of kinematical analyses by Asiain et al. (1999a) on the Pleiades moving groups, we are able to show that subgroup B1, consisting of early type B stars up to 10 Msun, but lacking more massive objects, has passed through the local interstellar medium within less than 100 pc. Comparing the stellar content of B1 with the initial mass function derived from the analysis of galactic OB associations, we estimate the number of supernova explosions and find that about 20 supernovae must have occurred during the past ~ 10 - 20 million years, which is suggested to be the age of the Local Bubble; the age of the star cluster is about ~ 20 - 30 million years. For the first time, this provides strong evidence that the Local Bubble must have been created and shaped by multi-supernova explosions and presumably been reheated more than 1 million years ago, consistent with recent findings of an excess of 60Fe in a deep ocean ferromanganese crust. Calculating similarity solutions of an expanding superbubble for time-dependent energy input, we show that the number of explosions is sufficient to explain the size of the Local Bubble. The present energy input rate is about $\dot E_{SN}$ ~ 5 x 10^36 erg/s, in good agreement with the estimated local soft X-ray photon output rate. It seems plausible that the origin of the Local Bubble is also linked to the formation of the Gould Belt, which originated about 30-60 Myrs ago.

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arXiv2002

The gradient of diffuse gamma-ray emission in the Galaxy

We show that the well-known discrepancy between the radial dependence of the Galactic cosmic ray (CR) nucleon distribution, as inferred most recently from EGRET observations of diffuse gamma-rays above 100 MeV, and of the most likely CR source distribution (supernova remnants, pulsars) can be explained purely by PROPAGATION effects. Contrary to previous claims, we demonstrate that this is possible, if the dynamical coupling between the escaping CRs and thermal plasma is taken into account, and thus a self-consistent GALACTIC WIND calculation is carried out. Given a dependence of the CR source distribution on Galactocentric radius, r, our numerical wind solutions show that the CR outflow velocity, V(r,z) depends both on r, and on vertical distance, z, at reference level z_C. The latter is defined as the transition boundary from diffusion to advection dominated CR transport and is therefore also a function of r. In fact, the CR escape time averaged over particle energies decreases with increasing CR source strength. Such an increase is counteracted by a reduced average CR residence time in the gas disk. Therfore pronounced peaks in the radial source distribution result in mild radial gamma-ray gradients at GeV energies, as it has been observed. This effect is enhanced by anisotropic diffusion, assuming different radial and vertical diffusion coefficients. We have calculated 2D analytic solutions of the stationary diffusion-advection equation, including anisotropic diffusion, for a given CR source distribution and a realistic outflow velocity field V(r,z), inferred from self-consistent numerical Galactic Wind simulations. At TeV energies the gamma-rays from the sources are expected to dominate the observed "diffuse" flux from the disk. Its observation should allow an empirical test of the theory presented.

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arXiv1999

The Diffuse Galactic Gamma-Ray Gradient

One of the unsolved problems in cosmic ray (CR) physics is the small radial gradient of the gamma-ray intensity compared to the inferred CR source distribution in the Galactic disk. In diffusive CR propagation models the most natural explanation is very efficient spatial mixing due to MHD turbulence in the interstellar medium. However, even in the most favorable case of a very large diffusive CR halo the gamma-ray gradient is still larger than observed. In our view such a small gradient could be the result of strong advection by a Galactic wind. We show that a small gamma-ray gradient can be obtained, if the diffusion region does NOT extend far above the Galactic plane. Important ingredients of our model are: (i) anisotropic CR diffusion, (ii) strong radial and vertical gradients of the advection velocity (due to faster winds above higher CR source density regions).

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