arXiv subjects

Fabrizio Brighenti

Publications and source records attributed to Fabrizio Brighenti.

At least 37 records · Page 2Linked to original sources

arXiv2021

The central FR0 in the sloshing cluster Abell 795: Indications of mechanical feedback from Chandra data

We present a detailed study of the galaxy cluster Abell 795 and of its central Fanaroff-Riley Type 0 (FR0) radio galaxy. From an archival Chandra observation, we found a dynamically disturbed environment with evidences for sloshing of the intracluster medium. We argue that the environment alone cannot explain the compactness of the radio galaxy, as similar conditions are also found around extended sources. We identified a pair of putative X-ray cavities in the proximity of the center: These could have been created in a past outburst of the FR0, and dragged away by the large-scale gas movement. The presence of X-ray cavities associated with a FR0 could open a new window on the study of jet power and feedback properties of this recently discovered class of compact radio galaxies.

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arXiv2021

A Chandra study of Abell 795 -- a sloshing cluster with a FR0 radio galaxy at its center

We present the first X-ray dedicated study of the galaxy cluster A795 and of the Fanaroff-Riley Type 0 hosted in its brightest cluster galaxy. Using an archival 30 ks \textit{Chandra} observation we study the dynamical state and cooling properties of the intracluster medium, and we investigate whether the growth of the radio galaxy is prevented by the surrounding environment. We discover that A795 is a weakly cool core cluster, with an observed mass deposition rate $\lessapprox 14\,$ M$_{\odot}$yr$^{-1}$ in the cooling region (central $\sim$66 kpc). In the inner $\sim$ 30 kpc we identify two putative X-ray cavities, and we unveil the presence of two prominent cold fronts at $\sim$60 kpc and $\sim$178 kpc from the center, located along a cold ICM spiral feature. The central galaxy, which is offset by 17.7 kpc from the X-ray peak, is surrounded by a multi-temperature gas with an average density of $n_{\text{e}} = 2.14 \times 10^{-2}$ cm$^{-3}$. We find extended radio emission at 74-227 MHz centered on the cluster, exceeding the expected flux from the radio galaxy extrapolated at low frequency. We propose that sloshing is responsible for the spiral morphology of the gas and the formation of the cold fronts, and that the environment alone cannot explain the compactness of the radio galaxy. We argue that the power of the two cavities and the sloshing kinetic energy can reduce and offset cooling. Considering the spectral and morphological properties of the extended radio emission, we classify it as a candidate radio mini-halo.

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arXiv2021

A first Chandra view of the cool core cluster A1668: offset cooling and AGN feedback cycle

We present a multi-wavelength analysis of the galaxy cluster A1668, performed by means of new EVLA and Chandra observations and archival H$α$ data. The radio images exhibit a small central source ($\sim$14 kpc at 1.4 GHz) with L$_{\text{1.4 GHz}}$ $\sim$6 $\cdot$ 10$^{23}$ W Hz$^{-1}$. The mean spectral index between 1.4 GHz and 5 GHz is $\sim$ -1, consistent with the usual indices found in BCGs. The cooling region extends for 40 kpc, with bolometric X-ray luminosity L$_{\text{cool}} = 1.9\pm 0.1 \cdot$ 10$^{43}$ erg s$^{-1}$. We detect an offset of $\sim$ 6 kpc between the cluster BCG and the X-ray peak, and another offset of $\sim$ 7.6 kpc between the H$α$ and the X-ray peaks. We discuss possible causes for these offsets, which suggest that the coolest gas is not condensing directly from the lowest-entropy gas. In particular, we argue that the cool ICM was drawn out from the core by sloshing, whereas the H$α$ filaments were pushed aside from the expanding radio galaxy lobes. We detect two putative X-ray cavities, spatially associated to the west radio lobe (cavity A) and to the east radio lobe (cavity B). The cavity power and age of the system are P$_{\text{cav}} \sim$ 9 $\times$10$^{42}$ erg s$^{-1}$ and t$_{\text{age}} \sim$5.2 Myr, respectively. Evaluating the position of A1668 in the cooling luminosity-cavity power parameter space, we find that the AGN energy injection is currently consistent within the scatter of the relationship, suggesting that offset cooling is likely not breaking the AGN feedback cycle.

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arXiv2020

Atacama Compact Array Measurements of the Molecular Mass in the NGC 5044 Cooling Flow Group

The fate of cooling gas in the centers of galaxy clusters and groups is still not well understood, as is also the case for the complex processes of triggering star formation in central dominant galaxies (CDGs), re-heating of cooled gas by AGN, and the triggering/feeding of supermassive black hole outbursts. We present CO observations of the early type galaxy NGC 5044, which resides at the center of an X-ray bright group with a moderate cooling flow. For our analysis we combine CO(2-1) data from the 7m antennae of the Atacama Compact Array (ACA), and the ACA total power array (TP). We demonstrate, using the 7m array data, that we can recover the total flux inferred from IRAM 30m single dish observations, which corresponds to a total molecular mass of about 4x10^7 Msun. Most of the recovered flux is blueshifted with respect to the galaxy rest frame and is extended on kpc-scales, suggesting low filling factor dispersed clouds. We find 8 concentrations of molecular gas out to a radius of 10 arcsec (1.5 kpc), which we identify with giant molecular clouds. The total molecular gas mass is more centrally concentrated than the X-ray emitting gas, but extended in the north-east/south-west direction beyond the IRAM 30m beam. We also compare the spatial extent of the molecular gas to the Halpha emission: The CO emission coincides with the very bright Halpha region in the center. We do not detect CO emission in the fainter Halpha regions. Furthermore, we find two CO absorption features spatially located at the center of the galaxy, within 5 pc projected distance of the AGN, infalling at 255 and 265 km/s relative to the AGN. This indicates that the two giant molecular clouds seen in absorption are most likely within the sphere of influence of the supermassive black hole.

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arXiv2019

Impact of AGN feedback on galaxies and their multiphase ISM across cosmic time

We present simulations of galaxy formation, based on the GADGET-3 code, in which a sub-resolution model for star formation and stellar feedback is interfaced with a new model for AGN feedback. Our sub-resolution model describes a multiphase ISM, accounting for hot and cold gas within the same resolution element: we exploit this feature to investigate the impact of coupling AGN feedback energy to the different phases of the ISM over cosmic time. Our fiducial model considers that AGN feedback energy coupling is driven by the covering factors of the hot and cold phases. We perform a suite of cosmological hydrodynamical simulations of disc galaxies ($M_{\rm halo, \, DM} \simeq 2 \cdot 10^{12}$ M$_{\odot}$, at $z=0$), to investigate: $(i)$ the effect of different ways of coupling AGN feedback energy to the multiphase ISM; $(ii)$ the impact of different prescriptions for gas accretion (i.e. only cold gas, both cold and hot gas, with the additional possibility of limiting gas accretion from cold gas with high angular momentum); $(iii)$ how different models of gas accretion and coupling of AGN feedback energy affect the coevolution of supermassive BHs and their host galaxy. We find that at least a share of the AGN feedback energy has to couple with the diffuse gas, in order to avoid an excessive growth of the BH mass. When the BH only accretes cold gas, it experiences a growth that is faster than in the case in which both cold and hot gas are accreted. If the accretion of cold gas with high angular momentum is reduced, the BH mass growth is delayed, the BH mass at $z=0$ is reduced by up to an order of magnitude, and the BH is prevented from accreting below $z \lesssim 2$, when the galaxy disc forms.

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arXiv2019

GASP XXIII: A jellyfish galaxy as an astrophysical laboratory of the baryonic cycle

With MUSE, Chandra, VLA, ALMA and UVIT data from the GASP programme we study the multiphase baryonic components in a jellyfish galaxy (JW100) with a stellar mass 3.2 X 10^{11} M_sun hosting an AGN. We present its spectacular extraplanar tails of ionized and molecular gas, UV stellar light, X-ray and radio continuum emission. This galaxy represents an excellent laboratory to study the interplay between different gas phases and star formation, and the influence of gas stripping, gas heating, and AGN. We analyze the physical origin of the emission at different wavelengths in the tail, in particular in-situ star formation (related to Halpha, CO and UV emission), synchrotron emission from relativistic electrons (producing the radio continuum) and heating of the stripped interstellar medium (ISM) (responsible for the X-ray emission). We show the similarities and differences of the spatial distributions of ionized gas, molecular gas and UV light, and argue that the mismatch on small scales (1kpc) is due to different stages of the star formation process. We present the relation Halpha--X-ray surface brightness, which is steeper for star-forming regions than for diffuse ionised gas regions with high [OI]/Halpha ratio. We propose that ISM heating due to interaction with the intracluster medium (either for mixing, thermal conduction or shocks) is responsible for the X-ray tail, the observed [OI]-excess and the lack of star formation in the northern part of the tail. We also report the tentative discovery in the tail of the most distant (and among the brightest) currently known ULX, a point-like ultraluminous X-ray source commonly originating in a binary stellar system powered either by an intermediate-mass black hole or a magnetized neutron star.

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arXiv2019

A BCG with offset cooling: is the AGN feedback cycle broken in A2495?

We present a combined radio/X-ray analysis of the poorly studied galaxy cluster Abell 2495 (z=0.07923) based on new EVLA and Chandra data. We also analyze and discuss Halpha emission and optical continuum data retrieved from the literature. We find an offset of 6 kpc between the cluster BCG (MCG+02-58-021) and the peak of the X-ray emission, suggesting that the cooling process is not taking place on the central galaxy nucleus. We propose that sloshing of the ICM could be responsible for this separation. Furthermore, we detect a second, 4 kpc offset between the peak of the Halpha emission and that of the X-ray emission. Optical images highlight the presence of a dust filament extending up to 6 kpc in the cluster BCG, and allow us to estimate a dust mass within the central 7 kpc of 1.7e+5 Msun. Exploiting the dust to gas ratio and the L_Halpha-M_mol relation, we argue that a significant amount (up to 10^9 Msun) of molecular gas should be present in the BCG of this cluster. We also investigate the presence of ICM depressions, finding two putative systems of cavities; the inner pair is characterized by t age = 18 Myr and P cav = 1.2e+43 erg/s, the outer one by t age = 53 Myr and P cav = 5.6e+42 erg/s. Their age difference appears to be consistent with the free-fall time of the central cooling gas and with the offset timescale estimated with the Halpha kinematic data, suggesting that sloshing is likely playing a key role in this environment. Furthermore, the cavities' power analysis shows that the AGN energy injection is able to sustain the feedback cycle, despite cooling being offset from the BCG nucleus.

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arXiv2018

ALMA observations of molecular clouds in three group centered elliptical galaxies: NGC 5846, NGC 4636, and NGC 5044

We present new ALMA CO(2--1) observations of two well studied group-centered elliptical galaxies: NGC~4636 and NGC~5846. In addition, we include a revised analysis of Cycle 0 ALMA observations of the central galaxy in the NGC~5044 group that has been previously published. We find evidence that molecular gas, in the form of off-center orbiting clouds, is a common presence in bright group-centered galaxies (BGG). CO line widths are $\gtrsim 10$ times broader than Galactic molecular clouds, and using the reference Milky Way $X_{CO}$, the total molecular mass ranges from as low as $2.6\times 10^5 M_\odot$ in NGC~4636 to $6.1\times 10^7 M_\odot$ in NGC~5044. With these parameters the virial parameters of the molecular structures is $\gg 1$. Complementary observations of NGC~5846 and NGC~4636 using the ALMA Compact Array (ACA) do not exhibit any detection of a CO diffuse component at the sensitivity level achieved by current exposures. The origin of the detected molecular features is still uncertain, but these ALMA observations suggest that they are the end product of the hot gas cooling process and not the result of merger events. Some of the molecular clouds are associated with dust features as revealed by HST dust extinction maps suggesting that these clouds formed from dust-enhanced cooling. The global nonlinear condensation may be triggered via the chaotic turbulent field or buoyant uplift. The large virial parameter of the molecular structures and correlation with the warm ($10^3 - 10^5 K$)/hot ($\ge10^6$) phase velocity dispersion provide evidence that they are unbound giant molecular associations drifting in the turbulent field, consistently with numerical predictions of the chaotic cold accretion process. Alternatively, the observed large CO line widths may be generated by molecular gas flowing out from cloud surfaces due to heating by the local hot gas atmosphere.

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arXiv2016

Spectral Energy Distribution Mapping of Two Elliptical Galaxies on sub-kpc scales

We use high-resolution Herschel-PACS data of 2 nearby elliptical galaxies, IC1459 & NGC2768 to characterize their dust and stellar content. IC1459 & NGC2768 have an unusually large amount of dust for elliptical galaxies (1-3 x 10^5 Msun), this dust is also not distributed along the stellar content. Using data from GALEX (ultraviolet) to PACS (far-infrared), we analyze the spectral energy distribution (SED) of these galaxies with CIGALEMC as a function of the projected position, binning images in 7.2" pixels. From this analysis, we derive maps of SED parameters, such as the metallicity, the stellar mass, the fraction of young star and the dust mass. The larger amount of dust in FIR maps seems related in our model to a larger fraction of young stars which can reach up to 4% in the dustier area. The young stellar population is fitted as a recent (~ 0.5 Gyr) short burst of star formation for both galaxies. The metallicities, which are fairly large at the center of both galaxies, decrease with the radial distance with fairly steep gradient for elliptical galaxies.

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arXiv2016

The Entire Virial Radius of the Fossil Cluster RXJ1159+5531: II. Dark Matter and Baryon Fraction

In this second paper on the entire virial region of the relaxed fossil cluster RXJ1159+5531, we present a hydrostatic analysis of the hot intracluster medium (ICM). For a model consisting of ICM, stellar mass from the central galaxy (BCG), and an NFW dark matter (DM) halo, we obtain good descriptions of the projected radial profiles of ICM emissivity and temperature. The BCG stellar mass is clearly detected with M_star/L_K = 0.61 +/- 0.11 solar, consistent with stellar population synthesis models for a Milky-Way IMF. We obtain a halo concentration, c_200 =8.4 +/- 1.0, and virial mass, M_200 = 7.9 +/- 0.6 x 10^13 M_sun. For its mass, the inferred concentration is larger than most relaxed halos produced in cosmological simulations with Planck parameters, consistent with RXJ1159+5531 forming earlier than the general halo population. The baryon fraction at r_200, f_b,200 = 0.134 +/- 0.007, is slightly below the Planck value (0.155) for the universe. When we account for the stellar baryons associated with non-central galaxies and the uncertain intracluster light, f_b,200 increases by ~0.015, consistent with the cosmic value. Performing our analysis in the context of MOND still requires a large DM fraction (85.0% +/- 2.5% at r=100 kpc) similar to that obtained using the standard Newtonian approach. The detection of a plausible stellar BCG mass component distinct from the NFW DM halo in the total gravitational potential suggests that ~10^14 M_sun represents the mass scale above which dissipation is unimportant in the formation of the central regions of galaxy clusters. (Abridged)

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arXiv2015

Mid-IR Enhanced Galaxies in the Coma & Virgo Cluster: lenticulars with a high star formation rate

We explore the properties of early-type galaxies (ETGs), including ellipticals (E) and lenticulars (S0), in rich environments such as clusters of galaxies (Virgo and Coma). The L_24/L_K distribution of ETGs in both Virgo and Coma clusters shows that some S0s have a much larger L_24/L_K ratio (0.5 to ~2 dex) than the bulk of the ETG population. This could be interpreted as an enhanced star formation rate in these lenticulars. We compare the optical colors of galaxies in these two clusters and investigate the nature of these sources with a large L24/L_K ratio by looking at their spatial distribution within the cluster, by analyzing their optical spectra and by looking at their optical colors compared to late-types. We obtain 10 Coma and 3 Virgo early-type sources with larger L24/L_K ratios than the bulk of their population. We call these sources Mid-Infrared Enhanced Galaxies (MIEGs). In Coma, they are mostly located in the South-West part of the cluster where a substructure is falling onto the main cluster. MIEGs present lower g-r color than the rest of the ETG sample, because of a blue continuum. We interpret the excess L24/L_K ratio as evidence for an enhanced star-formation induced as a consequence of their infall into the main cluster.

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arXiv2015

AGN-stimulated Cooling of Hot Gas in Elliptical Galaxies

We study the impact of relatively weak AGN feedback on the interstellar medium of intermediate and massive elliptical galaxies. We find that the AGN activity, while globally heating the ISM, naturally stimulates some degree of hot gas cooling on scales of several kpc. This process generates the persistent presence of a cold ISM phase, with mass ranging between 10$^4$ and $\gtrsim$ 5 $\times$ 10$^7$ M$_\odot$, where the latter value is appropriate for group centered, massive galaxies. Widespread cooling occurs where the ratio of cooling to free-fall time before the activation of the AGN feedback satisfies $t_{cool}/t_{ff} \lesssim 70$, that is we find a less restrictive threshold than commonly quoted in the literature. This process helps explaining the body of observations of cold gas (both ionized and neutral/molecular) in Ellipticals and, perhaps, the residual star formation detected in many early-type galaxies. The amount and distribution of the off-center cold gas vary irregularly with time. The cold ISM velocity field is irregular, initially sharing the (outflowing) turbulent hot gas motion. Typical velocity dispersions of the cold gas lie in the range 100-200 km/s. Freshly generated cold gas often forms a cold outflow and can appear kinematically misaligned with respect to the stars. We also follow the dust evolution in the hot and cold gas. We find that the internally generated cold ISM has a very low dust content, with representative values of the dust-to-gas ratio of 10$^{-4}$- 10$^{-5}$. Therefore, this cold gas can escape detection in the traditional dust-absorption maps.

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arXiv2015

The Entire Virial Radius of the Fossil Cluster RXJ1159+5531: I. Gas Properties

Previous analysis of the fossil-group/cluster RXJ1159+5531 with X-ray observations from a central Chandra pointing and an offset-North Suzaku pointing indicate a radial intracluster medium (ICM) entropy profile at the virial radius ($R_{\rm vir}$) consistent with predictions from gravity-only cosmological simulations, in contrast to other cool-core clusters. To examine the generality of these results, we present three new Suzaku observations that, in conjunction with the North pointing, provide complete azimuthal coverage out to $R_{\rm vir}$. With two new Chandra ACIS-I observations overlapping the North Suzaku pointing, we have resolved $\gtrsim$50\% of the cosmic X-ray background there. We present radial profiles of the ICM density, temperature, entropy, and pressure obtained for each of the four directions. We measure only modest azimuthal scatter in the ICM properties at $R_{\rm 200}$ between the Suzaku pointings: 7.6\% in temperature and 8.6\% in density, while the systematic errors can be significant. The temperature scatter, in particular, is lower than that studied at $R_{\rm 200}$ for a small number of other clusters observed with Suzaku. These azimuthal measurements verify that RXJ1159+5531 is a regular, highly relaxed system. The well-behaved entropy profiles we have measured for RXJ1159+5531 disfavor the weakening of the accretion shock as an explanation of the entropy flattening found in other cool-core clusters but is consistent with other explanations such as gas clumping, electron-ion non-equilibrium, non-thermal pressure support, and cosmic ray acceleration. Finally, we mention that the large-scale galaxy density distribution of RXJ1159+5531 seems to have little impact on its gas properties near $R_{\rm vir}$.

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arXiv2015

Hot gaseous atmospheres in galaxy groups and clusters are both heated and cooled by X-ray cavities

Expanding X-ray cavities observed in hot gas atmospheres of many galaxy groups and clusters generate shock waves and turbulence that are primary heating mechanisms required to avoid uninhibited radiatively cooling flows which are not observed. However, we show here that the evolution of buoyant cavities also stimulates radiative cooling of observable masses of low-temperature gas. During their early evolution, radiative cooling occurs in the wakes of buoyant cavities in two locations: in thin radial filaments parallel to the buoyant velocity and more broadly in gas compressed beneath rising cavities. Radiation from these sustained compressions removes entropy from the hot gas. Gas experiencing the largest entropy loss cools first, followed by gas with progressively less entropy loss. Most cooling occurs at late times, $\sim 10^8-10^9$ yrs, long after the X-ray cavities have disrupted and are impossible to detect. During these late times, slightly denser low entropy gas sinks slowly toward the centers of the hot atmospheres where it cools intermittently, forming clouds near the cluster center. Single cavities of energy $10^{57}-10^{58}$ ergs in the atmosphere of the NGC 5044 group create $10^8 - 10^9$ $M_{\odot}$ of cooled gas, exceeding the mass of extended molecular gas currently observed in that group. The cooled gas clouds we compute share many attributes with molecular clouds recently observed in NGC 5044 with ALMA: self-gravitationally unbound, dust-free, quasi-randomly distributed within a few kpc around the group center.

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arXiv2014

Molecular Gas in the X-ray Bright Group NGC 5044 as Revealed by ALMA

A short 30 minute ALMA observation of the early-type galaxy NGC 5044, which resides at the center of an X-ray bright group with a moderate cooling flow, has detected 24 molecular structures within the central 2.5 kpc. The masses of the molecular structures vary from 3e5 to 1e7 Mo3 and the CO(2-1) linewidths vary from 15 to 65 km/s. Given the large CO(2-1) linewidths, the observed structures are likely giant molecular associations (GMAs) and not individual molecular clouds (GMCs). Only a few of the GMAs are spatially resolved with the cycle 0 ALMA beam and the average density of these GMAs yields a GMC volume filling factor of about 15%. The observed masses of the resolved GMAs are insufficient for them to be gravitationally bound, however, the most massive GMA does contain a less massive component with a linewidth of 5.5 km/s (typical of an individual virialized GMC). We also show that the GMAs cannot be pressure confined by the hot gas. Given the observed CO(2-1) linewidths of the GMAs (i.e., the velocity dispersion of the embedded GMCs) they will likely disperse on a timescale of about 12 Myr, which is less than the central cooling time of the hot gas, so the embedded GMCs within a GMA must condense out of the hot gas at the same time and arise from local concentrations of thermally unstable parcels of hot gas. There are no indications of any disk-like molecular structures and all indications suggest that the molecular gas follows ballistic trajectories after condensing out of the thermally unstable hot gas. The 230 GHz luminosity of the central continuum source is 500 times greater than its low frequency radio luminosity and probably reflects a recent accretion event by the central supermassive black hole. The spectrum of the central continuum source also exhibits an absorption feature.

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arXiv2013

Variation of Mid and Far-IR Luminosities among Early-Type Galaxies: Relation to Stellar Metallicity and Cold Dust

The Hubble morphological sequence from early to late galaxies corresponds to an increasing rate of specific star formation. The Hubble sequence also follows a banana-shaped correlation between 24 and 70 micron luminosities, both normalized with the K-band luminosity. We show that this correlation is significantly tightened if galaxies with central AGN emission are removed, but the cosmic scatter of elliptical galaxies in both 24 and 70 micron luminosities remains significant along the correlation. We find that the 24 micron variation among ellipticals correlates with stellar metallicity, reflecting emission from hot dust in winds from asymptotic giant branch stars of varying metallicity. Infrared surface brightness variations in elliptical galaxies indicate that the K - 24 color profile is U-shaped for reasons that are unclear. In some elliptical galaxies cold interstellar dust emitting at 70 and 160 microns may arise from recent gas-rich mergers. However, we argue that most of the large range of 70 micron luminosity in elliptical galaxies is due to dust transported from galactic cores by feedback events in (currently IR-quiet) active galactic nuclei. Cooler dusty gas naturally accumulates in the cores of elliptical galaxies due to dust-cooled local stellar mass loss and may accrete onto the central black hole, releasing energy. AGN-heated gas can transport dust in cores 5-10 kpc out into the hot gas atmospheres where it radiates extended 70 micron emission but is eventually destroyed by sputtering. This, and some modest star formation, defines a cycle of dust creation and destruction. Elliptical galaxies evidently undergo large transient excursions in the banana plot in times comparable to the sputtering time or AGN duty cycle, 10 Myrs. Normally regarded as passive, elliptical galaxies are the most active galaxies in the IR color-color correlation.

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arXiv2012

Reconciling stellar dynamical and hydrostatic X-ray mass measurements of an elliptical galaxy with gas rotation, turbulence and magnetic fields

Recent hydrostatic X-ray studies of the hot interstellar medium (ISM) in early-type galaxies underestimate the gravitating mass as compared to stellar dynamics, implying modest, but significant deviations from exact hydrostatic equilibrium. We present a method for combining X-ray measurements and stellar dynamical constraints in the context of Bayesian statistics that allows the radial distribution of the implied nonthermal pressure or bulk motions in the hot ISM to be constrained. We demonstrate the accuracy of the method with hydrodynamical simulations tailored to produce a realistic galaxy model. Applying the method to the nearby elliptical galaxy NGC4649, we find a significant but subdominant nonthermal pressure fraction (0.27+/-0.06) in the central (<5 kpc) part of the galaxy, similar to the level of deviations from hydrostatic equilibrium expected in galaxy clusters. Plausible sources of systematic error, if important, may reduce this fraction. This would imply >360 km/s random turbulence or a magnetic field B=(39+/-6)(n_e/0.1 cm^{-3})^{0.59+/-0.09} muG, whereas gas rotation alone is unlikely to explain the detailed nonthermal profile. Future observations with Astro-H will allow turbulence or gas rotation at this level to be detected.

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arXiv2012

A Chandra - VLA Investigation of the X-ray Cavity System and Radio Mini-Halo in the Galaxy Cluster RBS 797

We present a study of the cavity system in the galaxy cluster RBS 797 based on Chandra and VLA data. RBS 797 (z = 0.35), is one of the most distant galaxy clusters in which two pronounced X-ray cavities have been discovered. The Chandra data confirm the presence of a cool core and indicate an higher metallicity along the cavity directions. This is likely due to the AGN outburst, which lifts cool metal-rich gas from the center along the cavities, as seen in other systems. We find indications that the cavities are hotter than the surrounding gas. Moreover, the new Chandra images show bright rims contrasting with the deep, X-ray deficient cavities. The likely cause is that the expanding 1.4 GHz radio lobes have displaced the gas, compressing it into a shell that appears as bright cool arms. Finally we show that the large-scale radio emission detected with our VLA observations may be classified as a radio mini-halo, powered by the cooling flow (CF), as it nicely follows the trend P_radio vs. P_CF predicted by the re-acceleration model.

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