53 research outputs found
Elemental Abundances in the X-Ray Gas of Early-Type Galaxies with XMM and Chandra Observations
The source of hot gas in elliptical galaxies is thought to be due to stellar
mass loss, with contributions from supernova events and possibly from infall
from a surrounding environment. This picture predicts supersolar values for the
metallicity of the gas toward the inner part of the galaxy, which can be tested
by measuring the gas phase abundances. We use high-quality data for 10 nearby
early-type galaxy from XMM-Newton, featuring both the EPIC and the Reflection
Grating Spectrometer, where the strongest emission lines are detected with
little blending; some Chandra data are also used. We find excellent consistency
in the elemental abundances between the different XMM instruments and good
consistency with Chandra. Differences in abundances with aperture size and
model complexity are examined, but large differences rarely occur. For a
two-temperature thermal model plus a point source contribution, the median Fe
and O abundances are 0.86 and 0.44 of the Solar value, while Si and Mg
abundances are similar to that for Fe. This is similar to stellar abundances
for these galaxies but supernovae were expected to enhance the gas phase
abundances considerably, which is not observed.Comment: 35 pages, 10 figures, accepted for publication in Astrophysical
Journa
X-ray Isophotes in a Rapidly Rotating Elliptical Galaxy: Evidence of Inflowing Gas
We describe two-dimensional gasdynamical computations of the X-ray emitting
gas in the rotating elliptical galaxy NGC 4649 that indicate an inflow of about
one solar mass per year at every radius. Such a large instantaneous inflow
cannot have persisted over a Hubble time. The central constant-entropy
temperature peak recently observed in the innermost 150 parsecs is explained by
compressive heating as gas flows toward the central massive black hole. Since
the cooling time of this gas is only a few million years, NGC 4649 provides the
most acutely concentrated known example of the cooling flow problem in which
the time-integrated apparent mass that has flowed into the galactic core
exceeds the total mass observed there. This paradox can be resolved by
intermittent outflows of energy or mass driven by accretion energy released
near the black hole. Inflowing gas is also required at intermediate kpc radii
to explain the ellipticity of X-ray isophotes due to spin-up by mass ejected by
stars that rotate with the galaxy and to explain local density and temperature
profiles. We provide evidence that many luminous elliptical galaxies undergo
similar inflow spin-up. A small turbulent viscosity is required in NGC 4649 to
avoid forming large X-ray luminous disks that are not observed, but the
turbulent pressure is small and does not interfere with mass determinations
that assume hydrostatic equilibrium.Comment: 21 pages, 9 figures, accepted for publication by Ap
Simulating the Hot X-ray Emitting Gas in Elliptical Galaxies
We study the chemo-dynamical evolution of elliptical galaxies and their hot
X-ray emitting gas using high-resolution cosmological simulations. Our Tree
N-body/SPH code includes a self-consistent treatment of radiative cooling, star
formation, supernovae feedback, and chemical enrichment. We present a series of
LCDM cosmological simulations which trace the spatial and temporal evolution of
heavy element abundance patterns in both the stellar and gas components of
galaxies. X-ray spectra of the hot gas are constructed via the use of the
vmekal plasma model, and analysed using XSPEC with the XMM EPN response
function. Simulation end-products are quantitatively compared with the
observational data in both the X-ray and optical regime. We find that radiative
cooling is important to interpret the observed X-ray luminosity, temperature,
and metallicity of the interstellar medium of elliptical galaxies. However,
this cooled gas also leads to excessive star formation at low redshift, and
therefore results in underlying galactic stellar populations which are too blue
with respect to observations.Comment: 6 pages, 3 figures, to appear in the proceedings of "The IGM/Galaxy
Connection - The Distribution of Baryons at z=0", ed. M. Putman & J.
Rosenberg; High resolution version is available at
http://astronomy.swin.edu.au/staff/dkawata/research/papers.htm
An XMM-Newton study of the RGH 80 galaxy group
We present an X-ray study of the galaxy group RGH 80, observed by XMM-Newton.
The X-ray emission of the gas is detected out to ~ 462h^{-1}_{50} kpc,
corresponding to ~ 0.45 r_{200}. The group is relatively gas rich and luminous
with respect to its temperature of 1.01 +/- 0.01 keV. Using the deprojected
spectral analysis, we find that the temperature peaks at ~ 1.3 keV around
0.11r_{200}, and then decreases inwards to 0.83 keV at the center and outwards
to ~ 70% of the peak value at large radii. Within the central ~ 60 kpc of the
group where the gas cooling time is less than the Hubble time, two-temperature
model with temperatures of 0.82 and 1.51 keV and the Galactic absorption gives
the best fit of the spectra, with ~ 20% volume occupied by the cool component.
We also derive the gas entropy distribution, which is consistent with the
prediction of cooling and/or internal heating models. Furthermore, the
abundances of O, Mg, Si, S, and Fe decrease monotonically with radius. With the
observed abundance ratio pattern, we estimate that ~ 85% or ~ 72% of the iron
mass is contributed by SN Ia, depending on the adopted SN II models.Comment: 14 pages, 9 figures, accepted for publication in A&
Abundance ratios in the hot ISM of elliptical galaxies
To constrain the recipes put forth to solve the theoretical Fe discrepancy in
the hot interstellar medium of elliptical galaxies and at the same time explain
the [alpha/Fe] ratios. In order to do so we use the latest theoretical
nucleosynthetic yields, we incorporate the dust, we explore differing SNIa
progenitor scenarios by means of a self-consistent chemical evolution model
which reproduces the properties of the stellar populations in elliptical
galaxies. Models with Fe-only dust and/or a lower effective SNIa rate achieve a
better agreement with the observed Fe abundance. However, a suitable
modification to the SNIa yield with respect to the standard W7 model is needed
to fully match the abundance ratio pattern. The 2D explosion model C-DDT by
Maeda et al. (2010) is a promising candidate for reproducing the [Fe/H] and the
[alpha/Fe] ratios. (A&A format)Comment: 11 pages, 4 figures, to appear on A&
Reconciling stellar dynamical and hydrostatic X-ray mass measurements of an elliptical galaxy with gas rotation, turbulence and magnetic fields
Recent hydrostatic X-ray studies of the hot interstellar medium (ISM) in
early-type galaxies underestimate the gravitating mass as compared to stellar
dynamics, implying modest, but significant deviations from exact hydrostatic
equilibrium. We present a method for combining X-ray measurements and stellar
dynamical constraints in the context of Bayesian statistics that allows the
radial distribution of the implied nonthermal pressure or bulk motions in the
hot ISM to be constrained. We demonstrate the accuracy of the method with
hydrodynamical simulations tailored to produce a realistic galaxy model.
Applying the method to the nearby elliptical galaxy NGC4649, we find a
significant but subdominant nonthermal pressure fraction (0.27+/-0.06) in the
central (<5 kpc) part of the galaxy, similar to the level of deviations from
hydrostatic equilibrium expected in galaxy clusters. Plausible sources of
systematic error, if important, may reduce this fraction. This would imply >360
km/s random turbulence or a magnetic field B=(39+/-6)(n_e/0.1
cm^{-3})^{0.59+/-0.09} muG, whereas gas rotation alone is unlikely to explain
the detailed nonthermal profile. Future observations with Astro-H will allow
turbulence or gas rotation at this level to be detected.Comment: 14 pages, 8 figures, 1 table. Accepted by Monthly Notices of the
Royal Astronomical Society. Minor changes to match accepted versio
An XMM-Newton observation of the galaxy group MKW 4
We present an X-ray study of the galaxy group or poor cluster MKW 4. Working
with XMM data we examine the distribution and properties of the hot gas which
makes up the group halo. The inner halo shows some signs of structure, with
circular or elliptical beta models providing a poor fit to the surface
brightness profile. This may be evidence of large scale motion in the inner
halo, but we do not find evidence of sharp fronts or edges in the emission. The
temperature of the halo declines in the core, with deprojected spectral fits
showing a central temperature of ~1.3 keV compared to ~3 keV at 100 kpc. In the
central ~30 kpc of the group multi-temperature spectral models are required to
fit the data, but they indicate a lack of gas at low temperatures. Steady state
cooling flow models provide poor fits to the inner regions of the group and the
estimated cooling time of the gas is long except within the central dominant
galaxy, NGC 4073. Abundance profiles show a sharp increase in the core of the
group, with mean abundance rising by a factor of two in the centre of NGC 4073.
Fitting individual elements shows the same trend, with high values of Fe, Si
and S in the core. We estimate that ~50% of the Fe in the central 40 kpc was
injected by SNIa, in agreement with previous ASCA studies. Using our best
fitting surface brightness and temperature models, we calculate the mass, gas
fraction, entropy and mass-to-light ratio of the group. At 100 kpc (~0.1 virial
radii) the total mass and gas entropy of the system (~2x10^13 Msol and ~300 keV
cm^2) are quite comparable to those of other systems of similar temperature,
but the gas fraction is rather low (~1%). We conclude that MKW 4 is a fairly
relaxed group, which has developed a strong central temperature gradient but
not a large-scale cooling flow.Comment: 17 pages, 9 postscript figures, accepted for publication in MNRA
Two-Phase ICM in the Central Region of the Rich Cluster of Galaxies Abell 1795: A Joint Chandra, XMM-Newton, and Suzaku View
Based on a detailed analysis of the high-quality Chandra, XMM-Newton, and
Suzaku data of the X-ray bright cluster of galaxies Abell 1795, we report clear
evidence for a two-phase intracluster medium (ICM) structure, which consists of
a cool (with a temperature T = 2.0-2.2 keV) and a hot (T = 5.0-5.7 keV)
component that coexist and dominate the X-ray emission at least in the central
80 kpc. A third weak emission component (T = 0.8 keV) is also detected within
the innermost 144 kpc and is ascribed to a portion of inter-stellar medium
(ISM) of the cD galaxy. Deprojected spectral analysis reveals flat radial
temperature distributions for both the hot phase and cool phase components.
These results are consistent with the ASCA measurements reported in Xu et al.
(1998), and resemble the previous findings for the Centaurus cluster (e.g.,
Takahashi et al. 2009). By analyzing the emission measure ratio and gas metal
abundance maps created from the Chandra data, we find that the cool phase
component is more metal-enriched than the hot phase one in 50-100 kpc region,
which agrees with that found in M87 (Simionescu et al. 2008). The coexistence
of the cool phase and hot phase ICM cannot be realized by bubble uplifting from
active galactic nuclei (AGN) alone. Instead, the two-phase ICM properties are
better reconciled with a cD corona model (Makishima et al. 2001). (Abridged)Comment: 47 pages, 12 figures, accepted for publication in Ap
X-ray Spectroscopy of Cooling Clusters
We review the X-ray spectra of the cores of clusters of galaxies. Recent high
resolution X-ray spectroscopic observations have demonstrated a severe deficit
of emission at the lowest X-ray temperatures as compared to that expected from
simple radiative cooling models. The same observations have provided compelling
evidence that the gas in the cores is cooling below half the maximum
temperature. We review these results, discuss physical models of cooling
clusters, and describe the X-ray instrumentation and analysis techniques used
to make these observations. We discuss several viable mechanisms designed to
cancel or distort the expected process of X-ray cluster cooling.Comment: To appear in Physics Reports, 71 pages, 20 figure
The elemental abundances in the intracluster medium as observed with XMM-Newton
XMM-Newton observations of 19 galaxy clusters are used to measure the
elemental abundances and their spatial distributions in the intracluster
medium. The sample mainly consists of X-ray bright and relaxed clusters with a
cD galaxy. Along with detailed Si, S and Fe radial abundance distributions
within 300-700 kpc in radius, the O abundances are accurately derived in the
central region of the clusters. The Fe abundance maxima towards the cluster
center, possibly due to the metals from the cD galaxy,are spatially resolved.
The Si and S abundances also exhibit central increases in general, resulting in
uniform Fe-Si-S ratios within the cluster. In contrast, the O abundances are in
general uniform over the cluster. The mean O to Fe ratio within the cluster
core is sub-solar, while that of the cluster scale is larger than the solar
ratio. These measurements indicate that most of the Fe-Si-S and O in the
intracluster medium have different origins, presumably in supernovae Ia and II,
respectively. The obtained Fe and O mass are also used to discuss the past star
formation history in clusters.Comment: Accepted for publication in Astronomy and Astrophysic
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