Virial shocks in galactic haloes? (original) (raw)
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The heating of gas in a galaxy cluster by X - ray cavities and large - scale shock fronts
Nature, 2005
Most of the baryons in galaxy clusters reside between the galaxies in a hot, tenuous gas 1 . The densest gas in their centres should cool and accrete onto giant central galaxies at rates of 10-1,000 solar masses per year 1 . No viable repository for this gas, such as clouds or new stars, has been found 1 . New X-ray observations, however, have revealed far less cooling below X-ray temperatures than expected 2 , altering the previously accepted picture of cooling flows. As a result, most of the gas must be heated to and maintained at temperatures above ,2 keV (ref. 3). The most promising heating mechanism is powerful radio jets emanating from supermassive black holes in the central galaxies of clusters 4 . Here we report the discovery of giant cavities and shock fronts in a distant (z 5 0.22) cluster caused by an interaction between a radio source and the hot gas surrounding it. The energy involved is ,6 3 10 61 erg, the most powerful radio outburst known. This is enough energy to quench a cooling flow for several Gyr, and to provide ,1/3 keV per particle of heat to the surrounding cluster.
Radiative shocks: New results for laboratory astrophysics
Journal de Physique IV (Proceedings), 2006
In the framework of the Laboratory Astrophysics, we present new radiative shocks experiments performed using the LULI2000 facility. A strong shock is driven in a multi-layered solid target (CH-Ti-CH) which accelerates into a gas cell (∼ 60 km/s) filled with Xenon at low pressure (0.1 − 0.3 bar) and produces a radiative supercritical shock .
X-ray emission from haloes of simulated disc galaxies
Monthly Notices of the Royal Astronomical Society, 2002
Bolometric and 0.2-2 keV X-ray luminosities of the hot gas haloes of simulated disc galaxies have been calculated at redshift z=0. The TreeSPH simulations are fully cosmological and the sample of 44 disc galaxies span a range in characteristic circular speeds of V c = 130-325 km s −1 . The galaxies have been obtained in simulations with a considerable range of physical parameters, varying the baryonic fraction, the gas metallicity, the meta-galactic UV field, the cosmology, the dark matter type, and also the numerical resolution. The models are found to be in agreement with the (few) relevant X-ray observations available at present. The amount of hot gas in the haloes is also consistent with constraints from pulsar dispersion measures in the Milky Way.
2010
We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between l = 120 • and l = 240 •. These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a singletemperature plasma model. We find that the observed halo temperature is fairly constant across the sky (∼(1.8-2.4)×10 6 K), whereas the halo emission measure varies by an order of magnitude (∼0.0005-0.006 cm −6 pc). When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in isolated extraplanar supernova remnants-this model predicts emission an order of magnitude too faint. A model of a supernova-driven interstellar medium, including the flow of hot gas from the disk into the halo in a galactic fountain, gives good agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of ∼2, but there are a several possible explanations for this discrepancy. We therefore conclude that a major (possibly dominant) contributor to the halo X-ray emission observed with XMM-Newton is a fountain of hot gas driven into the halo by disk supernovae. However, we cannot rule out the possibility that the extended hot halo of accreted material predicted by disk galaxy formation models also contributes to the emission.
THE ORIGIN OF THE HOT GAS IN THE GALACTIC HALO: CONFRONTING MODELS WITH XMM-NEWTON OBSERVATIONS
The Astrophysical Journal, 2010
We compare the predictions of three physical models for the origin of the hot halo gas with the observed halo X-ray emission, derived from 26 high-latitude XMM-Newton observations of the soft X-ray background between l = 120 • and l = 240 • . These observations were chosen from a much larger set of observations as they are expected to be the least contaminated by solar wind charge exchange emission. We characterize the halo emission in the XMM-Newton band with a singletemperature plasma model. We find that the observed halo temperature is fairly constant across the sky (∼(1.8-2.4)×10 6 K), whereas the halo emission measure varies by an order of magnitude (∼0.0005-0.006 cm −6 pc). When we compare our observations with the model predictions, we find that most of the hot gas observed with XMM-Newton does not reside in isolated extraplanar supernova remnants -this model predicts emission an order of magnitude too faint. A model of a supernova-driven interstellar medium, including the flow of hot gas from the disk into the halo in a galactic fountain, gives good agreement with the observed 0.4-2.0 keV surface brightness. This model overpredicts the halo X-ray temperature by a factor of ∼2, but there are a several possible explanations for this discrepancy. We therefore conclude that a major (possibly dominant) contributor to the halo X-ray emission observed with XMM-Newton is a fountain of hot gas driven into the halo by disk supernovae. However, we cannot rule out the possibility that the extended hot halo of accreted material predicted by disk galaxy formation models also contributes to the emission.
Hard X-ray emission from accretion shocks around galaxy clusters
Journal of Cosmology and Astroparticle Physics, 2010
We show that the hard X-ray (HXR) emission observed from several galaxy clusters is consistent with a simple model, in which the nonthermal emission is produced by inverse Compton scattering of cosmic microwave background photons by electrons accelerated in cluster accretion shocks: The dependence of HXR surface brightness on cluster temperature is consistent with that predicted by the model, and the observed HXR luminosity is consistent with the fraction of shock thermal energy deposited in relativistic electrons being 0.1. Alternative models, where the HXR emission is predicted to be correlated with the cluster thermal emission, are disfavored by the data. The implications of our predictions to future HXR observations (e.g. by NuStar, Simbol-X) and to (space/ground based) γ-ray observations (e.g. by Fermi, HESS, MAGIC, VERITAS) are discussed.
The Astrophysical Journal, 2011
We present deep spectroscopic observations of the classical T Tauri stars DF Tau and V4046 Sgr in order to better characterize two important sources of far-ultraviolet continuum emission in protoplanetary disks. These new Hubble Space Telescope-Cosmic Origins Spectrograph observations reveal a combination of line and continuum emission from collisionally excited H 2 and emission from accretion shocks. H 2 is the dominant emission in the 1400 λ 1650Å band spectrum of V4046 Sgr, while an accretion continuum contributes strongly across the far-ultraviolet spectrum of DF Tau. We compare the spectrum of V4046 Sgr to models of electron-impact induced H 2 emission to constrain the physical properties of the emitting region, after making corrections for attenuation within the disk. We find reasonable agreement with the broad spectral characteristics of the H 2 model, implying N (H 2 ) ∼ 10 18 cm −2 , T (H 2 ) = 3000 +1000 −500 K, and a characteristic electron energy in the range of ∼ 50 -100 eV. We propose that self-absorption and hydrocarbons provide the dominant attenuation for H 2 line photons originating within the disk. For both DF Tau and V4046 Sgr, we find that a linear fit to the far-UV data can reproduce near-UV/optical accretion spectra. We discuss outstanding issues concerning how these processes operate in protostellar/protoplanetary disks, including the effective temperature and absolute strength of the radiation field in low-mass protoplanetary environments. We find that the 912 -2000Å continuum in low-mass systems has an effective temperature of ∼ 10 4 K with fluxes 10 5−7 times the interstellar level at 1 AU.
Radiative shocks: An opportunity to study laboratory astrophysics
Physics of Plasmas, 2006
In this paper, experimental results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Two sets of experiments have been performed at the Laser pour l'Utilisation des Lasers Intenses ͑LULI͒ laboratory. Several shock parameters were simultaneously measured: shock temperature and velocities, the precursor two-dimensional ͑2D͒ time evolution, its electron density, density gradient, and temperature. Data were obtained varying initial conditions for different laser intensities and gas pressures. Comparisons with 1D and 2D radiative hydrodynamic simulations are shown for all measured parameters ͑shock velocity, shape, radial expansion, and temperature as well as precursor velocity and electron density͒.
Testing for Shock-heated X-Ray Gas around Compact Steep Spectrum Radio Galaxies
The Astrophysical Journal, 2017
We present Chandra and XMM-Newton X-ray, Very Large Array (VLA) radio, and optical observations of three candidate compact steep spectrum (CSS) radio galaxies. CSS sources are of a galactic scale and are presumably driving a shock through the interstellar medium (ISM) of their host galaxy. B3 1445+410 is a low-excitation emission line CSS radio galaxy with possibly a hybrid Fanaroff-Riley FRI/II (or fat double) radio morphology. The Chandraobservations reveal a point-like source that is well fit with a power law consistent with the emission from a Doppler boosted core. 3C 268.3 is a CSS broad-line radio galaxy (BLRG) whose Chandra data are consistent spatially with a point source centered on the nucleus and spectrally with a double power-law model. PKS B1017-325 is a low-excitation emission line radio galaxy with a bent double radio morphology. While from our new spectroscopic redshift, PKS B1017−325 falls outside the formal definition of a CSS, the XMM-Newton observations are consistent with ISM emission with either a contribution from hot shocked gas or non-thermal jet emission. We compile selected radio and X-ray properties of the nine bona fide CSS radio galaxies with X-ray detections so far. We find that two out of the nine show X-ray spectroscopic evidence for hot shocked gas. We note that the counts in the sources are low and that the properties of the two sources with evidence for hot shocked gas are typical of the other CSS radio galaxies. We suggest that hot shocked gas may be typical of CSS radio galaxies due to their propagation through their host galaxies.
Shock heating in the group atmosphere of the radio galaxy B2 0838+32A
Monthly Notices of The Royal Astronomical Society, 2008
We present Chandra and radio observations, and analysis of Sloan Digital Sky Survey data, of the radio galaxy B2 0838+32A (4C 32.26) and its environment. The radio galaxy is at the centre of a nearby group that has often been identified with the cluster Abell 695, but we argue that the original Abell cluster is likely to be an unrelated and considerably more distant system. The radio source is a restarting radio galaxy and, using our Chandra data, we argue that the currently active lobes are expanding supersonically, driving a shock with Mach number 2.4 +1.0 −0.5 into the inter-stellar medium. This would be only the third strong shock round a young radio source to be discovered, after Centaurus A and NGC 3801. However, in contrast to both these systems, the host galaxy of B2 0838+32A shows no evidence for a recent merger, while the AGN spectrum shows no evidence for the dusty torus that would imply a large reservoir of cold gas close to the central black hole. On the contrary, the AGN spectrum is of a type that has been associated with the presence of a radiatively inefficient accretion flow that could be controlled by AGN heating and subsequent cooling of the hot, X-ray emitting gas. If correct, this means that B2 0838+32A is the first source in which we can directly see entropy-increasing processes (shocks) driven by accretion from the hot phase of the interstellar medium.