1,620 research outputs found
Detecting X-ray filaments in the low redshift Universe with XEUS and Constellation-X
We propose a possible way to detect baryons at low redshifts from the
analysis of X-ray absorption spectra of bright AGN pairs. A simple
semi-analytical model to simulate the spectra is presented. We model the
diffuse warm-hot intergalactic medium (WHIM) component, responsible for the
X-ray absorption, using inputs from high-resolution hydro-dynamical simulations
and analytical prescriptions. We show that the number of OVII absorbers per
unit redshift with column density larger than cm -
corresponding to an equivalent width of 1 km/s - which will be possibly
detectable by {\it XEUS}, is \magcir 30 per unit redshift. {\it
Constellation-X} will detect OVII absorptions per unit redshift with
an equivalent width of 10 km/s. Our results show that, in a CDM
Universe, the characteristic size of these absorbers at is
Mpc. The filamentary structure of WHIM can be probed by finding
coincident absorption lines in the spectra of background AGN pairs. We estimate
that at least 20 AGN pairs at separation \mincir 20 arcmin are needed to
detect this filamentary structure at a 3 level. Assuming observations
of distant sources using {\it XEUS} for exposure times of 500 ksec, we find
that the minimum source flux to probe the filamentary structure is erg cm s, in the 0.1-2.4 keV energy band. Thus,
most pairs of these extragalactic X-ray bright sources have already been
identified in the {\it ROSAT} All-Sky Survey. Re-observation of these objects
by future missions could be a powerful way to search for baryons in the low
redshift Universe.Comment: 18 pages, 10 Figures. Two figures added, Sections 2 and 3 expanded.
More optimistic results for Constellation-X. Accepted by MNRA
Weighing simulated galaxy clusters using lensing and X-ray
We aim at investigating potential biases in lensing and X-ray methods to
measure the cluster mass profiles. We do so by performing realistic simulations
of lensing and X-ray observations that are subsequently analyzed using
observational techniques. The resulting mass estimates are compared among them
and with the input models. Three clusters obtained from state-of-the-art
hydrodynamical simulations, each of which has been projected along three
independent lines-of-sight, are used for this analysis. We find that strong
lensing models can be trusted over a limited region around the cluster core.
Extrapolating the strong lensing mass models to outside the Einstein ring can
lead to significant biases in the mass estimates, if the BCG is not modeled
properly for example. Weak lensing mass measurements can be largely affected by
substructures, depending on the method implemented to convert the shear into a
mass estimate. Using non-parametric methods which combine weak and strong
lensing data, the projected masses within R200 can be constrained with a
precision of ~10%. De-projection of lensing masses increases the scatter around
the true masses by more than a factor of two due to cluster triaxiality. X-ray
mass measurements have much smaller scatter (about a factor of two smaller than
the lensing masses) but they are generally biased low by 5-20%. This bias is
ascribable to bulk motions in the gas of our simulated clusters. Using the
lensing and the X-ray masses as proxies for the true and the hydrostatic
equilibrium masses of the simulated clusters and averaging over the cluster
sample we are able to measure the lack of hydrostatic equilibrium in the
systems we have investigated.Comment: 27 pages, 21 figures, accepted for publication on A&A. Version with
full resolution images can be found at
http://pico.bo.astro.it/~massimo/Public/Papers/massComp.pd
A2163: Merger events in the hottest Abell galaxy cluster II. Subcluster accretion with galaxy-gas separation
Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster
medium (ICM) that exhibits extraordinary properties, including an exceptionally
high X-ray luminosity, average temperature, and a powerful and extended radio
halo. The irregular and complex morphology of its gas and galaxy structure
suggests that this cluster has recently undergone major merger events that
involve two or more cluster components. In this paper, we study the gas
structure and dynamics by means of spectral-imaging analysis of X-ray data
obtained from XMM-Newton and Chandra observations. From the evidence of a cold
front, we infer the westward motion of a cool core across the E-W elongated
atmosphere of the main cluster A2163-A. Located close to a galaxy over-density,
this gas 'bullet' appears to have been spatially separated from its galaxy (and
presumably dark matter component) as a result of high-velocity accretion.
From gas brightness and temperature profile analysis performed in two
opposite regions of the main cluster, we show that the ICM has been
adiabatically compressed behind the crossing 'bullet' possibly because of shock
heating, leading to a strong departure of the ICM from hydrostatic equilibrium
in this region. Assuming that the mass estimated from the Yx proxy best
indicates the overall mass of the system and that the western cluster sector is
in approximate hydrostatic equilibrium before subcluster accretion, we infer a
merger scenario between two subunits of mass ratio 1:4, leading to a present
total system mass of M500 . The exceptional
properties of A2163 present various similarities with those of 1E0657-56, the
so-called 'bullet-cluster'. These similarities are likely to be related to a
comparable merger scenario.Comment: A&A, in pres
1WGAJ1226.9+3332: a high redshift cluster discovered by Chandra
We report the detection of 1WGAJ1226.9+3332 as an arcminute scale extended
X-ray source with the Chandra X-ray Observatory. The Chandra observation and R
and K band imaging strongly support the identification of 1WGAJ1226.9+3332 as a
high redshift cluster of galaxies, most probably at z=0.85 +- 0.15, with an
inferred temperature kT =10 (+4;-3) keV and an unabsorbed luminosity (in a
r=120" aperture) of 1.3 (+0.16;-0.14) x 1e45 erg/s (0.5-10 keV). This
indication of redshift is also supported by the K and R band imaging, and is in
agreement with the spectroscopic redshift of 0.89 found by Ebeling et al.
(2001). The surface brightness profile is consistent with a beta-model with
beta=0.770 +- 0.025, rc=(18.1 +-0.9)" (corresponding to 101 +- 5 kpc at
z=0.89), and S(0)=1.02 +- 0.08 counts/arcsec**2. 1WGAJ1226.9+3332 was selected
as an extreme X-ray loud source with FX/FV>60; this selection method, thanks to
the large area sampled, seems to be a highly efficient method for finding
luminous high z clusters of galaxies.Comment: 5 pages, 5 figures, 1 table. Accepted for publication in ApJ main
journal. Uses emulateapj.st
Temperature and total mass profiles of the A3571 cluster of galaxies
We present BeppoSAX results of a spatially resolved spectral analysis of A3571, a relaxed nearby cluster of galaxies. In the central 2' (130/h_50 kpc) radius the metal abundance is 0.49 +- 0.08 solar and the absorption (1.13 +-0.28) x 10^21 atom/cm^2 whereas elsewhere within an 8'(520/h_50 kpc) radius the abundance is 0.32 \+- 0.05 solar and the absorption consistent with the galactic value of 4.4 x 10^20 atom/cm2. The significant central metal abundance enhancement is consistent with the supernova enrichment scenario. The excess absorption may be attributed to the cooling flow, whose mass flow rate is 80 +- 40 M_Sun/yr from our spectral fit. The BeppoSAX and ASCA radial temperature profiles agree over the entire overlapping radial range r < 25' = 1.6/h_50 Mpc. The combined BeppoSAX and ASCA temperature profile exhibits a constant value out to a radius of 10' (650/h_50 kpc) and a significant decrease (T propto r^-0.55, corresponding to gamma=1.28) at larger radii. These temperature data are used to derive the total mass profile. The best fit NFW dark matter density model results in a temperature profile that is not convectively stable, but the model is acceptable within the uncertainties of the data. The temperature profile is acceptably modeled with a ``core'' model for the dark matter density, consisting of a core radius with a constant slope at larger radii. With this model the total mass and formal 90% confidence errors within the virial radius r_178 (2.5/h_50 Mpc) are 9.1+3.6-1.5 x 10^14 h_50^-1 M_Sun, by a factor of 1.4 smaller than the isothermal value. The gas mass fraction increases with radius, reaching f_gas(r_178) = 0.26+0.05-0.10 x h_50^-3/2. Assuming that the measured gas mass fraction is the lower limit to the primordial baryonic fraction gives Omega_m < 0.4 at 90% confidence
Are we missing baryons in Galaxy Clusters?
The recent constraints on the cosmological parameters put from the
observations of the WMAP satellite limit the cosmic baryon fraction in a range
that is larger than, and marginally consistent with, what is measured in galaxy
clusters. This rises the question whether or not we are considering all the
ingredients of cluster baryonic budget. Making a careful weight of the baryons
in X-ray emitting plasma and stars in cluster galaxies, I conclude that the
cluster baryonic pie is made by 13 (with a 1 sigma range of 8-19) per cent of
stars, 70 (56-89) per cent of intracluster hot medium and 17 (0-33) per cent,
and a probability of 73 per cent to be larger than 0, of ``other'' baryons,
presumably in the form of warm (1e5-1e7 Kelvin) material.Comment: MNRAS in press. Replaced to match proof, correct an error in the
determination of the total mass and update reference
Small-scale flows in SUMER and TRACE high-cadence co-observations
We report on the physical properties of small-scale transient flows observed
simultaneously at high cadence with the SUMER spectrometer and the TRACE imager
in the plage area of an active region. Our major objective is to provide a
better understanding of the nature of transient phenomena in the solar
atmosphere by using high-cadence imager and spectrometer co-observations at
similar spatial and temporal resolution. A sequence of TRACE Fe IX/X 171 A and
high-resolution MDI images were analysed together with simultaneously obtained
SUMER observations in spectral lines covering a temperature range from 10 000 K
to 1 MK. We reveal the existence of numerous transient flows in small-scale
loops (up to 30 Mm) observed in the plage area of an active region. These flows
have temperatures from 10 000 K (the low temperature limit of our observations)
to 250 000 K. The coronal response of these features is uncertain due to a
blending of the observed coronal line Mg X 624.85 A. The duration of the events
ranges from 60 s to 19 min depending on the loop size. Some of the flows reach
supersonic velocities. The Doppler shifts often associated with explosive
events or bi-directional jets can actually be identified with flows (some of
them reaching supersonic velocities) in small-scale loops. Additionally, we
demonstrate how a line-of-sight effect can give misleading information on the
nature of the observed phenomena if only either an imager or a spectrometer is
used.Comment: 7 pages, 6 figures, accepted by A&
GIADA performance during Rosetta mission scientific operations at comet 67P
The Grain Impact Analyser and Dust Accumulator (GIADA) instrument onboard Rosetta studied the dust environment of comet 67P/ChuryumovâGerasimenko from 3.7 au inbound, through perihelion, to 3.8 au outbound, measuring the dust flow and the dynamic properties of individual particles. GIADA is composed of three subsystems: 1) Grain Detection System (GDS); 2) Impact Sensor (IS); and 3) Micro-Balances System (MBS). Monitoring the subsystemsâ performance during operations is an important element for the correct calibration of scientific measurements. In this paper, we analyse the GIADA inflight calibration data obtained by internal calibration devices for the three subsystems during the period from 1 August 2014 to 31 October 2015. The calibration data testify a nominal behaviour of the instrument during these fifteen months of mission; the only exception is a minor loss of sensitivity for one of the two GDS receivers, attributed to dust contamination
Chandra Observation of Abell 2142: Survival of Dense Subcluster Cores in a Merger
We use Chandra data to map the gas temperature in the central region of the
merging cluster A2142. The cluster is markedly nonisothermal; it appears that
the central cooling flow has been disturbed but not destroyed by a merger. The
X-ray image exhibits two sharp, bow-shaped, shock-like surface brightness edges
or gas density discontinuities. However, temperature and pressure profiles
across these edges indicate that these are not shock fronts. The pressure is
reasonably continuous across these edges, while the entropy jumps in the
opposite sense to that in a shock (i.e. the denser side of the edge has lower
temperature, and hence lower entropy). Most plausibly, these edges delineate
the dense subcluster cores that have survived a merger and ram pressure
stripping by the surrounding shock-heated gas.Comment: Latex, 9 pages, 5 figures (including color), uses emulateapj.sty.
Submitted to Ap
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