28,241 research outputs found
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
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
The X-ray coronae of the two brightest galaxies in the Coma cluster
We use deep Chandra X-ray Observatory observations to examine the coronae of
the two brightest cluster galaxies in the Coma cluster of galaxies, NGC 4874
and NGC 4889. We find that NGC 4889 hosts a central depression in X-ray surface
brightness consistent with a cavity or pair of cavities of radius 0.6 kpc. If
the central cavity is associated with an AGN outburst and contains relativistic
material, its enthalpy should be around 5x10^55 erg. The implied heating power
of this cavity would be around an order of magnitude larger than the energy
lost by X-ray emission. It would be the smallest and youngest known cavity in a
brightest cluster galaxy and the lack of over pressuring implies heating is
still gentle. In contrast, NGC 4874 does not show any evidence for cavities,
although it hosts a well-known wide-angle-tail radio source which is visible
outside the region occupied by the X-ray corona. These two galaxies show that
AGN feedback can behave in varied ways in the same cluster environment.Comment: 11 pages, 11 figures, accepted by MNRA
Recommended from our members
Oxygen isotopic constraints on the origin and parent bodies of eucrites, howardites, and diogenites
Recommended from our members
Oxygen Isotopic Constraints on the Number and Origin of Basaltic Achondrite Parent Bodies
Our data show that HED meteorites have a homogeneous oxygen isotopic composition consistent with a magma ocean on Vesta. Ibitira, Asuka 881394, Pasamonte, and NWA 1240 probably come from separate parent asteroids
Migrant and minority community organisations: funding, sustainability and ways forward
MODA (Migrant Organisations’ Development Agency) and Middlesex University have been working together on a research project about funding and resources available to migrant and minority organisations in London. This reports presents some of its key findings.
The aim of the project was to gather information about the role of minority and migrant organisations, including details about the services they provide, the community needs they address, the financial and organizational challenges they face and the creative ways they are
finding to cope. The research also aimed to explore the effects of the current economic and political climate on the sector and the role played by second tier organisations and other networks
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