Publication Search Results

ID: 159438
Type: article
Authors: Vantyghem, A. N.; McNamara, B. R.; O'Dea, C. P.; Baum, S. A.; Combes, F.; Edge, A. C.; Fabian, A. C.; McDonald, Michael; Nulsen, P. E. J.; Russell, H. R.; Salomé, P.
Abstract: We present a recent Atacama Large Millimeter/submillimeter Array observation of the CO(1-0) line emission in the central galaxy of the Zw 3146 galaxy cluster (z = 0.2906). We also present updated X-ray cavity measurements from archival Chandra observations. The 5 × 10¹⁰ M_⊙ supply of molecular gas, which is confined to the central 4 kpc, is marginally resolved into three extensions that are reminiscent of the filaments observed in similar systems. No velocity structure that would be indicative of ordered motion is observed. The three molecular extensions all trail X-ray cavities, and are potentially formed from the condensation of intracluster gas lifted in the wakes of the rising bubbles. Many cycles of feedback would be required to account for the entire molecular gas reservoir. The molecular gas and continuum source are mutually offset by 2.6 kpc, with no detected line emission coincident with the continuum source. It is the molecular gas, not the continuum source, that lies at the gravitational center of the brightest cluster galaxy. As the brightest cluster galaxy contains possible tidal features, the displaced continuum source may correspond to the nucleus of a merging galaxy. We also discuss the possibility that a gravitational wave recoil following a black hole merger may account for the displacement.

ID: 156369
Type: article
Authors: Bulbul, Esra; Kraft, Ralph; Nulsen, Paul; Freyberg, Michael; Miller, Eric D.; Grant, Catherine; Bautz, Mark W.; Burrows, David N.; Allen, Steven; Eraerds, Tanja; Fioretti, Valentina; Gastaldello, Fabio; Ghirardini, Vittorio; Hall, David; Meidinger, Norbert; Molendi, Silvano; Rau, Arne; Wilkins, Dan; Wilms, Joern
Abstract: The particle-induced background of X-ray observatories is produced by galactic cosmic ray (GCR) primary protons, electrons, and He ions. Events due to direct interaction with the detector are usually removed by onboard processing. The interactions of these primary particles with the detector environment produce secondary particles that mimic X-ray events from celestial sources, and are much more difficult to identify. The filter-wheel closed data from the XMM-Newton EPIC-pn camera in small window mode (SWM) contains both the X-ray-like background events, and the events due to direct interactions with the primary particles. From this data, we demonstrate that X-ray-like background events are spatially correlated with the primary particle interaction. This result can be used to further characterize and reduce the non-X-ray background in silicon-based X-ray detectors in current and future missions. We also show that spectrum and pattern fractions of secondary particle events are different from those produced by cosmic X-rays.

ID: 157824
Type: article
Authors: Chen, Hao; Sun, Ming; Yagi, Masafumi; Bravo-Alfaro, Hector; Brinks, Elias; Kenney, Jeffrey; Combes, Francoise; Sivanandam, Suresh; Jachym, Pavel; Fossati, Matteo; Gavazzi, Giuseppe; Boselli, Alessandro; Nulsen, Paul; Sarazin, Craig; Ge, Chong; Yoshida, Michitoshi; Roediger, Elke
Abstract: Previous studies have revealed a population of galaxies in galaxy clusters with ram pressure stripped (RPS) tails of gas and embedded young stars. We observed 1.4 GHz continuum and H I emission with the Very Large Array in its B-configuration in two fields of the Coma cluster to study the radio properties of RPS galaxies. The best continuum sensitivities in the two fields are 6 and 8 µJy per 4 arcsec beam, respectively, which are 4 and 3 times deeper than those previously published. Radio continuum tails are found in 10 (8 are new) out of 20 RPS galaxies, unambiguously revealing the presence of relativistic electrons and magnetic fields in the stripped tails. Our results also hint that the tail has a steeper spectrum than the galaxy. The 1.4 GHz continuum in the tails is enhanced relative to their H α emission by a factor of ∼7 compared to the main bodies of the RPS galaxies. The 1.4 GHz continuum of the RPS galaxies is also enhanced relative to their infrared emission by a factor of ∼2 compared to star-forming galaxies. The enhancement is likely related to ram pressure and turbulence in the tail. We furthermore present H I detections in three RPS galaxies and upper limits for the other RPS galaxies. The cold gas in D100's stripped tail is dominated by molecular gas, which is likely a consequence of the high ambient pressure. No evidence of radio emission associated with ultra-diffuse galaxies is found in our data.

ID: 158588
Type: article
Authors: Juránová, A.; Werner, N.; Nulsen, Paul E. J.; Gaspari, M.; Lakhchaura, K.; Canning, R. E. A.; Donahue, M.; Hroch, F.; Voit, G. M.
Abstract: X-ray emitting atmospheres of non-rotating early-type galaxies and their connection to central active galactic nuclei have been thoroughly studied over the years. However, in systems with significant angular momentum, processes of heating and cooling are likely to proceed differently. We present an analysis of the hot atmospheres of six lenticulars and a spiral galaxy to study the effects of angular momentum on the hot gas properties. We find an alignment between the hot gas and the stellar distribution, with the ellipticity of the X-ray emission generally lower than that of the optical stellar emission, consistent with theoretical predictions for rotationally supported hot atmospheres. The entropy profiles of NGC 4382 and the massive spiral galaxy NGC 1961 are significantly shallower than the entropy distribution in other galaxies, suggesting the presence of strong heating (via outflows or compressional) in the central regions of these systems. Finally, we investigate the thermal (in)stability of the hot atmospheres via criteria such as the TI- and C-ratio, and discuss the possibility that the discs of cold gas present in these objects have condensed out of the hot atmospheres.

ID: 156376
Type: article
Authors: Liu, Wenhao; Sun, Ming; Nulsen, Paul E. J.; Worrall, Diana M.; Birkinshaw, Mark; Sarazin, Craig; Forman, William R.; Jones, Christine; Ge, Chong
Abstract: We present results from a deep (174 ks) Chandra observation of the FR-II radio galaxy 3C 220.1, the central brightest cluster galaxy (BCG) of a kT ∼ 4 keV cluster at z = 0.61. The temperature of the hot cluster medium drops from ∼5.9 to ∼3.9 keV at ∼35 kpc radius, while the temperature at smaller radii may be substantially lower. The central active galactic nucleus (AGN) outshines the whole cluster in X-rays, with a bolometric luminosity of 2.0 × 10⁴⁶ erg s^-1 (∼10 per cent of the Eddington rate). The system shows a pair of potential X-ray cavities ∼35 kpc east and west of the nucleus. The cavity power is estimated within the range of 1.0 × 10⁴⁴ and 1.7 × 10⁴⁵ erg s^-1, from different methods. The X-ray enhancements in the radio lobes could be due to inverse Compton emission, with a total 2-10 keV luminosity of ∼8.0 × 10⁴² erg s^-1. We compare 3C 220.1 with other cluster BCGs, including Cygnus A, as there are few BCGs in rich clusters hosting an FR-II galaxy. We also summarize the jet power of FR-II galaxies from different methods. The comparison suggests that the cavity power of FR-II galaxies likely underestimates the jet power. The properties of 3C 220.1 suggest that it is at the transition stage from quasar-mode feedback to radio- mode feedback.

ID: 157487
Type: article
Authors: Martz, C. G.; McNamara, B. R.; Nulsen, Paul E. J.; Vantyghem, A. N.; Gingras, M. -J; Babyk, Iu V.; Russell, H. R.; Edge, A. C.; McDonald, M.; Tamhane, P. D.; Fabian, A. C.; Hogan, M. T.
Abstract: Chandra X-ray observations are analyzed for five galaxy clusters whose atmospheric cooling times, entropy parameters, and ratios of cooling time to freefall time within the central galaxies lie below 1 Gyr, below 30 keV cm², and between 20 ≲ min(t_cool/t_ff) ≲ 50, respectively. These thermodynamic properties are commonly associated with molecular clouds, bright Hα emission, and star formation in central galaxies. However, all have Hα luminosities below 10⁴⁰ erg s^-1 in the ACCEPT database. Star formation and molecular gas are absent at the levels seen in other central galaxies with similar atmospheric properties. Only RBS 0533 may host a radio/X-ray bubble, which are commonly observed in cooling atmospheres. Signatures of uplifted, high-metallicity atmospheric gas are absent. Their atmospheres are apparently thermodynamically stable despite the absence of strong nuclear feedback. We suggest that extended filaments of nebular emission and associate molecular clouds are absent at appreciable levels because their central radio sources have failed to lift low-entropy atmospheric gas to an altitude where the ratio of the cooling time to the freefall time falls below unity and the gas becomes thermally unstable.

ID: 156460
Type: article
Authors: Snios, Bradford; Johnson, Amalya C.; Nulsen, Paul E. J.; Kraft, Ralph P.; de Vries, Martijn; Perley, Richard A.; Sebokolodi, Lerato; Wise, Michael W.
Abstract: The powerful Fanaroff-Riley class II (FR II) radio galaxy Cygnus A exhibits primary and secondary hotspots in each lobe. A 2 Ms Chandra X-ray image of Cygnus A has revealed an approximately circular hole, with a radius of 3.9 kpc, centered on the primary hotspot in the eastern radio lobe, hotspot E. We infer the distribution of X-ray emission on our line of sight from an X-ray surface brightness profile of the radio lobe adjacent to the hole and use it to argue that the hole is excavated from the radio lobe. The surface brightness profile of the hole implies a depth at least 1.7 ± 0.3 times greater than its projected width, requiring a minimum depth of 13.3 ± 2.3 kpc. A similar hole observed in the 5 GHz Very Large Array radio map reinforces the argument for a cavity lying within the lobe. We argue that the jet encounters the shock compressed intracluster medium at hotspot E, passing through one or more shocks as it is deflected back into the radio lobe. The orientation of Cygnus A allows the outflow from hotspot E to travel almost directly away from us, creating an elongated cavity, as observed. These results favor models for multiple hotspots in which an FR II jet is deflected at a primary hotspot, then travels onward to deposit the bulk of its power at a secondary hotspot, rather than the dentist drill model.

ID: 158586
Type: article
Authors: Su, Y.; Zhang, Y.; Liang, G.; ZuHone, John A.; Barnes, D. J.; Jacobs, N. B.; Ntampaka, Michelle; Forman, William R.; Nulsen, Paul E. J.; Kraft, Ralph P.; Jones, C.
Abstract: The origin of the diverse population of galaxy clusters remains an unexplained aspect of large-scale structure formation and cluster evolution. We present a novel method of using X-ray images to identify cool core (CC), weak cool core (WCC), and non-cool core (NCC) clusters of galaxies that are defined by their central cooling times. We employ a convolutional neural network, ResNet-18, which is commonly used for image analysis, to classify clusters. We produce mock Chandra X-ray observations for a sample of 318 massive clusters drawn from the IllustrisTNG simulations. The network is trained and tested with low-resolution mock Chandra images covering a central 1 Mpc square for the clusters in our sample. Without any spectral information, the deep learning algorithm is able to identify CC, WCC, and NCC clusters, achieving balanced accuracies (BAcc) of 92 per cent, 81 per cent, and 83 per cent, respectively. The performance is superior to classification by conventional methods using central gas densities, with an average ${\rm BAcc}=81{{\ \rm per\ cent}}$ , or surface brightness concentrations, giving ${\rm BAcc}=73{{\ \rm per\ cent}}$ . We use class activation mapping to localize discriminative regions for the classification decision. From this analysis, we observe that the network has utilized regions from cluster centres out to r ? 300 kpc and r ? 500 kpc to identify CC and NCC clusters, respectively. It may have recognized features in the intracluster medium that are associated with AGN feedback and disruptive major mergers.

ID: 154520
Type: article
Authors: Babyk, Iu V.; McNamara, B. R.; Tamhane, P. D.; Nulsen, P. E. J.; Russell, H. R.; Edge, A. C.
Abstract: We analyze Chandra observations of the hot atmospheres of 40 early spiral and elliptical galaxies. Using new temperature, density, cooling time, and mass profiles, we explore relationships between their hot atmospheres and cold molecular gas. Molecular gas mass correlates with atmospheric gas mass and density over four decades from central galaxies in clusters to normal giant ellipticals and early spirals. The mass and density relations follow power laws: {M}_mol}\propto {M}_{{X}}^{1.4+/- 0.1} and {M}_mol}\propto {n}_{{e}}^{1.8+/- 0.3}, respectively, at 10 kpc. The ratio of molecular gas to atmospheric gas within a 10 kpc radius lies between 3% and 10% for early-type galaxies and between 3% and 50% for central galaxies in clusters. Early-type galaxies have detectable levels of molecular gas when their atmospheric cooling times fall below ∼1 Gyr at a radius of 10 kpc. A similar trend is found in central cluster galaxies. We find no relationship between the ratio of the cooling time to free-fall time, t _c/t _ff, and the presence or absence of molecular clouds in early-type galaxies. The data are consistent with much of the molecular gas in early-type galaxies having condensed from their hot atmospheres.

ID: 155237
Type: article
Authors: Calzadilla, Michael S.; Russell, Helen R.; McDonald, Michael A.; Fabian, Andrew C.; Baum, Stefi A.; Combes, Françoise; Donahue, Megan; Edge, Alastair C.; McNamara, Brian R.; Nulsen, Paul E. J.; O'Dea, Christopher P.; Oonk, J. B. Raymond; Tremblay, Grant R.; Vantyghem, Adrian N.
Abstract: We present new, deep (245 ks) Chandra observations of the galaxy cluster Abell 1664 (z = 0.1283). These images reveal rich structure, including elongation and accompanying compressions of the X-ray isophotes in the NE-SW direction, suggesting that the hot gas is sloshing in the gravitational potential. This sloshing has resulted in cold fronts, at distances of 50, 110, and 325 kpc from the cluster center. Our results indicate that the core of A1664 is highly disturbed, as the global metallicity and cooling time flatten at small radii, implying mixing on a range of scales. The central active galactic nucleus (AGN) appears to have recently undergone a mechanical outburst, as evidenced by our detection of cavities. These cavities are the X-ray manifestations of radio bubbles inflated by the AGN and may explain the motion of cold molecular CO clouds previously observed with the Atacama Large Millimeter Array (ALMA). The estimated mechanical power of the AGN, using the minimum energy required to inflate the cavities as a proxy, is {P}_cav}=(1.1+/- 1.0)× {10}⁴⁴ erg s^-1, which may be enough to drive the molecular gas flows, and offset the cooling luminosity of the intracluster medium, at {L}_cool}=(1.53+/- 0.01)× {10}⁴⁴ erg s^-1. This mechanical power is orders of magnitude higher than the measured upper limit on the X-ray luminosity of the central AGN, suggesting that its black hole may be extremely massive and/or radiatively inefficient. We map temperature variations on the same spatial scale as the molecular gas and find that the most rapidly cooling gas is mostly coincident with the molecular gas reservoir centered on the brightest cluster galaxy's systemic velocity observed with ALMA and may be fueling cold accretion onto the central black hole.

ID: 154171
Type: article
Authors: de Vries, M. N.; Wise, M. W.; Nulsen, Paul E. J.; Siemiginowska, Aneta; Rowlinson, A.; Reynolds, C. S.
Abstract: In 2015, a radio transient named Cygnus A-2 was discovered in Cygnus A with the Very Large Array. Because of its radio brightness (νF_ν ≈ 6 × 10³⁹ erg s^-1), this transient likely represents a secondary black hole in orbit around the active galactic nucleus. Using Chandra ACIS observations from 2015 to 2017, we have looked for an X-ray counterpart to Cygnus A-2. The separation of 0.42 arcsec means that Cygnus A-2 cannot be spatially resolved, but by comparing the data with simulated MARX data, we put an upper limit to the 2-10 keV X-ray luminosity of Cygnus A-2 of 1 × 10⁴³ erg s^-1. Using the Fundamental Plane for accreting black holes, we find that our upper limit to the X-ray flux of Cygnus A-2 in 2015-2017 disfavours the interpretation of Cygnus A-2 as a steadily accreting black hole. We suggest instead that Cygnus A-2 is the radio afterglow of a tidal disruption event (TDE) and that a peak in the 2-10 keV luminosity of the nuclear region in 2013, when it was observed by Swift and NuSTAR, is X-ray emission from the TDE. A TDE could naturally explain the X-ray light curve of the nuclear region, as well as the appearance of a short-lived, fast, and ionized outflow previously detected in the 2013 NuSTAR spectrum. Both the radio and X-ray luminosities fall in between typical luminosities for `thermal' and `jetted' TDE types, suggesting that Cygnus A-2 would be unlike previously seen TDEs.

ID: 154412
Type: article
Authors: Grossová, R.; Werner, N.; Rajpurohit, K.; Mernier, F.; Lakhchaura, K.; Gabányi, K.; Canning, R. E. A.; Nulsen, Paul; Massaro, F.; Sun, M.; Connor, T.; King, A.; Allen, S. W.; Frisbie, R. L. S.; Donahue, M.; Fabian, A. C.
Abstract: We present new Karl G. Jansky Very Large Array (VLA, 1.5 GHz) radio data for the giant elliptical galaxy IC 4296, supported by archival radio, X-ray (Chandra, and XMM-Newton) and optical (SOAR, and HST) observations. The galaxy hosts powerful radio jets piercing through the inner hot X-ray emitting atmosphere, depositing most of the energy into the ambient intracluster medium (ICM). Whereas the radio surface brightness of the A configuration image is consistent with a Fanaroff- Riley Class I system, the D configuration image shows two bright, relative to the central region, large ({̃ } 160 {kpc} diameter), well- defined lobes, previously reported by Killeen et al., at a projected distance r≳ 230 {kpc}. The XMM-Newton image reveals an X-ray cavity associated with one of the radio lobes. The total enthalpy of the radio lobes is {̃ }7× 10^{59} {erg} and the mechanical power output of the jets is {̃ } 10^{44} {erg s}^{-1}. The jets are mildly curved and possibly rebrightened by the relative motion of the galaxy and the ICM. The lobes display sharp edges, suggesting the presence of bow shocks, which would indicate that they are expanding supersonically. The central entropy and cooling time of the X-ray gas are unusually low and the nucleus hosts a warm Hα + [N II] nebula and a cold molecular CO disc. Because most of the energy of the jets is deposited far from the nucleus, the atmosphere of the galaxy continues to cool, apparently feeding the central supermassive black hole and powering the jet activity.

ID: 151207
Type: article
Authors: Juráňová, A.; Werner, N.; Gaspari, M.; Lakhchaura, K.; Nulsen, Paul E. J.; Sun, M.; Canning, R. E. A.; Allen, S. W.; Simionescu, A.; Oonk, J. B. R.; Connor, T.; Donahue, M.
Abstract: The relative importance of the physical processes shaping the thermodynamics of the hot gas permeating rotating, massive early-type galaxies is expected to be different from that in non-rotating systems. Here, we report the results of the analysis of XMM-Newton data for the massive, lenticular galaxy NGC 7049. The galaxy harbours a dusty disc of cool gas and is surrounded by an extended hot X-ray emitting gaseous atmosphere with unusually high central entropy. The hot gas in the plane of rotation of the cool dusty disc has a multitemperature structure, consistent with ongoing cooling. We conclude that the rotational support of the hot gas is likely capable of altering the multiphase condensation regardless of the t_cool/t_ff ratio, which is here relatively high, ˜40. However, the measured ratio of cooling time and eddy turnover time around unity (C-ratio ≈ 1) implies significant condensation, and at the same time, the constrained ratio of rotational velocity and the velocity dispersion (turbulent Taylor number) Ta_t > 1 indicates that the condensing gas should follow non-radial orbits forming a disc instead of filaments. This is in agreement with hydrodynamical simulations of massive rotating galaxies predicting a similarly extended multiphase disc.

ID: 151204
Type: article
Authors: Liu, Wenhao; Sun, Ming; Nulsen, Paul; Clarke, Tracy; Sarazin, Craig; Forman, William; Gaspari, Massimo; Giacintucci, Simona; Lal, Dharam Vir; Edge, Tim
Abstract: We present results from the deep Chandra observation (105 ks), together with new Giant Metrewave Radio Telescope and Very Large Array data of the AGN outburst in the radio-loud galaxy group 3C 88. The system shows a prominent X-ray cavity on the eastern side with a diameter of ˜50 kpc at ˜28 kpc from the nucleus. The total enthalpy of the cavity is 3.8 × 10⁵⁸ erg and the average power required to inflate the X-ray bubble is ˜ 2.0 × 10⁴³ erg s^-1. From surface brightness profiles, we detect a shock with a Mach number of M = 1.4 ± 0.2, consistent with the value obtained from temperature jump. The shock energy is estimated to be 1.9 × 10⁵⁹ erg. The size and total enthalpy of the cavity in 3C 88 are the largest known in galaxy groups, as well as the shock energy. The eastern X-ray cavity is not aligned with the radio jet axis. This factor, combined with the radio morphology, strongly suggests jet reorientation in the last tens of million years. The bright rim and arm features surrounding the cavity show metallicity enhancement, suggesting they originated as high metallicity gas from the group centre, lifted by the rising X-ray bubbles. Our Chandra study of 3C 88 also reveals that galaxy groups with powerful radio AGN can have high cavity power, although deep X-ray observations are typically required to confirm the cavities in galaxy groups.

ID: 154551
Type: article
Authors: Russell, H. R.; McNamara, B. R.; Fabian, A. C.; Nulsen, P. E. J.; Combes, F.; Edge, A. C.; Madar, M.; Olivares, V.; Salomé, P.; Vantyghem, A. N.
Abstract: We present an analysis of new and archival ALMA observations of molecular gas in 12 central cluster galaxies. We examine emerging trends in molecular filament morphology and gas velocities to understand their origins. Molecular gas masses in these systems span 10^9 - 10^{11} M_{☉}, far more than most gas-rich galaxies. ALMA images reveal a distribution of morphologies from filamentary to disc-dominated structures. Circumnuclear discs on kiloparsec scales appear rare. In most systems, half to nearly all of the molecular gas lies in filamentary structures with masses of a few × 10^{8-10} M_{☉} that extend radially several to several tens of kpc. In nearly all cases the molecular gas velocities lie far below stellar velocity dispersions, indicating youth, transience, or both. Filament bulk velocities lie far below the galaxy's escape and free-fall speeds indicating they are bound and being decelerated. Most extended molecular filaments surround or lie beneath radio bubbles inflated by the central active galactic nuclei (AGNs). Smooth velocity gradients found along the filaments are consistent with gas flowing along streamlines surrounding these bubbles. Evidence suggests most of the molecular clouds formed from low entropy X-ray gas that became thermally unstable and cooled when lifted by the buoyant bubbles. Uplifted gas will stall and fall back to the galaxy in a circulating flow. The distribution in morphologies from filament to disc-dominated sources therefore implies slowly evolving molecular structures driven by the episodic activity of the AGNs.

ID: 155315
Type: article
Authors: Sheardown, Alex; Fish, Thomas M.; Roediger, Elke; Hunt, Matthew; Zuhone, John; Su, Yuanyuan; Kraft, Ralph P.; Nulsen, Paul; Churazov, Eugene; Forman, William; Jones, Christine; Lyskova, Natalya; Eckert, Dominique; De Grandi, Sabrina
Abstract: We show that there is a new class of gas tails-slingshot tails-that form as a subhalo (i.e., a subcluster or early-type cluster galaxy) moves away from the cluster center toward the apocenter of its orbit. These tails can point perpendicular or even opposite to the subhalo direction of motion, not tracing the recent orbital path. Thus, the observed tail direction can be misleading, and we caution against naive conclusions regarding the subhalo's direction of motion based on the tail direction. A head-tail morphology of a galaxy's or subcluster's gaseous atmosphere is usually attributed to ram pressure stripping, and the widely applied conclusion is that gas stripped tail traces the most recent orbit. However, during the slingshot tail stage, the subhalo is not being ram pressure stripped (RPS) and the tail is shaped by tidal forces more than just the ram pressure. Thus, applying a classic RPS scenario to a slingshot tail leads not only to an incorrect conclusion regarding the direction of motion but also to incorrect conclusions regarding the subhalo velocity, expected locations of shear flows, instabilities, and mixing. We describe the genesis and morphology of slingshot tails using data from binary cluster merger simulations and discuss their observable features and how to distinguish them from classic RPS tails. We identify three examples from the literature that are not RPS tails but slingshot tails and discuss other potential candidates.

ID: 154186
Type: article
Authors: Snios, Bradford; Nulsen, Paul E. J.; Kraft, Ralph P.; Cheung, C. C.; Meyer, Eileen T.; Forman, William R.; Jones, Christine; Murray, Stephen S.
Abstract: Chandra HRC observations are investigated for evidence of proper motion and brightness changes in the X-ray jet of the nearby radio galaxy M87. Using images spanning 5 yr, proper motion is measured in the X-ray knotHST-1, with a superluminal apparent speed of 6.3 ± 0.4c, or 24.1 ± 1.6mas yr^-1, and in Knot D, with a speed of 2.4 ± 0.6c. Upper limits are placed on the speeds of the remaining jet features. The X-ray knot speeds are in excellent agreement with existing measurements in the radio, optical, and ultraviolet. Comparing the X-ray results with imagesfrom the Hubble Space Telescope indicates that the X-ray and optical/UV emitting regions co-move. The X-ray knots also vary by up to 73% in brightness, whereas there is no evidence of brightness changes in the optical/UV. Using the synchrotron cooling models, we determine lower limits on magnetic field strengths of ̃ 420 μG and ̃ 230 μG for HST-1and Knot A, respectively, consistent with estimates of the equipartition fields. Together, these results lend strong support to the synchrotron cooling model for Knot HST-1, which requires that its superluminal motion reflects the speed of the relativistic bulk flow in the jet.

ID: 150527
Type: article
Authors: Snios, Bradford; Wykes, Sarka; Nulsen, Paul E. J.; Kraft, Ralph P.; Meyer, Eileen T.; Birkinshaw, Mark; Worrall, Diana M.; Hardcastle, Martin J.; Roediger, Elke; Forman, William R.; Jones, Christine
Abstract: We report results from Chandra observations analyzed for evidence of variability and proper motion in the X-ray jet of Centaurus A. Using data spanning 15 yr, collective proper motion of 11.3 ± 3.3 mas yr^‑1, or 0.68 ± 0.20c, is detected for the fainter X-ray knots and other substructure present within the jet. The three brightest knots (AX1A, AX1C, and BX2) are found to be stationary to an upper limit of 0.10c. Brightness variations up to 27% are detected for several X-ray knots in the jet. For the fading knots, BX2 and AX1C, the changes in spectral slope expected to accompany synchrotron cooling are not found, ruling it out and placing upper limits of ≃80 μG for each of their magnetic field strengths. Adiabatic expansion can account for the observed decreases in brightness. Constraints on models for the origin of the knots are established. Jet plasma overrunning an obstacle is favored as the generator of stationary knots, while moving knots are likely produced either by internal differences in jet speed or the late stages of jet interaction with nebular or cloud material.

ID: 154166
Type: article
Authors: Su, Y.; Kraft, Ralph P.; Nulsen, Paul E. J.; Jones, C.; Maccarone, T. J.; Mernier, F.; Lovisari, Lorenzo; Sheardown, A.; Randall, Scott W.; Roediger, E.; Fish, T. M.; Forman, William R.; Churazov, Eugene
Abstract: The M49 group, residing outside the virial radius of the Virgo cluster, is falling onto the cluster from the south. We report results from deep XMM-Newton mosaic observations of M49. Its hot gas temperature is 0.8 keV at the group center and rises to 1.5 keV beyond the brightest group galaxy (BGG). The group gas extends to radii of ̃300 kpc to the north and south. The observations reveal a cold front ̃20 kpc north of the BGG center and an X-ray-bright stripped tail 70 kpc long and 10 kpc wide to the southwest of the BGG. We argue that the atmosphere of the infalling group was slowed by its encounter with the Virgo cluster gas, causing the BGG to move forward subsonically relative to the group gas. We measure declining temperature and metallicity gradients along the stripped tail. The tail gas can be traced back to the cooler and enriched gas uplifted from the BGG center by buoyant bubbles, implying that active galactic nucleus outbursts may have intensified the stripping process. We extrapolate to a virial radius of 740 kpc and derive a virial mass of 4.6 × 10¹³ M _☉ for the M49 group. Its group atmosphere appears truncated and deficient when compared with isolated galaxy groups of similar temperatures. If M49 is on its first infall to Virgo, the infall region of a cluster could have profound impacts on galaxies and groups that are being accreted onto galaxy clusters. Alternatively, M49 may have already passed through Virgo once.

ID: 154268
Type: article
Authors: Su, Yuanyuan; Kimura, Tomoki; Kraft, Ralph P.; Nulsen, Paul E. J.; Gralla, Megan; Forman, William R.; Murakami, Go; Yamazaki, Atsushi; Yoshikawa, Ichiro
Abstract: Molecular cold gas and star formation have been observed at centers of cool core clusters, albeit at a level much smaller than expected from the classic cooling model. Feedback from the supermassive black hole is likely to have prevented hot gas from cooling. However, the exact cooling and heating processes are poorly understood. The missing key piece is the link between the hot gas (10⁷ K) and cold gas (10³ K). Using the extreme ultraviolet spectrometer on board Hisaki, we explore a distant galaxy cluster, RCS2 J232727.6-020437, one of the most massive cool core clusters with a cooling rate of 400 M _☉ yr^-1. We aim to detect gas at intermediate temperatures (3×10⁴ K) emitting He I α and He I β at rest wavelengths of 58.4 nm and 53.7 nm, respectively. Our target resides at z = 0.6986, for which these He I lines shift away from the absorption of the Galaxy. Our findings show that the amount of 10^4-5 K gas at the center of this cluster is smaller than expected if cooling there was uninhibited, which demonstrates that feedback both operates and is efficient for massive clusters at these epochs.