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Register a new userMeasuring bulk flows of the intracluster medium in the Perseus and Coma galaxy clusters using XMM-Newton
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We demonstrate a novel technique for calibrating the energy scale of the XMM EPIC-pn detector, which allows us to measure bulk flows in the intracluster medium (ICM) of the Perseus and Coma clusters. The procedure uses the instrumental lines present in all observations, in particular, Cu-Ka. By studying their spatial and temporal variations, in addition to incorporating calibration observations, we refined the absolute energy scale to better than 150 km/s at the Fe-K line, a large improvement over the nominal accuracy of 550 km/s. We then mapped the bulk motions over much of the central 1200 and 800 kpc of Perseus and Coma, respectively, in spatial regions down to 65 and 140 kpc size. We cross-checked our procedure by comparing our measurements with those found in Perseus by Hitomi for an overlapping region, finding consistent results. For Perseus, there is a LoS velocity increase of 480+-210 km/s (1sigma) 250 kpc east of the nucleus. This region is associated with a cold front, providing direct evidence of the ICM sloshing in the potential well. Assuming the intrinsic distribution of bulk motions is Gaussian, its width is 214+-85 km/s, excluding systematics. Removing the sloshing region, this is reduced to 20-150 km/s, which is similar in magnitude to the Hitomi line width measurements in undisturbed regions. In Coma, the line-of-sight velocity of the ICM varies between the velocities of the two central galaxies. Maps of the gas velocity and metallicity provide clues about the merger history of the Coma, with material to the north and east of the cluster core having a velocity similar to NGC 4874, while that to the south and west has velocities close to NGC 4889. Our results highlight the difference between a merging system, such as Coma, where we observe a ~1000 km/s range in velocity, and a relatively relaxed system, such as Perseus, with much weaker bulk motions. [abridged]
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Based on XMM-Newton observations of a sample of galaxy clusters, we have measured the elemental abundances (mainly O, Si, S, and Fe) and their spatial distributions in the intracluster medium (ICM). In the outer region of the ICM, observations of the O:Si:S:Fe ratio are consistent with the solar value, suggesting that the metals in the ICM were produced by a mix of supernovae (SNe) Ia and II. On the other hand, around the cD galaxy, the O/Fe ratios are about half of the solar value because of a central excess of the Fe abundance. An increase of the relative contribution from SNe Ia in the cD galaxy to the metal production towards the center is the most likely explanation.
Clusters of galaxies are the most massive gravitationally-bound objects in the Universe and are still forming. They are thus important probes of cosmological parameters and a host of astrophysical processes. Knowledge of the dynamics of the pervasive hot gas, which dominates in mass over stars in a cluster, is a crucial missing ingredient. It can enable new insights into mechanical energy injection by the central supermassive black hole and the use of hydrostatic equilibrium for the determination of cluster masses. X-rays from the core of the Perseus cluster are emitted by the 50 million K diffuse hot plasma filling its gravitational potential well. The Active Galactic Nucleus of the central galaxy NGC1275 is pumping jetted energy into the surrounding intracluster medium, creating buoyant bubbles filled with relativistic plasma. These likely induce motions in the intracluster medium and heat the inner gas preventing runaway radiative cooling; a process known as Active Galactic Nucleus Feedback. Here we report on Hitomi X-ray observations of the Perseus cluster core, which reveal a remarkably quiescent atmosphere where the gas has a line-of-sight velocity dispersion of 164+/-10 km/s in a region 30-60 kpc from the central nucleus. A gradient in the line-of-sight velocity of 150+/-70 km/s is found across the 60 kpc image of the cluster core. Turbulent pressure support in the gas is 4% or less of the thermodynamic pressure, with large scale shear at most doubling that estimate. We infer that total cluster masses determined from hydrostatic equilibrium in the central regions need little correction for turbulent pressure.
The XMM-Newton Distant Cluster Project (XDCP) aims at the identification of a well defined sample of X-ray selected clusters of galaxies at redshifts z>0.8. We present a catalogue of the extended sources in one the deepest ~250 ksec XMM-Newton fields targeting LBQS 2215-175 covering the CFHTLS deep field four. The cluster identification is based, among others, on deep imaging with the ESO VLT and from the CFHT legacy survey. The confirmation of cluster candidates is done by VLT/FORS2 multi-object spectroscopy. Photometric redshifts from the CFHTLS D4 are utilized to confirm the effectiveness of the X-ray cluster selection method. The survey sensitivity is computed with extensive simulations. At a flux limit of S(0.5-2.0 keV) ~ 2.5e-15 erg/s we achieve a completeness level higher than 50% in an area of ~0.13 square degrees. We detect six galaxy clusters above this limit with optical counterparts, of which 5 are new spectroscopic discoveries. Two newly discovered X-ray luminous galaxy clusters are at z>1.0, another two at z=0.41 and one at z=0.34. For the most distant X-ray selected cluster in this field at z=1.45 we find additional (active) member galaxies from both X-ray and spectroscopic data. Additionally, we find evidence of large scale structures at moderate redshifts of z=0.41 and z=0.34. The quest for distant clusters in archival XMM-Newton data has led to the detection of six clusters in a single field, making XMM-Newton an outstanding tool for cluster surveys. Three of these clusters are at z>1, which emphasises the valuable contribution of small, yet deep surveys to cosmology. Beta-models are appropriate descriptions for the cluster surface brightness to perform cluster detection simulations in order to compute the X-ray selection function. The constructed logN-logS tends to favour a scenario where no evolution in the cluster X-ray luminosity function (XLF) takes place.
The extreme environment provided by the Cartwheel ring is analyzed to study its X-ray and optical-UV properties. We compare the Cartwheel with the other members of its group and study the system as a whole in the X-ray band. We analyze the data of the Cartwheel galaxy obtained with XMM-Newton in two different periods (December 2004 and May 2005). We focus on the X-ray properties of the system and use the OM data to obtain additional information in the optical and UV bands. We detect a total of 8 sources associated with the Cartwheel galaxy and three in its vicinity, including G1 and G2, all at L >= 10^39 erg/s, that is the Ultra Luminous X-ray (ULX) source range. The brightest ULX source has been already discussed elsewhere. The spectra of the next three brightest ULX are well fitted by a power-law model with a mean photon index of ~2. We compare the XMM-Newton and Chandra datasets to study the long-term variability of the sources. At least three sources vary in the 5 months between the two XMM-Newton observations and at least four in the 4-year timeframe between Chandra and XMM-Newton observations. One Chandra source disappears and a new one is detected by XMM-Newton in the ring. Optical-UV colors of the Cartwheel ring are consistent with a burst of star formation that is close to reaching its maximum, yielding a mean stellar age of about 40 Myr. The inferred variability and age suggest that high mass X-ray binaries are the counterparts to the ULX sources. The 3 companion galaxies have luminosities in the range 10^39-40 erg/s consistent with expectations. The hot gas of the Cartwheel galaxy is luminous and abundant (a few 10^8 Msol) and is found both in the outer ring, and in the inner part of the galaxy, behind the shock wave front. We also detect gas in the group with L_X ~10^40 erg/s.
Buoyant bubbles of relativistic plasma in cluster cores plausibly play a key role in conveying the energy from a supermassive black hole to the intracluster medium (ICM) - the process known as radio-mode AGN feedback. Energy conservation guarantees that a bubble loses most of its energy to the ICM after crossing several pressure scale heights. However, actual processes responsible for transferring the energy to the ICM are still being debated. One attractive possibility is the excitation of internal waves, which are trapped in the clusters core and eventually dissipate. Here we show that a sufficient condition for efficient excitation of these waves in stratified cluster atmospheres is flattening of the bubbles in the radial direction. In our numerical simulations, we model the bubbles phenomenologically as rigid bodies buoyantly rising in the stratified cluster atmosphere. We find that the terminal velocities of the flattened bubbles are small enough so that the Froude number ${rm Fr}lesssim 1$. The effects of stratification make the dominant contribution to the total drag force balancing the buoyancy force. In particular, clear signs of internal waves are seen in the simulations. These waves propagate horizontally and downwards from the rising bubble, spreading their energy over large volumes of the ICM. If our findings are scaled to the conditions of the Perseus cluster, the expected terminal velocity is $sim100-200{,rm km,s^{-1}}$ near the cluster cores, which is in broad agreement with direct measurements by the Hitomi satellite.
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