190 research outputs found
An optical and X-ray study of the fossil group RX J1340.6+4018
Fossil groups are systems with one single central elliptical galaxy and an
unusual lack of luminous galaxies in the inner regions. The standard
explanation for the formation of these systems suggests that the lack of bright
galaxies is due to galactic cannibalism. In this study we show the results of
an optical and X-ray analysis of RX J1340.6+4018, the prototype fossil group.
The data indicates that RX J1340.6+4018 is similar to clusters in almost every
sense, dynamical mass, X-ray luminosity, M/L and luminosity function, except
for the lack of L* galaxies.
There are claims in the literature that fossil systems have a lack of small
mass haloes, compared to predictions based on the LCDM scenario. The
observational data gathered on this and other fossil groups so far offer no
support to this idea.
Analysis of the SN Ia/SN II ejecta ratio in the inner and outer regions shows
a marginally significant central dominance of SN Ia material. This suggests
that either the merger which originated the central galaxy was dry or the group
has been formed at early epochs, although better data are needed to confirm
this result.Comment: Accepted by AJ; 14 pages, 6 figure
Dynamical analysis of the cluster pair: A3407 + A3408
We carried out a dynamical study of the galaxy cluster pair A3407 \& A3408
based on a spectroscopic survey obtained with the 4 meter Blanco telescope at
the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122
member galaxies brighter than . Our main goal is to probe the galaxy
dynamics in this field and verify if the sample constitutes a single galaxy
system or corresponds to an ongoing merging process. Statistical tests were
applied to clusters members showing that both the composite system A3407 +
A3408 as well as each individual cluster have Gaussian velocity distribution. A
velocity gradient of was identified around
the principal axis of the projected distribution of galaxies, indicating that
the global field may be rotating. Applying the KMM algorithm to the
distribution of galaxies we found that the solution with two clusters is better
than the single unit solution at the 99\% c.l. This is consistent with the
X-ray distribution around this field, which shows no common X-ray halo
involving A3407 and A3408. We also estimated virial masses and applied a
two-body model to probe the dynamics of the pair. The more likely scenario is
that in which the pair is gravitationally bound and probably experiences a
collapse phase, with the cluster cores crossing in less than 1
Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature,
and some signs of galaxy evolution in A3408 suggests a post-merger scenario,
with cores having crossed each other Gyr ago, as an
alternative solution.Comment: 17 pages, 12 figures, submitted to MNRAS, accepted 2016 May 9.
Received 2016 May 9; in original form 2016 April 1
Mapping small-scale temperature and abundance structures in the core of the Perseus cluster
We report further results from a 191 ks Chandra observation of the core of
the Perseus cluster, Abell 426. The emission-weighted temperature and abundance
structure is mapped detail. There are temperature variations down to ~1 kpc in
the brightest regions. Globally, the strongest X-ray surface brightness
features appear to be caused by temperature changes. Density and temperature
changes conspire to give approximate azimuthal balance in pressure showing that
the gas is in hydrostatic equilibrium. Si, S, Ar, Ca, Fe and Ni abundance
profiles rise inward from about 100 kpc, peaking at about 30-40 kpc. Most of
these abundances drop inwards of the peak, but Ne shows a central peak, all of
which may be explained by resonance scattering. There is no evidence for a
widespread additional cooler temperature component in the cluster with a
temperature greater than a factor of two from the local temperature. There is
however evidence for a widespread hard component which may be nonthermal. The
temperature and abundance of gas in the cluster is observed to be correlated in
a manner similar to that found between clusters.Comment: ~20 pages, colour, accepted by MNRAS. Updates include a more
extensive discussion of the hard component, reference corrections, and a few
other minor changes. A version with good figure quality is at
http://www-xray.ast.cam.ac.uk/papers/perdetail
Turbulence and the formation of filaments, loops and shock fronts in NGC 1275 in the Perseus Galaxy Cluster
NGC1275, the central galaxy in the Perseus cluster, is the host of gigantic
hot bipolar bubbles inflated by AGN jets observed in the radio as Perseus A. It
presents a spectacular -emitting nebulosity surrounding NGC1275,
with loops and filaments of gas extending to over 50 kpc. The origin of the
filaments is still unknown, but probably correlates with the mechanism
responsible for the giant buoyant bubbles. We present 2.5 and 3-dimensional MHD
simulations of the central region of the cluster in which turbulent energy,
possibly triggered by star formation and supernovae (SNe) explosions is
introduced. The simulations reveal that the turbulence injected by massive
stars could be responsible for the nearly isotropic distribution of filaments
and loops that drag magnetic fields upward as indicated by recent observations.
Weak shell-like shock fronts propagating into the ICM with velocities of
100-500 km/s are found, also resembling the observations. The isotropic outflow
momentum of the turbulence slows the infall of the intracluster medium, thus
limiting further starburst activity in NGC1275. As the turbulence is subsonic
over most of the simulated volume, the turbulent kinetic energy is not
efficiently converted into heat and additional heating is required to suppress
the cooling flow at the core of the cluster. Simulations combining the MHD
turbulence with the AGN outflow can reproduce the temperature radial profile
observed around NGC1275. While the AGN mechanism is the main heating source,
the supernovae are crucial to isotropize the energy distribution.Comment: accepted by ApJ Letter
Galaxy properties from J-PAS narrow-band photometry
We study the consistency of the physical properties of galaxies retrieved
from SED-fitting as a function of spectral resolution and signal-to-noise ratio
(SNR). Using a selection of physically motivated star formation histories, we
set up a control sample of mock galaxy spectra representing observations of the
local universe in high-resolution spectroscopy, and in 56 narrow-band and 5
broad-band photometry. We fit the SEDs at these spectral resolutions and
compute their corresponding the stellar mass, the mass- and luminosity-weighted
age and metallicity, and the dust extinction. We study the biases,
correlations, and degeneracies affecting the retrieved parameters and explore
the r\^ole of the spectral resolution and the SNR in regulating these
degeneracies. We find that narrow-band photometry and spectroscopy yield
similar trends in the physical properties derived, the former being
considerably more precise. Using a galaxy sample from the SDSS, we compare more
realistically the results obtained from high-resolution and narrow-band SEDs
(synthesized from the same SDSS spectra) following the same spectral fitting
procedures. We use results from the literature as a benchmark to our
spectroscopic estimates and show that the prior PDFs, commonly adopted in
parametric methods, may introduce biases not accounted for in a Bayesian
framework. We conclude that narrow-band photometry yields the same trend in the
age-metallicity relation in the literature, provided it is affected by the same
biases as spectroscopy; albeit the precision achieved with the latter is
generally twice as large as with the narrow-band, at SNR values typical of the
different kinds of data.Comment: 26 pages, 15 figures. Accepted for publication in MNRA
Irregular sloshing cold fronts in the nearby merging groups NGC 7618 and UGC 12491: evidence for Kelvin-Helmholtz instabilities
We present results from two \sim30 ks Chandra observations of the hot
atmospheres of the merging galaxy groups centered around NGC 7618 and UGC
12491. Our images show the presence of arc-like sloshing cold fronts wrapped
around each group center and \sim100 kpc long spiral tails in both groups. Most
interestingly, the cold fronts are highly distorted in both groups, exhibiting
'wings' along the fronts. These features resemble the structures predicted from
non-viscous hydrodynamic simulations of gas sloshing, where Kelvin-Helmholtz
instabilities (KHIs) distort the cold fronts. This is in contrast to the
structure seen in many other sloshing and merger cold fronts, which are smooth
and featureless at the current observational resolution. Both magnetic fields
and viscosity have been invoked to explain the absence of KHIs in these smooth
cold fronts, but the NGC 7618/UGC 12491 pair are two in a growing number of
both sloshing and merger cold fronts that appear distorted. Magnetic fields
and/or viscosity may be able to suppress the growth of KHIs at the cold fronts
in some clusters and groups, but clearly not in all. We propose that the
presence or absence of KHI-distortions in cold fronts can be used as a measure
of the effective viscosity and/or magnetic field strengths in the ICM.Comment: ApJ, accepted. Uses emulateapj styl
AGN feedback and iron enrichment in the powerful radio galaxy, 4C+55.16
We present a detailed X-ray analysis of 4C+55.16, an unusual and interesting
radio galaxy, located at the centre of a cool core cluster of galaxies.
4C+55.16 is X-ray bright (L(cluster)~10^45 erg/s), radio powerful, and shows
clear signs of interaction with the surrounding intracluster medium. By
combining deep Chandra (100 ks) with 1.4 GHz VLA observations, we find evidence
of multiple outbursts from the central AGN, providing enough energy to offset
cooling of the ICM (P_bubbles=6.7x10^44 erg/s). Furthermore, 4C+55.16 has an
unusual intracluster iron distribution showing a plume-like feature rich in Fe
L emission that runs along one of the X-ray cavities. The excess of iron
associated with the plume is around 10^7M_sol. The metal abundances are
consistent with being Solar-like, indicating that both SNIa and SNII contribute
to the enrichment. The plume and southern cavity form a region of cool
metal-rich gas, and at the edge of this region, there is a clear discontinuity
in temperature (from kT~2.5 keV to kT~5.0 keV), metallicity (from ~0.4 solar to
0.8 solar), and surface brightness distribution, consistent with it being
caused by a cold front. However, we also suggest that this discontinuity could
be caused by cool metal-rich gas being uplifted from the central AGN along one
of its X-ray cavities.Comment: 12 pages, 11 figures, 1 table, Accepted to MNRAS (minor revision
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