arXiv subjects

Sebastian Heinz

Publications and source records attributed to Sebastian Heinz.

52 records · Page 3Linked to original sources

arXiv2009

Evolution of X-ray Cavities in Galaxy Clusters

The physics of X-ray cavities in galaxy clusters is constrained by their observed morphological evolution, which depends on such poorly-understood properties as the turbulent density field and magnetic fields. Here we combine numerical simulations that include subgrid turbulence and software that produces synthetic X-ray observations to examine the evolution of X-ray cavities in the the absence of magnetic fields. Our results reveal an anisotropic size evolution that is very different from simplified, analytical predictions. These differences highlight some of the key issues that must be accurately quantified when studying AGN-driven cavities, and help to explain why the inferred pV energy in these regions appears to be correlated with their distance from the cluster center. Interpreting X-ray observations will require detailed modeling of effects including mass-entrainment, distortion by drag forces, and projection. Current limitations do not allow a discrimination between purely hydrodynamic and magnetically-dominated models for X-ray cavities.

astro-ph.CO↗

arXiv2009

Evolution of X-ray cavities

A wide range of recent observations have shown that AGN-driven cavities may provide the energy source that balances the cooling observed in the centres of cool-core galaxy clusters. One tool for better understanding the physics of these cavities is their observed morphological evolution, which is dependent on such poorly-understood properties as the turbulent density field and the impact of magnetic fields. Here we combine numerical simulations that include subgrid turbulence and software that produces synthetic X-ray observations to examine the evolution of X-ray cavities in the absence of magnetic fields. Our results reveal an anisotropic size evolution of that is dramatically different from simplified, analytical predictions. These differences highlight some of the key issues that must be accurately quantified when studying AGN-driven cavities, and help to explain why the inferred pV energy in these regions appears to be correlated with their distance from the cluster center. Interpreting X- ray observations will require detailed modeling of effects including mass-entrainment, distortion by drag forces, and pro jection. Current limitations do not allow a discrimination between purely hydrodynamic and magnetically-dominated models for X-ray cavities.

astro-ph.GA↗

arXiv2008

A synthesis model for AGN evolution: supermassive black holes growth and feedback modes

We present a comprehensive synthesis model for the AGN evolution and the growth of supermassive black holes in the Universe. We solve the continuity equation for SMBH mass function using the locally determined one as a boundary condition, and the hard X-ray luminosity function as tracer of the AGN growth rate distribution, supplemented with a luminosity-dependent bolometric correction and an absorbing column distribution. Differently from most previous semi-analytic and numerical models, we do not assume any specific distribution of Eddington ratios, rather we determine it empirically by coupling the mass and luminosity functions. SMBH show a very broad accretion rate distribution, and we discuss the consequences of this fact for our understanding of observed AGN fractions in galaxies. We confirm previous results and demonstrate that, at least for z<1.5, SMBH mass function evolves anti-hierarchically, i.e. the most massive holes grew earlier and faster than less massive ones. For the first time, we find hints of a reversal of such a downsizing behaviour at redshifts above the peak of the black hole accretion rate density (z~2). We also derive tight constraints on the (mass weighted) average radiative efficiency of AGN: we find that 0.065<ξ_0 ε_{rad}< 0.07$, where ξ_0 is the local SMBH mass density in units of 4.3x10^5 M_sun Mpc^{-3}. We trace the cosmological evolution of the kinetic luminosity function of AGN, and find that the overall efficiency of SMBH in converting accreted rest mass energy into kinetic power, ranges between 3 and 5 \times 10^{-3}. Such a ``kinetic efficiency'' varies however strongly with SMBH mass and redshift, being maximal for very massive holes at late times, as required for the AGN feedback by many galaxy formation models in Cosmological contexts. (Abriged)

astro-ph↗

arXiv2008

Modeling the SS 433 Jet Bends

We fit Chandra HETGS data obtained for the unusual X-ray binary SS 433. While line strengths and continuum levels hardly change, the jet Doppler shifts show aperiodic variations that probably result from shocks in interactions with the local environment. The X-ray and optical emission line regions are found to be related but not coincident as the optical line emission persists for days while the X-ray emission lines fade in less than 5000 s. The X-ray spectrum of the blue-shifted jet shows over two dozen emission lines from plasma at a variety of temperatures. The emission measure distribution derived from the spectrum can be used to test jet cooling models.

astro-ph↗

arXiv2008

A deep Chandra observation of Abell 4059: a new face to radio-mode AGN feedback?

A deep Chandra observation of the cooling core cluster Abell 4059 (A4059) is presented. Previous studies have found two X-ray cavities in the central regions of A4059 together with a ridge of X-ray emission 20kpc south-west of the cluster center. These features are clearly related to the radio galaxy PKS2354-35 which resides in the cD galaxy. Our new data confirm these previous findings and strengthen previous suggestions that the south-western ridge is colder and denser than, but in approximate pressure equilibrium with, the surrounding ICM atmosphere. In addition, we find evidence for a weak shock that wraps around the north and east sides of the cavity structure. Our data allow us to map the 2-dimensional distribution of metals in the ICM of A4059 for the first time. We find that the SW ridge possesses an anomalously high (super-solar) metalicity. The unusual morphology, temperature structure and metal distribution all point to significant asymmetry in the ICM atmosphere prior to the onset of radio-galaxy activity. Motivated by the very high metalicity of the SW ridge, we hypothesize that the ICM asymmetry was caused by the extremely rapid stripping of metal enriched gas from a starburst galaxy that plunged through the core of A4059. Furthermore, we suggest that the onset of powerful radio-galaxy activity in the cD galaxy may have been initiated by this starburst/stripping event, either via the tidal-shocking of cold gas native to the cD galaxy, or the accretion of cold gas that had been stripped from the starburst galaxy.

astro-ph↗

arXiv2007

Measuring the kinetic power of AGN in the radio mode

(Abridged) We have studied the relationship among nuclear radio and X-ray power, Bondi rate and the kinetic luminosity of sub-Eddington active galactic nuclear (AGN) jets. Besides the recently discovered correlation between jet kinetic and Bondi power, we show that a clear correlation exists also between Eddington-scaled kinetic power and bolometric luminosity, given by: Log(L_kin/L_Edd)=0.49*Log(L_bol/L_Edd)-0.78. The measured slope suggests that these objects are in a radiatively inefficient accretion mode, and has been used to put stringent constraints on the properties of the accretion flow. We found no statistically significant correlations between Bondi power and bolometric AGN luminosity, apart from that induced by their common dependence on L_kin. Analyzing the relation between kinetic power and radio core luminosity, we are then able to determine, statistically, both the probability distribution of the mean jets Lorentz factor, peaking at Γ~7, and the intrinsic relation between kinetic and radio core luminosity, that we estimate as: Log(L_kin)=0.81*Log(L_R)+11.9, in good agreement with theoretical predictions of synchrotron jet models. With the aid of these findings, quantitative assessments of kinetic feedback from supermassive black holes in the radio mode will be possible based on accurate determinations of the central engine properties alone. As an example, Sgr A* may follow the correlations of radio mode AGN, based on its observed radiative output and on estimates of the accretion rate both at the Bondi radius and in the inner flow. If this is the case, the SMBH in the Galactic center is the source of ~ 5 times 10^38 ergs/s of mechanical power, equivalent to about 1.5 supernovae every 10^5 years.

astro-ph↗

arXiv2007

The kinetic luminosity function and the jet production efficiency of growing black holes

We derive the kinetic luminosity function for flat spectrum radio jets, using the empirical and theoretical scaling relation between jet power and radio core luminosity. The normalization for this relation is derived from a sample of flat spectrum cores in galaxy clusters with jet-driven X-ray cavities. The total integrated jet power at z=0 is W_{tot} ~ 3x10^40 ergs/s/Mpc^{3}. By integrating W_{tot} over red-shift, we determine the total energy density deposited by jets as e_{tot} ~ 2x10^{58} ergs/Mpc^{3}. Both W_{tot} and e_{tot} are dominated by low luminosity sources. Comparing e_{tot} to the local black hole mass density rho_{BH} gives an average jet production efficiency of epsilon_{jet} = e_{jet}/rho_{BH}c^2 ~ 3%. Since black hole mass is accreted mainly during high luminosity states, epsilon_{jet} is likely much higher during low luminosity states.

astro-ph↗

arXiv2005

Composition, collimation, contamination: the jet of Cygnus X-1

We model the observed size and brightness of the VLBA radio core of the jet in Cygnus X-1 to derive an expression for the jet power as a function of basic jet parameters. We apply this expression to recent constraints on the jet power from observations of a large scale shocked shell around the source by Gallo et al. 2005, which leads us to a set of alternative conclusions: either (a) the jet contains large amounts of protons: more than 2000 protons per radio emitting electron, (b) it has a very low radio volume filling factor of f < 3x10^(-5), (c) the steady, radio emitting VLBA jet is not the source of the kinetic energy powering the ISM shell, or (d) its asymptotic behavior differs fundamentally from a broad set of plausible analytic jet models.

astro-ph↗

arXiv2005

Is the `IR Coincidence' Just That?

(Abridged) Motch (1985) suggested that in the hard state of GX 339-4 the soft X-ray power-law extrapolated backward in energy agrees with the IR flux. Corbel & Fender (2002) showed that the hard state radio power-law extrapolated forward in energy meets the extrapolated X-ray power-law at an IR break, which was explicitly observed twice in GX 339-4. This `IR coincidence' has been cited as further evidence that a jet might make a significant contribution to the X-rays in hard state systems. We explore this hypothesis with a series of simultaneous radio/X-ray observations of GX 339-4, taken during its 1997, 1999, and 2002 hard states. We fit these spectra, in detector space, with a simple, but remarkably successful, doubly broken power-law that requires an IR spectral break. For these observations, the break position and the integrated radio/IR flux have stronger dependences upon the X-rays than the simplest jet predictions. If one allows for a softening of the X-ray power law with increasing flux, then the jet model agrees with the correlation. We also find evidence that the radio/X-ray fcorrelation previously observed in GX 339-4 shows a `parallel track' for the 2002 hard state. The slope of the 2002 correlation is consistent with prior observations; however, the radio amplitude is reduced. We then examine the correlation in Cyg X-1 through the use of radio data, obtained with the Ryle radio telescope, and RXTE data, from the ASM and pointed observations. We again find evidence of `parallel tracks', and here they are associated with `failed transitions' to the soft state. We also find that for Cyg X-1 the radio flux is more fundamentally correlated with the hard X-ray flux.

astro-ph↗

arXiv2004

A fundamental plane of black hole activity: pushing forward the unification scheme

We examine the disc--jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the hard X-ray and radio bands. We compile a sample of ~100 active galactic nuclei with measured mass, 5 GHz core emission, and 2-10 keV luminosity, together with 8 galactic black holes with a total of about 50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_R) and the X-ray (L_X) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with both M and L_X, at a highly significant level. We show how this result can be used to extend the standard unification by orientation scheme to encompass unification by mass and accretion rate.

astro-ph↗

arXiv2004

Observations of Abell 4059 with Chandra, HST and VLA: unraveling a complex cluster/radio-galaxy interaction

(abridged) We present a detailed reanalysis of the Chandra data for the galaxy cluster Abell 4059 and its central radio galaxy, PKS2354-35. We also present new 1.4GHz and 4.7GHz CnB-array radio data from the Very Large Array (VLA), as well as a short archival WFPC2 image from the Hubble Space Telescope. The presence of a strong interaction between this radio galaxy and the intracluster medium (ICM) was suggested by Huang & Sarazin (1998) on the basis of a short observation by the High Resolution Imager on ROSAT, and confirmed in our preliminary analysis of the Chandra/ACIS-S data. In particular, X-ray imaging clearly shows two cavities within the ICM that are approximately aligned with the radio-galaxy axis. However, using our new radio maps we fail to find a detailed correspondence between the 1 arcmin scale radio-lobes and the ICM cavities. This suggests that the cavities are ``ghosts'' of a previous burst of powerful activity by PKS 2354-35. We also examine the nature of the central asymmetric ridge (or bar) of X-ray emission extending for 30kpc south-west of the cluster center that has been noted in these previous analyzes. We find the ridge to be denser and cooler than, but probably in pressure balance with, its surroundings. The thermal evolution of this structure seems to be dominated by radiative cooling, possibly enhanced by the radio-galaxy ICM interaction. We discuss several possible models for the formation of this SW ridge and find none of them to be entirely satisfactory.

astro-ph↗

arXiv2003

A fundamental plane of black hole activity

We examine the disc--jet connection in stellar mass and supermassive black holes by investigating the properties of their compact emission in the X-ray and radio bands. We compile a sample of ~100 active galactic nuclei with measured mass, 5 GHz core emission, and 2-10 keV luminosity, together with 8 galactic black holes with a total of ~50 simultaneous observations in the radio and X-ray bands. Using this sample, we study the correlations between the radio (L_{R}) and the X-ray (L_{X}) luminosity and the black hole mass (M). We find that the radio luminosity is correlated with {\em both} M and L_{X}, at a highly significant level. In particular, we show that the sources define a ``fundamental plane'' in the three-dimensional (log L_{R},log L_{X},log M) space, given by log L_{R}=(0.60^{+0.11}_{-0.11}) log L_{X} +(0.78^{+0.11}_{-0.09}) log M + 7.33^{+4.05}_{-4.07}, with a substantial scatter of σ_{R}=0.88. We compare our results to the theoretical relations between radio flux, black hole mass, and accretion rate derived by Heinz and Sunyaev (2003). Such relations depend only on the assumed accretion model and on the observed radio spectral index. Therefore, we are able to show that the X-ray emission from black holes accreting at less than a few per cent of the Eddington rate is unlikely to be produced by radiatively efficient accretion, and is marginally consistent with optically thin synchrotron emission from the jet. On the other hand, models for radiatively inefficient accretion flows seem to agree well with the data.

astro-ph↗

arXiv2002

Hiding in Plain Sight: Chandra Observations of the Quiescent Neutron Star 4U 2129+47 in Eclipse

During a previous outburst phase, the neutron star 4U 2129+47 exhibited evidence for a spatially extended corona via broad, partial X-ray eclipses occurring periodically on the 5.24 hr orbit. Since 1983, however, 4U 2129+47 has entered a quiescent state several orders of magnitude fainter. We have performed a 37 ksec Chandra observation of 4U 2129+47 to determine whether an extended coronal structure also exists in quiescence. Total eclipses are found, and the rapidity of the eclipse ingress and egress are used to place upper limits on the size of the X-ray source. The spectrum is comprised of a soft component plus a fairly hard power law tail. The former is seen to be sinusoidally modulated over the orbital period in a manner consistent with neutral column variations, possibly due to the interaction of an accretion stream with a (small) disk about the neutron star. We fit realistic atmosphere models to the soft spectra, and comment on the consistency of the spectra with cooling neutron star models. It has been suggested that the 4U 2129+47 system is a hierarchical triple, with the outer body being an F star. We use differential astrometry to show that the X-ray point source and F star are spatially coincident to within 0.1". We further compare newly determined upper limits for the extrinsic neutral column to the reddening of the F star. Finally, we discuss how future X-ray observations can further constrain models of quiescent neutron star emission, as well as directly verify the triple hypothesis.

astro-ph↗

arXiv2002

Radio and X-Ray Detectability of Buoyant Radio Plasma Bubbles in Clusters of Galaxies

The Chandra X-ray Observatory is finding a surprisingly large number of cavities in the X-ray emitting intracluster medium, produced by the release of radio plasma from active galactic nuclei. In this Letter, we present simple analytic formulae for the evolution of the X-ray deficit and for the radio spectrum of a buoyantly rising bubble. The aim of this work is to provide a theoretical framework for the planning and the analysis of X-ray and radio observations of galaxy clusters. We show that the cluster volume tested for the presence of cavities by X-ray observations is a strongly rising function of the sensitivity.

astro-ph↗

arXiv2002

Chandra ACIS-S Observations of Abell 4059: Signs of Dramatic Interaction Between a Radio Galaxy and a Galaxy Cluster

We present Chandra observations of the galaxy cluster A4059. We find strong evidence that the FR-I radio galaxy PKS 2354-35 at the center of A4059 is inflating cavities with radii ~20 kpc in the intracluster medium, similar to the situation seen in Perseus A and Hydra A. We also find evidence for interaction between the intracluster medium and PKS 2354-35 on small scales in the very center of the cluster. Arguments are presented suggesting that this radio galaxy has faded significantly in radio power (possibly from an FR-II state) over the past 10^8 yrs.

astro-ph↗

arXiv1998

X-ray Signatures of Evolving Radio Galaxies

We present a simple model for an evolving radio galaxy, as it expands into the hot, X-ray emitting interstellar medium (ISM) of its host galaxy or similarly into the hot intracluster medium (ICM) of its host cluster. We solve the governing equations numerically on a grid of model parameters in order to present simple analytical tools for X-ray observations of the shocked shell that is pushed out by the cocoon and the associated cavity in the cluster emission. We apply these tools to the well known example of Perseus A to show that its time-averaged kinetic luminosity probably exceeds 10^46 ergs/sec, much larger than the estimated current power. We show how future observations can be used to extract useful source parameters such as the average kinetic power and the source age, and discuss detectability of sources at various stages of their lives.

astro-ph↗