3 research outputs found
Metal transport by gas sloshing in M87
We present the results of an XMM-Newton mosaic covering the central ~200 kpc
of the nearby Virgo cluster. We focus on a strong surface brightness
discontinuity in the outskirts of the brightest cluster galaxy, M87. Using both
XMM-Newton and Suzaku, we derive accurate temperature and metallicity profiles
across this feature and show that it is a cold front probably due to sloshing
of the Virgo ICM. It is also associated with a discontinuity in the chemical
composition. The gas in the inner, bright region of the front is ~40% more
abundant in Fe than the gas outside the front, suggesting the important role of
sloshing in transporting metals through the ICM. For the first time, we provide
a quantitative estimate of the mass of Fe transported by a cold front. This
amounts to ~6% of the total Fe mass within the radial range affected by
sloshing, significantly more than the amount of metals transported by the AGN
in the same cluster core. The very low Fe abundance of only ~0.2 solar
immediately outside the cold front at a radius of 90 kpc suggests we are
witnessing first-hand the transport of higher metallicity gas into a pristine
region, whose abundance is typical of the cluster outskirts. The Mg/Fe and O/Fe
abundance ratios remain approximately constant over the entire radial range
between the centre of M87 and the faint side of the cold front, which requires
the presence of a centrally peaked distribution not only for Fe but also for
core-collapse type supernova products. This peak may stem from the star
formation triggered as the BCG assembled during the protocluster phase.Comment: accepted for publication in MNRA
The Interaction of 3C401 with the Surrounding Intracluster Medium
We present an observation of the radio-galaxy 3C401 and the surrounding
intracluster medium (ICM) of its host galaxy cluster by the Chandra X-ray
Observatory. This luminous radio-galaxy is notable in that it has
characteristics intermediate between the FRI and FRII morphologies. We clearly
detect point-like emission coincident with the radio-core of 3C401, although
the spatial resolution of even Chandra is only 2kpc at the distance of 3C401
(z=0.201) and so the possibility remains that this is a dense (and rapidly
cooling) thermal gaseous core in the center of the ICM atmosphere. Strong
departures from spherical symmetry in the central 10-20kpc of the ICM clearly
suggest interaction between the ICM and the radio-lobes of 3C401. A central
X-ray bar probably results from the evacuation of two ICM cavities by the
expanding radio lobes. Beyond these central regions, the cluster possesses a
flatter profile than many clusters of comparable mass suggesting the importance
of ICM heating and entropy injection by 3C401. We detect an interesting
cross-like structure in the ICM on 100kpc scales. We speculate that this could
be a radio-galaxy induced disturbance corresponding to a time when 3C401 was
substantially more powerful. A particularly exciting possibility is that this
cross-like structure corresponds to a large scale global g-mode oscillation
excited by a past outburst of 3C401.Comment: 7 pages, 5 postscript figures. Accepted for publication in MNRA
Studying Galactic interstellar turbulence through fluctuations in synchrotron emission First LOFAR Galactic foreground detection
<p>Aims. The characteristic outer scale of turbulence (i. e. the scale at which the dominant source of turbulence injects energy to the interstellar medium) and the ratio of the random to ordered components of the magnetic field are key parameters to characterise magnetic turbulence in the interstellar gas, which affects the propagation of cosmic rays within the Galaxy. We provide new constraints to those two parameters.</p><p>Methods. We use the LOw Frequency ARray (LOFAR) to image the diffuse continuum emission in the Fan region at (l, b) (137.0., + 7.0.) at 80 '' x 70 '' resolution in the range [146, 174] MHz. We detect multi-scale fluctuations in the Galactic synchrotron emission and compute their power spectrum. Applying theoretical estimates and derivations from the literature for the first time, we derive the outer scale of turbulence and the ratio of random to ordered magnetic field from the characteristics of these fluctuations.</p><p>Results. We obtain the deepest image of the Fan region to date and find diffuse continuum emission within the primary beam. The power spectrum displays a power law behaviour for scales between 100 and 8 arcmin with a slope a = -1.84 +/- 0.19. We find an upper limit of 20 pc for the outer scale of the magnetic interstellar turbulence toward the Fan region, which is in agreement with previous estimates in literature. We also find a variation of the ratio of random to ordered field as a function of Galactic coordinates, supporting different turbulent regimes.</p><p>Conclusions. We present the first LOFAR detection and imaging of the Galactic diffuse synchrotron emission around 160 MHz from the highly polarized Fan region. The power spectrum of the foreground synchrotron fluctuations is approximately a power law with a slope a beta-1.84 up to angular multipoles of similar to 1300, corresponding to an angular scale of similar to 8 arcmin. We use power spectra fluctuations from LOFAR as well as earlier GMRT andWSRT observations to constrain the outer scale of turbulence (Lout) of the Galactic synchrotron foreground, finding a range of plausible values of 10-20 pc. Then, we use this information to deduce lower limits of the ratio of ordered to random magnetic field strength. These are found to be 0.3, 0.3, and 0.5 for the LOFAR, WSRT and GMRT fields considered respectively. Both these constraints are in agreement with previous estimates.</p>