1,917 research outputs found
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&
Inhomogeneous Metal Distribution in the Intra-Cluster Medium
The hot gas that fills the space between galaxies in clusters is rich in
metals. In their large potential wells, galaxy clusters accumulate metals over
the whole cluster history and hence they retain important information on
cluster formation and evolution. We use a sample of 5 cool core clusters to
study the distribution of metals in the ICM. We investigate whether the X-ray
observations yield good estimates for the metal mass and whether the heavy
elements abundances are consistent with a certain relative fraction of SN Ia to
SNCC. We derive detailed metallicity maps of the clusters from XMM - Newton
observations and we use them as a measure for the metal mass in the ICM. We
determine radial profiles for several elements and using population synthesis
and chemical enrichment models, we study the agreement between the measured
abundances and the theoretical yields. We show that even in relaxed clusters
the distribution of metals show a lot of inhomogeneities. Using metal maps
usually gives a metal mass 10-30% higher than the metal mass computed using a
single extraction region, hence it is expected that most previous metal mass
determination have underestimated metal mass. The abundance ratio of
{\alpha}-elements to Fe, even in the central parts of clusters, are consistent
with an enrichment due to the combination of SN Ia and SNCC
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Metal enrichment of the intra-cluster medium by thermally and cosmic-ray driven galactic winds
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. 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. We find that galactic
winds alone cannot account for the observed metallicity of the ICM. At redshift
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.Comment: 9 pages, 6 figures, accepted by A&
The effect of ram pressure on the star formation, mass distribution and morphology of galaxies
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, H and HI wavelength for different ram-pressure
scenarios are presented. 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 to 1000 km/s in
different surrounding gas densities in the range from to
g/cm. The temperature of the surrounding gas was
initially K. The star formation of a galaxy is enhanced by more
than a magnitude in the simulation with a high ram-pressure (
dyn/cm) 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. (Abridged)Comment: 19 pages, 25 figures, A&A accepted, high resolution version can be
found at http://astro.uibk.ac.at/~wolfgang/kapferer_rps_galaxies.pd
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&
Galaxies undergoing ram-pressure stripping: the influence of the bulge on morphology and star formation rate
We investigate the influence of stellar bulges on the star formation and
morphology of disc galaxies that suffer from ram pressure. Several tree-SPH
(smoothed particle hydrodynamics) simulations have been carried out to study
the dependence of the star formation rate on the mass and size of a stellar
bulge. In addition, different strengths of ram pressure and different
alignments of the disc with respect to the intra-cluster medium (ICM) are
applied. As claimed in previous works, when ram pressure is acting on a galaxy,
the star formation rate (SFR) is enhanced and rises up to four times with
increasing ICM density compared to galaxies that evolve in isolation. However,
a bulge suppresses the SFR when the same ram pressure is applied. Consequently,
fewer new stars are formed because the SFR can be lowered by up to 2 M_sun/yr.
Furthermore, the denser the surrounding gas, the more inter-stellar medium
(ISM) is stripped. While at an ICM density of 10^-28 g/cm^3 about 30% of the
ISM is stripped, the galaxy is almost completely (more than 90%) stripped when
an ICM density of 10^-27 g/cm^3 is applied. But again, a bulge prevents the
stripping of the ISM and reduces the amount being stripped by up to 10%.
Thereby, fewer stars are formed in the wake if the galaxy contains a bulge. The
dependence of the SFR on the disc tilt angle is not very pronounced. Hereby a
slight trend of decreasing star formation with increasing inclination angle can
be determined. Furthermore, with increasing disc tilt angles, less gas is
stripped and therefore fewer stars are formed in the wake. Reducing the disc
gas mass fraction results in a lower SFR when the galaxies evolve in vacuum. On
the other hand, the enhancement of the SFR in case of acting ram pressure is
less pronounced with increasing gas mass fraction. Moreover, the fractional
amount of stripped gas does not depend on the gas mass fraction.Comment: 11 pages, 18 figure
On the influence of ram-pressure stripping on the star formation of simulated spiral galaxies
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 where the newly formed stars are located. The stripping radius
from the simulation is compared to analytical estimates. 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=3 keV ~3.6x10^7 K and rho=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. 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_sun. As 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 is in good agreement 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.Comment: 8 pages, 7 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
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
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