25,140 research outputs found
Constraints on turbulent velocity broadening for a sample of clusters, groups and elliptical galaxies using XMM-Newton
Using the width of emission lines in XMM-Newton Reflection Grating
Spectrometer spectra, we place direct constraints on the turbulent velocities
of the X-ray emitting medium in the cores of 62 galaxy clusters, groups and
elliptical galaxies. We find five objects where we can place an upper limit on
the line-of-sight broadening of 500 km/s (90 per cent confidence level), using
a single thermal component model. Two other objects are lower than this limit
when two thermal components are used. Half of the objects examined have an
upper limit on the velocity broadening of less than 700 km/s. To look for
objects which have significant turbulent broadening, we use Chandra spectral
maps to compute the expected broadening caused by the spatial extent of the
source. Comparing these with our observed results, we find that Klemola 44 has
extra broadening at the level of 1500 km/s. RX J1347.5-1145 shows weak evidence
for turbulent velocities at 800 km/s. In addition we obtain limits on
turbulence for Zw3146, Abell 496, Abell 1795, Abell 2204 and HCG 62 of less
than 200 km/s. After subtraction of the spatial contribution and including a 50
km/s systematic uncertainty, we find at least 15 sources with less than 20 per
cent of the thermal energy density in turbulence.Comment: 17 pages, 17 figures, accepted by MNRAS. Includes minor edits to
proo
Searching for the missing iron in the core of the Centaurus cluster
We re-analyse a combined 198 ks Chandra observation of NGC4696, the brightest
galaxy of the Centaurus cluster. We extract temperature and metallicity
profiles from the data, and we confirm the presence of a sharp drop in iron
abundance, from ~1.8 Zsolar to ~0.4 Zsolar, within the central 5 kpc of the
cluster. We estimate that this abundance drop corresponds to a total "missing"
iron mass of 1.4e06 Msolar. We propose that part of this missing iron is locked
up in cool (~19 K) far-IR emitting dust, as found by Spitzer and Herschel
observations. This can occur if the iron injected by stellar mass loss in the
central region is in grains, which remain in that form as the injected dusty
cold gas mixes and joins the cold dusty filamentary nebula observed within the
same region. The bubbling feedback process observed in the cluster core then
drags filaments outward and dumps them at 10-20 kpc radius, where the
metallicity is high.Comment: 8 pages, accepted for publication in MNRA
Resolving the virial discrepancy in clusters of galaxies with modified Newtonian dynamics
A sample of 197 X-ray emitting clusters of galaxies is considered in the
context of Milgrom's modified Newtonian dynamics (MOND). It is shown that the
gas mass, extrapolated via an assumed model to a fixed radius of 3 Mpc,
is correlated with the gas temperature as predicted by MOND (). The observed temperatures are generally consistent with the inferred
mass of hot gas; no substantial quantity of additional unseen matter is
required in the context of MOND. However, modified dynamics cannot resolve the
strong lensing discrepancy in those clusters where this phenomenon occurs. The
prediction is that additional baryonic matter may be detected in the central
regions of rich clusters.Comment: Submitted to A&A, 4 pages, 3 figures, A&A macro
Elastocapillary folding of three dimensional micro-structures using water pumped through the wafer via a silicon nitride tube
In this paper we present the first investigation of a batch method for folding of threedimensional micrometer-sized silicon nitride structures by capillary forces. Silicon nitride tubes have been designed and fabricated using DRIE at the center of the planar origami patterns of the structures. Water is brought to the structures by pumping the liquid through the wafer via those tubes. Isolated micro-structures were successfully folded using this method. The potential of this technique for batch self-assembly is discussed
A volume-limited sample of X-ray galaxy groups and clusters - II. X-ray cavity dynamics
We present the results of our study of a volume-limited sample (z <= 0.071)
of 101 X-ray galaxy groups and clusters, in which we explore the X-ray cavity
energetics. Out of the 101 sources in our parent sample, X-ray cavities are
found in 30 of them, all of which have a central cooling time of less than3
Gyr. New X-ray cavities are detected in three sources. We focus on the subset
of sources that have a central cooling time of less than 3 Gyr, whose active
galactic nucleus (AGN) duty cycle is approximately 61 percent (30/49). This
rises to over 80 percent for a central cooling time of less than 0.5 Gyr. When
projection effects and central radio source detection rates are considered, the
actual duty cycle is probably much higher. In addition, we show that data
quality strongly affects the detection rates of X-ray cavities. After
calculating the cooling luminosity and cavity powers of each source with
cavities, it is evident that the bubbling process induced by the central AGN
has to be, on average, continuous, to offset cooling. We find that the radius
of the cavities, r, loosely depends on the ambient gas temperature as T^0.5,
above about 1.5 keV, with much more scatter below that temperature. Finally, we
show that, at a given location in a group or cluster, larger bubbles travel
faster than smaller ones. This means that the bubbles seen at larger distances
from cluster cores could be the result of the merging of several smaller
bubbles, produced in separate AGN cycles.Comment: Accepted for publication in MNRAS; 26 pages (including 10 pages of
images), 8 figures, 2 tables. Higher resolution images will be available as
online materia
BOOMERanG Data Suggest a Purely Baryonic Universe
The amplitudes of peaks in the angular power spectrum of anisotropies in the
microwave background radiation depend on the mass content of the universe. The
second peak should be prominent when cold dark matter is dominant, but is
depressed when baryons dominate. Recent microwave background data are
consistent with a purely baryonic universe with Omega(matter) = Omega(baryon) ~
0.03 and Omega(Lambda) ~ 1.Comment: 10 pages AASTeX with 1 color postscript figure. Accepted for
publication in ApJ Letters. And yes, the prediction was in the literature
before the dat
Testing a double AGN hypothesis for Mrk 273
The ULIRG Mrk 273 contains two infrared nuclei, N and SW, separated by 1
arcsec. A Chandra observation has identified the SW nucleus as an absorbed
X-ray source with nH ~4e23 cm-2 but also hinted at the possible presence of a
Compton thick AGN in the N nucleus, where a black hole of 10^9 Msun is inferred
from the ionized gas kinematics. The intrinsic X-ray spectral slope recently
measured by NuSTAR is unusually hard (photon index of ~1.3) for a Seyfert
nucleus, for which we seek an alternative explanation. We hypothesise a
strongly absorbed X-ray source in N, of which X-ray emission rises steeply
above 10 keV, in addition to the known X-ray source in SW, and test it against
the NuSTAR data, assuming the standard spectral slope (photon index of 1.9).
This double X-ray source model gives a good explanation of the hard continuum
spectrum, the deep Fe K absorption edge, and the strong Fe K line observed in
this ULIRG, without invoking the unusual spectral slope required for a single
source interpretation. The putative X-ray source in N is found to be absorbed
by nH = 1.4(+0.7/-0.4)e24 cm-2. The estimated 2-10 keV luminosity of the N
source is 1.3e43 erg/s, about a factor of 2 larger than that of SW during the
NuSTAR observation. Uncorrelated variability above and below 10 keV between the
Suzaku and NuSTAR observations appears to support the double source
interpretation. Variability in spectral hardness and Fe K line flux between the
previous X-ray observations is also consistent with this picture.Comment: 6 pages, 5 figures, Accepted for publication in A&
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