94 research outputs found
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
Stormy weather in 3C 196.1: nuclear outbursts and merger events shape the environment of the hybrid radio galaxy 3C 196.1
We present a multi-wavelength analysis based on archival radio, optical and
X-ray data of the complex radio source 3C 196.1, whose host is the brightest
cluster galaxy of a cluster. HST data show H+[N II] emission
aligned with the jet 8.4 GHz radio emission. An H+[N II] filament
coincides with the brightest X-ray emission, the northern hotspot. Analysis of
the X-ray and radio images reveals cavities located at galactic- and cluster-
scales. The galactic-scale cavity is almost devoid of 8.4 GHz radio emission
and the south-western H+[N II] emission is bounded (in projection) by
this cavity. The outer cavity is co-spatial with the peak of 147 MHz radio
emission, and hence we interpret this depression in X-ray surface brightness as
being caused by a buoyantly rising bubble originating from an AGN outburst
280 Myrs ago. A \textit{Chandra} snapshot observation allowed us to
constrain the physical parameters of the cluster, which has a cool core with a
low central temperature 2.8 keV, low central entropy index 13 keV
cm and a short cooling time of 500 Myr, which is of the age
of the Universe at this redshift. By fitting jumps in the X-ray density we
found Mach numbers between 1.4 and 1.6, consistent with a shock origin. We also
found compelling evidence of a past merger, indicated by a morphology
reminiscent of gas sloshing in the X-ray residual image. Finally, we computed
the pressures, enthalpies and jet powers associated with
the cavities: erg,
erg s for the inner cavity and erg,
erg s for the outer cavity.Comment: 14 pages, 4 figures, ApJ accepte
METALS IN THE ICM: WITNESSES OF CLUSTER FORMATION AND EVOLUTION
The baryonic composition of galaxy clusters and groups is dominated by a hot, X-ray emitting Intra-Cluster Medium (ICM). The mean metallicity of the ICM has been found to be roughly 0.3 ÷ 0.5 times the solar value, therefore a large fraction of this gas cannot be of purely primordial origin. Indeed, the distribution and amount of metals in the ICM is a direct consequence of the past history of star formation in the cluster galaxies and of the processes responsible for the injection of enriched material into the ICM. We here shortly summarize the current views on the chemical enrichment, focusing on the observational evidence in terms of metallicity measurements in clusters, spatial metallicity distribution and evolution, and expectations from future missions
The intracluster magnetic field in the double relic galaxy cluster Abell 2345
Magnetic fields are ubiquitous in galaxy clusters, yet their radial profile, power spectrum, and connection to host cluster
properties are poorly known. Merging galaxy clusters hosting diffuse polarized emission in the form of radio relics offer a
unique possibility to study the magnetic fields in these complex systems. In this paper, we investigate the intracluster magnetic
field in Abell 2345. This cluster hosts two radio relics that we detected in polarization with 1–2 GHz Jansky Very Large Array
observations. X-ray XMM–Newton images show a very disturbed morphology. We derived the rotation measure (RM) of five
polarized sources within ∼1 Mpc from the cluster centre applying the RM synthesis. Both, the average RM and the RM dispersion
radial profiles probe the presence of intracluster magnetic fields. Using the thermal electron density profile derived from X-ray
analysis and simulating a 3D magnetic field with fluctuations following a power spectrum derived from magneto-hydrodynamical
cosmological simulations, we build mock RM images of the cluster. We constrained the magnetic field profile in the eastern
radio relic sector by comparing simulated and observed RM images. We find that, within the framework of our model, the data
require a magnetic field scaling with thermal electron density as B(r) ∝ n e (r). The best model has a central magnetic field (within
a 200 kpc radius) of 2.8±0.1 μG. The average magnetic field at the position of the eastern relic is ∼ 0.3 μG, a factor 2.7 lower
than the equipartition estimate
The intracluster magnetic field in the double relic galaxy cluster Abell 2345
High Energy Astrophysic
A 600 kpc complex radio source at the center of Abell 3718 discovered by the EMU and POSSUM surveys
Multifrequency studies of galaxy clusters are crucial for inferring their
dynamical states and physics. Moreover, these studies allow us to investigate
cluster-embedded sources, whose evolution is affected by the physical and
dynamical condition of the cluster itself. So far, these kinds of studies have
been preferentially conducted on clusters visible from the northern hemisphere
due to the high-fidelity imaging capabilities of ground-based radio
interferometers located there. In this paper, we conducted a multifrequency
study of the poorly known galaxy cluster Abell 3718. We investigated the
unknown origin of an extended radio source with a length of 612 kpc at
943 MHz detected in images from the Evolutionary Map of the Universe (EMU) and
POlarisation Sky Survey of the Universe's Magnetism (POSSUM) surveys. We
analyzed optical and X-ray data to infer the dynamical state of the cluster
and, in particular, the merger activity. We conducted a radio spectral index
study from 943 MHz up to 9 GHz. We also evaluated the polarization properties
of the brightest cluster-embedded sources to understand if they are related to
the radio emission observed on larger scales. [Abstract truncated due to arxiv
limit! Please see the pdf version]Comment: 12 pages, 10 figures; accepted for publication by A&
Extended X-ray study of M49: The frontier of the Virgo cluster
The M49 group, residing outside the virial radius of the Virgo cluster, is falling onto the cluster from the south. We report results from deep XMM-Newton mosaic observations of M49. Its hot gas temperature is 0.8 keV at the group center and rises to 1.5 keV beyond the brightest group galaxy (BGG). The group gas extends to radii of ~300 kpc to the north and south. The observations reveal a cold front ~20 kpc north of the BGG center and an X-ray-bright stripped tail 70 kpc long and 10 kpc wide to the southwest of the BGG. We argue that the atmosphere of the infalling group was slowed by its encounter with the Virgo cluster gas, causing the BGG to move forward subsonically relative to the group gas. We measure declining temperature and metallicity gradients along the stripped tail. The tail gas can be traced back to the cooler and enriched gas uplifted from the BGG center by buoyant bubbles, implying that active galactic nucleus outbursts may have intensified the stripping process. We extrapolate to a virial radius of 740 kpc and derive a virial mass of 4.6 × 1013 M ⊙ for the M49 group. Its group atmosphere appears truncated and deficient when compared with isolated galaxy groups of similar temperatures. If M49 is on its first infall to Virgo, the infall region of a cluster could have profound impacts on galaxies and groups that are being accreted onto galaxy clusters. Alternatively, M49 may have already passed through Virgo once
RELICS: The Reionization Lensing Cluster Survey and the Brightest High-z Galaxies
Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here the z ~ 6-8 candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of ≈200 arcmin². These clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the Cluster Lensing And Supernova survey with Hubble (CLASH). We discover 257, 57, and eight candidate galaxies at z ~ 6, 7, and 8 respectively, (322 in total). The observed (lensed) magnitudes of the z ~ 6 candidates are as bright as AB mag ~23, making them among the brightest known at these redshifts, comparable with discoveries from much wider, blank-field surveys. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the James Webb Space Telescope
The cluster gas mass fraction as a cosmological probe: a revised study
(Abriged) We present the analysis of the baryonic content of 52 X-ray
luminous galaxy clusters observed with Chandra in the redshift range 0.3-1.273.
We use the deprojected X-ray surface brightness profiles and the measured
values of the gas temperature to recover the gas and total mass profiles. By
assuming that galaxy clusters are representative of the cosmic baryon budget,
the distribution of the cluster baryon fraction in the hottest (T> 4 keV)
systems as a function of redshift is used to constrain the cosmological
parameters. We discuss how our constraints are affected by several systematics,
namely the isothermality, the assumed baryon fraction in stars, the depletion
parameter and the sample selection. By using only the cluster baryon fraction
as a proxy for the cosmological parameters, we obtain that Omega is very well
constrained at the value of 0.35 with a relative statistical uncertainty of 11%
(1 sigma level; w=-1) and a further systematic error of about (-6,+7)%. On the
other hand, constraints on Lambda (without the prior of flat geometry) and w
(using the prior of flat geometry) are definitely weaker due to the presence of
larger statistical and systematic uncertainties (of the order of 40 per cent on
Lambda and larger than 50 per cent on w). If the WMAP 5-year best-fit results
are assumed to fix the cosmological parameters, we limit the contributions
expected from non-thermal pressure support and ICM clumpiness to be lower than
about 10 per cent, leaving also room to accommodate baryons not accounted for
either in the X-ray emitting plasma or in stars of the order of 18 per cent of
the total cluster baryon budget.Comment: A&A in press. Accepted on March 28, 2009. Revised to match version in
prin
Abell 1430: A merging cluster with exceptional diffuse radio emission
Diffuse radio emission has been found in many galaxy clusters, predominantly
in massive systems which are in the state of merging. The radio emission can
usually be classified as relic or halo emission, which are believed to be
related to merger shocks or volume-filling turbulence, respectively. Recent
observations have revealed radio bridges for some pairs of very closeby galaxy
clusters. The mechanisms that may allow to explain the high specific density of
relativistic electrons, necessary to explain the radio luminosity of these
bridge regions, are poorly explored. We analyse the galaxy cluster Abell 1430
with LoTSS data in detail and complement it with recent JVLA L-band
observations, XMM-Newton, Chandra, and SDSS data. Moreover, we compare our
results to clusters extracted from the "The Three Hundred Project" cosmological
simulation. We find that Abell 1430 consists of two components, namely A1430-A
and A1430-B. We speculate that the two components undergo an off-axis merger.
The more massive component shows diffuse radio emission which can be classified
as radio halo showing a low radio power given the mass of the cluster. Most
interestingly, there is extended diffuse radio emission, dubbed as the
`Pillow', which is apparently related to A1430-B and thus related to low
density intracluster or intergalactic medium. To date, a only few examples for
emission originating from such regions are known. These discoveries are crucial
to constrain possible acceleration mechanisms, which may allow to explain the
presence of relativistic electrons in these regions. Our results indicate a
spectral index of for
the Pillow. If future observations confirm a slope as flat as the central value
of -1.4 or even flatter, this would pose a severe challenge for the electron
acceleration scenarios.Comment: 14 pages, 12 figures, accepted for publication in A&
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