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Showing 1-20 of about 49 results.
Temperature profiles of hot gas in early-type galaxiesKim, Dong-WooTraynor, LiamPaggi, AlessandroO'Sullivan, EwanAnderson, CraigBurke, DouglasD'Abrusco, RaffaeleFabbiano, GiuseppinaFruscione, AntonellaLauer, JenniferMcCollough, MichaelMorgan, DouglasMossman, AmyVrtilek, SaeqaTrinchieri, GinevraDOI: info:10.1093/mnras/stz3530v. 4922095–2118
Kim, Dong-Woo, Traynor, Liam, Paggi, Alessandro, O'Sullivan, Ewan, Anderson, Craig, Burke, Douglas, D'Abrusco, Raffaele, Fabbiano, Giuseppina, Fruscione, Antonella, Lauer, Jennifer, McCollough, Michael, Morgan, Douglas, Mossman, Amy, Vrtilek, Saeqa, and Trinchieri, Ginevra. 2020. "Temperature profiles of hot gas in early-type galaxies." Monthly Notices of the Royal Astronomical Society 492:2095– 2118. https://doi.org/10.1093/mnras/stz3530
ID: 155834
Type: article
Authors: Kim, Dong-Woo; Traynor, Liam; Paggi, Alessandro; O'Sullivan, Ewan; Anderson, Craig; Burke, Douglas; D'Abrusco, Raffaele; Fabbiano, Giuseppina; Fruscione, Antonella; Lauer, Jennifer; McCollough, Michael; Morgan, Douglas; Mossman, Amy; Vrtilek, Saeqa; Trinchieri, Ginevra
Abstract: Using the data products of the Chandra Galaxy Atlas (Kim et al.), we have investigated the radial profiles of the hot gas temperature in 60 early-type galaxies (ETGs). Considering the characteristic temperature and radius of the peak, dip, and break (when scaled by the gas temperature and virial radius of each galaxy), we propose a universal temperature profile of the hot halo in ETGs. In this scheme, the hot gas temperature peaks at RMAX = 35 ± 25 kpc (or ∼0.04 RVIR) and declines both inward and outward. The temperature dips (or breaks) at RMIN (or RBREAK) = 3-5 kpc (or ∼0.006 RVIR). The mean slope between RMIN (RBREAK) and RMAX is 0.3 ± 0.1. Allowing for selection effects and observational limits, we find that the universal temperature profile can describe the temperature profiles of 72 per cent (possibly up to 82 per cent) of our ETG sample. The remaining ETGs (18 per cent) with irregular or monotonically declining profiles do not fit the universal profile and require another explanation. The temperature gradient inside RMIN (RBREAK) varies widely, indicating different degrees of additional heating at small radii. Investigating the nature of the hot core (HC with a negative gradient inside RMIN), we find that HC is most clearly visible in small galaxies. Searching for potential clues associated with stellar, active galactic nucleus (AGN) feedback, and gravitational heating, we find that HC may be related to recent star formation. But we see no clear evidence that AGN feedback and gravitational heating play any significant role for HC.
Dynamical masses of brightest cluster galaxies I: stellar velocity anisotropy and mass-to-light ratiosLoubser, S. I.Babul, A.Hoekstra, H.Bahé, Y. M.O'Sullivan, EwanDonahue, M.DOI: info:10.1093/mnras/staa1682v. 4961857–1880
Loubser, S. I., Babul, A., Hoekstra, H., Bahé, Y. M., O'Sullivan, Ewan, and Donahue, M. 2020. "Dynamical masses of brightest cluster galaxies I: stellar velocity anisotropy and mass-to-light ratios." Monthly Notices of the Royal Astronomical Society 496:1857– 1880. https://doi.org/10.1093/mnras/staa1682
ID: 157855
Type: article
Authors: Loubser, S. I.; Babul, A.; Hoekstra, H.; Bahé, Y. M.; O'Sullivan, Ewan; Donahue, M.
Abstract: We investigate the stellar and dynamical mass profiles in the centres of 25 brightest cluster galaxies (BCGs) at redshifts of 0.05 ≤ z ≤ 0.30. Our spectroscopy enables us to robustly measure the Gauss-Hermite higher order velocity moments h3 and h4, which we compare to measurements for massive early-type galaxies, and central group galaxies. We measure positive central values for h4 for all the BCGs. We derive the stellar mass-to-light ratio ( $\Upsilon _{\star \rm DYN}$ ), and velocity anisotropy (β) based on a multi-Gaussian expansion (MGE) and axisymmetric Jeans Anisotropic Methods (cylindrically and spherically aligned). We explicitly include a dark matter halo mass component, which is constrained by weak gravitational lensing measurements for these clusters. We find a strong correlation between anisotropy and velocity dispersion profile slope, with rising velocity dispersion profiles corresponding to tangential anisotropy and decreasing velocity dispersion profiles corresponding to radial anisotropy. The rising velocity dispersion profiles can also indicate a significant contribution from the intracluster light (ICL) to the total light (in projection) in the centre of the galaxy. For a small number of BCGs with rising velocity dispersion profiles, a variable stellar mass-to-light ratio can also account for the profile shape, instead of tangential anisotropy or a significant ICL contribution. We note that, for some BCGs, a variable βz(r) (from radial to tangential anisotropy) can improve the model fit to the observed kinematic profiles. The observed diversity in these properties illustrates that BCGs are not the homogeneous class of objects they are often assumed to be.
SDSS-IV MaNGA: The Nature of an Off-galaxy Ha Blob-A Multiwavelength View of Offset Cooling in a Merging Galaxy GroupPan, Hsi-AnLin, LihwaiHsieh, Bau-ChingMichalowski, Michal J.Bothwell, Matthew S.Huang, SongMoiseev, Alexei V.Oparin, DmitryO'Sullivan, EwanWorrall, Diana M.Sánchez, Sebastián F.Gwyn, StephenLaw, David R.Stark, David V.Bizyaev, DmitryLi, ChengLee, Chien-HsiuFu, HaiBelfiore, FrancescoBundy, KevinFernández-Trincado, José G.Gelfand, JosephPeirani, SébastienDOI: info:10.3847/1538-4357/abb80cv. 90316
Pan, Hsi-An, Lin, Lihwai, Hsieh, Bau-Ching, Michalowski, Michal J., Bothwell, Matthew S., Huang, Song, Moiseev, Alexei V., Oparin, Dmitry, O'Sullivan, Ewan, Worrall, Diana M., Sánchez, Sebastián F., Gwyn, Stephen, Law, David R., Stark, David V., Bizyaev, Dmitry, Li, Cheng, Lee, Chien-Hsiu, Fu, Hai, Belfiore, Francesco, Bundy, Kevin, Fernández-Trincado, José G., Gelfand, Joseph, and Peirani, Sébastien. 2020. "SDSS-IV MaNGA: The Nature of an Off-galaxy Ha Blob-A Multiwavelength View of Offset Cooling in a Merging Galaxy Group." The Astrophysical Journal 903:16. https://doi.org/10.3847/1538-4357/abb80c
ID: 158860
Type: article
Authors: Pan, Hsi-An; Lin, Lihwai; Hsieh, Bau-Ching; Michalowski, Michal J.; Bothwell, Matthew S.; Huang, Song; Moiseev, Alexei V.; Oparin, Dmitry; O'Sullivan, Ewan; Worrall, Diana M.; Sánchez, Sebastián F.; Gwyn, Stephen; Law, David R.; Stark, David V.; Bizyaev, Dmitry; Li, Cheng; Lee, Chien-Hsiu; Fu, Hai; Belfiore, Francesco; Bundy, Kevin; Fernández-Trincado, José G.; Gelfand, Joseph; Peirani, Sébastien
Abstract: Galaxies in dense environments, such as groups and clusters, experience various processes by which galaxies gain and lose gas. Using data from the SDSS-IV MaNGA survey, we previously reported the discovery of a giant (6-8 kpc in diameter) Ha blob, Totoro, about 8 kpc away from a pair of galaxies (Satsuki and Mei) residing in a galaxy group that is experiencing a group-group merger. Here, we combine interferometric 12CO(1-0) molecular gas data, new wide-field Ha, u-band data, and published X-ray data to determine the origin of the blob. Several scenarios are discussed to account for its multiwavelength properties, including (1) Ha gas being stripped from the galaxy Satsuki by ram pressure, (2) a separated low-surface-brightness galaxy, (3) gas being ejected or ionized by an active galactic nucleus (AGN), and (4) a cooling intragroup medium (IGM). Scenarios (1) and (2) are less favored by the present data. Scenario (3) is also less likely as there is no evidence for an active ongoing AGN in the host galaxy. We find that the CO (cold) and Ha (warm) gas coexist with X-ray (hot) structures; moreover, the derived cooling time is within the regime where molecular and Ha gas are expected. The coexistence of gas with different temperatures also agrees with that of cooling gas in other systems. Our multiwavelength results strongly suggest that the CO and Ha gas are the product of cooling from the IGM at its current location, i.e., cooling has occurred, and may be ongoing, well outside the host-galaxy core.
The relation between the diffuse X-ray luminosity and the radio power of the central AGN in galaxy groupsPasini, T.Brüggen, M.de Gasperin, F.Bîrzan, L.O'Sullivan, EwanFinoguenov, A.Jarvis, M.Gitti, M.Brighenti, F.Whittam, I. H.Collier, J. D.Heywood, I.Gozaliasl, G.DOI: info:10.1093/mnras/staa2049v. 4972163–2174
Pasini, T., Brüggen, M., de Gasperin, F., Bîrzan, L., O'Sullivan, Ewan, Finoguenov, A., Jarvis, M., Gitti, M., Brighenti, F., Whittam, I. H., Collier, J. D., Heywood, I., and Gozaliasl, G. 2020. "The relation between the diffuse X-ray luminosity and the radio power of the central AGN in galaxy groups." Monthly Notices of the Royal Astronomical Society 497:2163– 2174. https://doi.org/10.1093/mnras/staa2049
ID: 157825
Type: article
Authors: Pasini, T.; Brüggen, M.; de Gasperin, F.; Bîrzan, L.; O'Sullivan, Ewan; Finoguenov, A.; Jarvis, M.; Gitti, M.; Brighenti, F.; Whittam, I. H.; Collier, J. D.; Heywood, I.; Gozaliasl, G.
Abstract: Our understanding of how active galactic nucleus feedback operates in galaxy clusters has improved in recent years owing to large efforts in multiwavelength observations and hydrodynamical simulations. However, it is much less clear how feedback operates in galaxy groups, which have shallower gravitational potentials. In this work, using very deep Very Large Array and new MeerKAT observations from the MIGHTEE survey, we compiled a sample of 247 X-ray selected galaxy groups detected in the COSMOS field. We have studied the relation between the X-ray emission of the intra-group medium and the 1.4 GHz radio emission of the central radio galaxy. For comparison, we have also built a control sample of 142 galaxy clusters using ROSAT and NVSS data. We find that clusters and groups follow the same correlation between X-ray and radio emission. Large radio galaxies hosted in the centres of groups and merging clusters increase the scatter of the distribution. Using statistical tests and Monte Carlo simulations, we show that the correlation is not dominated by biases or selection effects. We also find that galaxy groups are more likely than clusters to host large radio galaxies, perhaps owing to the lower ambient gas density or a more efficient accretion mode. In these groups, radiative cooling of the intra-cluster medium could be less suppressed by active galactic nucleus heating. We conclude that the feedback processes that operate in galaxy clusters are also effective in groups.
Atacama Compact Array Measurements of the Molecular Mass in the NGC 5044 Cooling-flow GroupSchellenberger, GerritDavid, Laurence P.Vrtilek, JanO'Sullivan, EwanLim, JeremyForman, WilliamSun, MingCombes, FrancoiseSalome, PhilippeJones, ChristineGiacintucci, SimonaEdge, AlastairGastaldello, FabioTemi, PasqualeBrighenti, FabrizioBardelli, SandroDOI: info:10.3847/1538-4357/ab879cv. 89472
Schellenberger, Gerrit, David, Laurence P., Vrtilek, Jan, O'Sullivan, Ewan, Lim, Jeremy, Forman, William, Sun, Ming, Combes, Francoise, Salome, Philippe, Jones, Christine, Giacintucci, Simona, Edge, Alastair, Gastaldello, Fabio, Temi, Pasquale, Brighenti, Fabrizio, and Bardelli, Sandro. 2020. "Atacama Compact Array Measurements of the Molecular Mass in the NGC 5044 Cooling-flow Group." The Astrophysical Journal 894:72. https://doi.org/10.3847/1538-4357/ab879c
ID: 156917
Type: article
Authors: Schellenberger, Gerrit; David, Laurence P.; Vrtilek, Jan; O'Sullivan, Ewan; Lim, Jeremy; Forman, William; Sun, Ming; Combes, Francoise; Salome, Philippe; Jones, Christine; Giacintucci, Simona; Edge, Alastair; Gastaldello, Fabio; Temi, Pasquale; Brighenti, Fabrizio; Bardelli, Sandro
Abstract: 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, reheating of cooled gas by active galactic nuclei (AGN), and the triggering or "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 7 m antennae of the Atacama Compact Array (ACA) and the ACA total power array (TP). We demonstrate, using the 7 m array data, that we can recover the total flux inferred from IRAM 30 m single-dish observations, which corresponds to a total molecular mass of about 4 × 107M. Most of the recovered flux is blueshifted with respect to the galaxy rest frame and is extended on kiloparsec-scales, suggesting low filling factor dispersed clouds. We find eight concentrations of molecular gas out to a radius of 10″ (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 is extended in the northeast-southwest direction beyond the IRAM 30 m beam. We also compare the spatial extent of the molecular gas to the Hα emission: The CO emission coincides with the very bright Hα region in the center. We do not detect CO emission in the fainter Hα 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-1 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.
Chandra Early-type Galaxy AtlasKim, Dong-WooAnderson, Craig S.Burke, Douglas J.D'Abrusco, RaffaeleFabbiano, GiuseppinaFruscione, AntonellaLauer, JenniferMcCollough, MichaelMorgan, DouglasMossman, AmyO'Sullivan, EwanPaggi, AlessandroVrtilek, SaeqaTrinchieri, GinevraDOI: info:10.3847/1538-4365/ab0ca4v. 24136
Kim, Dong-Woo, Anderson, Craig S., Burke, Douglas J., D'Abrusco, Raffaele, Fabbiano, Giuseppina, Fruscione, Antonella, Lauer, Jennifer, McCollough, Michael, Morgan, Douglas, Mossman, Amy, O'Sullivan, Ewan, Paggi, Alessandro, Vrtilek, Saeqa, and Trinchieri, Ginevra. 2019. "Chandra Early-type Galaxy Atlas." The Astrophysical Journal Supplement Series 241:36. https://doi.org/10.3847/1538-4365/ab0ca4
ID: 155313
Type: article
Authors: Kim, Dong-Woo; Anderson, Craig S.; Burke, Douglas J.; D'Abrusco, Raffaele; Fabbiano, Giuseppina; Fruscione, Antonella; Lauer, Jennifer; McCollough, Michael; Morgan, Douglas; Mossman, Amy; O'Sullivan, Ewan; Paggi, Alessandro; Vrtilek, Saeqa; Trinchieri, Ginevra
Abstract: The hot interstellar medium (ISM) in early-type galaxies (ETGs) plays a crucial role in understanding their formation and evolution. The structural features of the hot gas identified by Chandra observations point to key evolutionary mechanisms, (e.g., active galactic nuclei, AGN, and stellar feedback, merging history). In our Chandra Galaxy Atlas (CGA) project, taking full advantage of the Chandra capabilities, we systematically analyzed the archival Chandra data of 70 ETGs and produced uniform data products for the hot gas properties. The primary data products are spatially resolved 2D spectral maps of the hot gas from individual galaxies. We emphasize that new features can be identified in the spectral maps that are not readily visible in the surface brightness maps. The high-level images can be viewed at the dedicated CGA website, and the CGA data products can be downloaded to compare with data at other wavelengths and to perform further analyses. Using our data products, we address a few focused science topics.
The complete local volume groups sample - III. Characteristics of group central radio galaxies in the Local UniverseKolokythas, KonstantinosO'Sullivan, EwanIntema, HuibRaychaudhury, SomakBabul, ArifGiacintucci, SimonaGitti, MyriamDOI: info:10.1093/mnras/stz2082v. 4892488–2504
Kolokythas, Konstantinos, O'Sullivan, Ewan, Intema, Huib, Raychaudhury, Somak, Babul, Arif, Giacintucci, Simona, and Gitti, Myriam. 2019. "The complete local volume groups sample - III. Characteristics of group central radio galaxies in the Local Universe." Monthly Notices of the Royal Astronomical Society 489:2488– 2504. https://doi.org/10.1093/mnras/stz2082
ID: 154714
Type: article
Authors: Kolokythas, Konstantinos; O'Sullivan, Ewan; Intema, Huib; Raychaudhury, Somak; Babul, Arif; Giacintucci, Simona; Gitti, Myriam
Abstract: Using new 610 and 235 MHz observations from the giant metrewave radio telescope (GMRT) in combination with archival GMRT and very large array (VLA) survey data, we present the radio properties of the dominant early-type galaxies in the low-richness subsample of the complete local-volume groups sample (CLoGS; 27 galaxy groups) and provide results for the radio properties of the full CLoGS sample for the first time. We find a high radio detection rate in the dominant galaxies of the low-richness subsample of 82 per cent (22/27); for the full CLoGS sample the detection rate is 87 per cent (46/53). The group-dominant galaxies exhibit a wide range of radio power, 1020-1025 W Hz-1 in the 235 and 610 MHz bands, with the majority (53 per cent) presenting point-like radio emission, 19 per cent hosting currently active radio jets, 6 per cent having remnant jets, 9 per cent being diffuse, and 13 per cent having no detected radio emission. The mean spectral index of the detected radio sources in the 235-610 MHz frequency range is found to be α _{235}^{610}̃0.68, and α _{235}^{1400}̃0.59 in the 235-1400 MHz one. In agreement with earlier studies, we find that the fraction of ultrasteep spectrum sources (α > 1.3) is ̃4 per cent, mostly dependent on the detection limit at 235 MHz. The majority of point-like systems are found to reside in dynamically young groups, whereas jet systems show no preference between spiral-rich and spiral-poor group environments. The mechanical power of the jet sources in the low-richness sample groups is estimated to be ̃1042-1044 erg s-1 with their black hole masses ranging between 2 × 108 and 5 × 109 M. We confirm previous findings that while radio jet sources tend to be associated with more massive black holes, black hole mass is not the decisive factor in determining jet activity or power.
Building a cluster: shocks, cavities, and cooling filaments in the group-group merger NGC 6338O'Sullivan, EwanSchellenberger, GerritBurke, Douglas J.Sun, MingVrtilek, Jan M.David, Laurence P.Sarazin, CraigDOI: info:10.1093/mnras/stz1711v. 4882925–2946
O'Sullivan, Ewan, Schellenberger, Gerrit, Burke, Douglas J., Sun, Ming, Vrtilek, Jan M., David, Laurence P., and Sarazin, Craig. 2019. "Building a cluster: shocks, cavities, and cooling filaments in the group-group merger NGC 6338." Monthly Notices of the Royal Astronomical Society 488:2925– 2946. https://doi.org/10.1093/mnras/stz1711
ID: 154444
Type: article
Authors: O'Sullivan, Ewan; Schellenberger, Gerrit; Burke, Douglas J.; Sun, Ming; Vrtilek, Jan M.; David, Laurence P.; Sarazin, Craig
Abstract: We present deep Chandra, XMM-Newton, Giant Metrewave Radio Telescope, and Hα observations of the group-group merger NGC 6338. X-ray imaging and spectral mapping show that as well as trailing tails of cool, enriched gas, the two cool cores are embedded in an extensive region of shock-heated gas with temperatures rising to ̃5 keV. The velocity distribution of the member galaxies show that the merger is occurring primarily along the line of sight, and we estimate that the collision has produced shocks of Mach number M = 2.3 or greater, making this one of the most violent mergers yet observed between galaxy groups. Both cool cores host potential AGN cavities and Hα nebulae, indicating rapid radiative cooling. In the southern cool core around NGC 6338, we find that the X-ray filaments associated with the Hα nebula have low entropies (2) and short cooling times (̃200-300 Myr). In the northern core, we identify an Hα cloud associated with a bar of dense, cool X-ray gas offset from the dominant galaxy. We find no evidence of current jet activity in either core. We estimate the total mass of the system and find that the product of this group-group merger will likely be a galaxy cluster.
A BCG with Offset Cooling: Is the AGN Feedback Cycle Broken in A2495?Pasini, T.Gitti, M.Brighenti, F.Temi, P.Amblard, A.Hamer, S. L.Ettori, S.O'Sullivan, EwanGastaldello, F.DOI: info:10.3847/1538-4357/ab4808v. 885111
Pasini, T., Gitti, M., Brighenti, F., Temi, P., Amblard, A., Hamer, S. L., Ettori, S., O'Sullivan, Ewan, and Gastaldello, F. 2019. "A BCG with Offset Cooling: Is the AGN Feedback Cycle Broken in A2495?." The Astrophysical Journal 885:111. https://doi.org/10.3847/1538-4357/ab4808
ID: 154588
Type: article
Authors: Pasini, T.; Gitti, M.; Brighenti, F.; Temi, P.; Amblard, A.; Hamer, S. L.; Ettori, S.; O'Sullivan, Ewan; Gastaldello, F.
Abstract: We present a combined radio/X-ray analysis of the poorly studied galaxy cluster A2495 (z = 0.07923) based on new EVLA and Chandra data. We also analyze and discuss Hα emission and optical continuum data retrieved from the literature. We find an offset of ̃6 kpc between the cluster brightest cluster galaxy (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 intracluster medium (ICM) could be responsible for this separation. Furthermore, we detect a second, ̃4 kpc offset between the peak of the Hα 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 1.7 × 105 M . Exploiting the dust-to-gas ratio and the L -M mol relation, we argue that a significant amount (up to 109 M ) 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 ̃ 1.2 × 1043 erg s-1, the outer one by t age ̃ 53 Myr and P cav ̃ 5.6 × 1042 erg s-1. Their age difference appears to be consistent with the freefall time of the central cooling gas and with the offset timescale estimated with the Hα kinematic data, suggesting that sloshing is likely playing a key role in this environment. Furthermore, the cavities' power analysis shows that the active galactic nucleus energy injection is able to sustain the feedback cycle, despite cooling being offset from the BCG nucleus.
Forming One of the Most Massive Objects in the Universe: The Quadruple Merger in Abell 1758Schellenberger, GerritDavid, LaurenceO'Sullivan, EwanVrtilek, Jan M.Haines, C. P.DOI: info:10.3847/1538-4357/ab35e4v. 88259
Schellenberger, Gerrit, David, Laurence, O'Sullivan, Ewan, Vrtilek, Jan M., and Haines, C. P. 2019. "Forming One of the Most Massive Objects in the Universe: The Quadruple Merger in Abell 1758." The Astrophysical Journal 882:59. https://doi.org/10.3847/1538-4357/ab35e4
ID: 154403
Type: article
Authors: Schellenberger, Gerrit; David, Laurence; O'Sullivan, Ewan; Vrtilek, Jan M.; Haines, C. P.
Abstract: The system A1758 is made up of two galaxy clusters, a more massive, northern cluster and a southern cluster. Both parts are undergoing major merger events at different stages. Although the mass of the merger constituents provides enough energy to produce visible shock fronts in the X-ray, none have been found to date. We present detailed temperature and abundance maps based on Chandra ACIS data and identify several candidates for shocks and cold fronts from a smoothed gradient map of the surface brightness. One candidate can be confirmed as the missing shock front in the northern cluster through X-ray spectroscopy. Nonthermal radio emission observed with the GMRT confirms the presence of radio halos in the northern and southern clusters and shows evidence for a relic in the periphery of the southern cluster. We do not find evidence for shocked gas between A1758 N and A1758 S.
The mystery of the 'Kite' radio source in Abell 2626: Insights from new Chandra observationsIgnesti, A.Gitti, M.Brunetti, G.O'Sullivan, EwanSarazin, C.Wong, K.DOI: info:10.1051/0004-6361/201731380v. 610A89
Ignesti, A., Gitti, M., Brunetti, G., O'Sullivan, Ewan, Sarazin, C., and Wong, K. 2018. "The mystery of the "Kite" radio source in Abell 2626: Insights from new Chandra observations." Astronomy and Astrophysics 610:A89. https://doi.org/10.1051/0004-6361/201731380
ID: 146171
Type: article
Authors: Ignesti, A.; Gitti, M.; Brunetti, G.; O'Sullivan, Ewan; Sarazin, C.; Wong, K.
Abstract: Context. We present the results of a new Chandra study of the galaxy cluster Abell 2626. The radio emission of the cluster shows a complex system of four symmetric arcs without known correlations with the thermal X-ray emission. The mirror symmetry of the radio arcs toward the center and the presence of two optical cores in the central galaxy suggested that they may be created by pairs of precessing radio jets powered by dual active galactic nuclei (AGNs) inside the core dominant galaxy. However, previous observations failed to observe the second jetted AGN and the spectral trend due to radiative age along the radio arcs, thus challenging this interpretation. Aim. The new Chandra observation had several scientific objectives, including the search for the second AGN that would support the jet precession model. We focus here on the detailed study of the local properties of the thermal and non-thermal emission in the proximity of the radio arcs, in order to obtain further insights into their origin.
Methods: We performed a standard data reduction of the Chandra dataset deriving the radial profiles of temperature, density, pressure and cooling time of the intra-cluster medium. We further analyzed the two-dimensional (2D) distribution of the gas temperature, discovering that the south-western junction of the radio arcs surrounds the cool core of the cluster.
Results: We studied the X-ray surface brightness and spectral profiles across the junction, finding a cold front spatially coincident with the radio arcs. This may suggest a connection between the sloshing of the thermal gas and the nature of the radio filaments, raising new scenarios for their origin. A tantalizing possibility is that the radio arcs trace the projection of a complex surface connecting the sites where electrons are most efficiently reaccelerated by the turbulence that is generated by the gas sloshing. In this case, diffuse emission embedded by the arcs and with extremely steep spectrum should be most visible at very low radio frequencies.
Disturbed Fossil Group Galaxy NGC 1132Kim, Dong-WooAnderson, CraigBurke, DougFabbiano, GiuseppinaFruscione, AntonellaLauer, JenMcCollough, MichaelMorgan, DougMossman, AmyO'Sullivan, EwanPaggi, AlessandroVrtilek, SaeqaTrinchieri, GinevraDOI: info:10.3847/1538-4357/aaa43av. 853129
Kim, Dong-Woo, Anderson, Craig, Burke, Doug, Fabbiano, Giuseppina, Fruscione, Antonella, Lauer, Jen, McCollough, Michael, Morgan, Doug, Mossman, Amy, O'Sullivan, Ewan, Paggi, Alessandro, Vrtilek, Saeqa, and Trinchieri, Ginevra. 2018. "Disturbed Fossil Group Galaxy NGC 1132." The Astrophysical Journal 853:129. https://doi.org/10.3847/1538-4357/aaa43a
ID: 145806
Type: article
Authors: Kim, Dong-Woo; Anderson, Craig; Burke, Doug; Fabbiano, Giuseppina; Fruscione, Antonella; Lauer, Jen; McCollough, Michael; Morgan, Doug; Mossman, Amy; O'Sullivan, Ewan; Paggi, Alessandro; Vrtilek, Saeqa; Trinchieri, Ginevra
Abstract: We have analyzed the Chandra archival data of NGC 1132, a well-known fossil group, i.e., a system expected to be old and relaxed long after the giant elliptical galaxy assembly. Instead, the Chandra data reveal that the hot gas morphology is disturbed and asymmetrical, with a cold front following a possible bow shock. We discuss possible origins of the disturbed hot halo, including sloshing by a nearby object, merger, ram pressure by external hotter gas, and nuclear outburst. We consider that the first two mechanisms are likely explanations for the disturbed hot halo, with a slight preference for a minor merger with a low impact parameter because of the match with simulations and previous optical observations. In this case, NGC 1132 may be a rare example of unusual late mergers seen in recent simulations. Regardless of the origin of the disturbed hot halo, the paradigm of the fossil system needs to be reconsidered.
The Complete Local-volume Groups Sample - II. A study of the central radio galaxies in the high-richness sub-sampleKolokythas, KonstantinosO'Sullivan, EwanRaychaudhury, SomakGiacintucci, SimonaGitti, MyriamBabul, ArifDOI: info:10.1093/mnras/sty2030v. 4811550–1577
Kolokythas, Konstantinos, O'Sullivan, Ewan, Raychaudhury, Somak, Giacintucci, Simona, Gitti, Myriam, and Babul, Arif. 2018. "The Complete Local-volume Groups Sample - II. A study of the central radio galaxies in the high-richness sub-sample." Monthly Notices of the Royal Astronomical Society 481:1550– 1577. https://doi.org/10.1093/mnras/sty2030
ID: 150202
Type: article
Authors: Kolokythas, Konstantinos; O'Sullivan, Ewan; Raychaudhury, Somak; Giacintucci, Simona; Gitti, Myriam; Babul, Arif
Abstract: We present a study of the radio properties of the dominant early-type galaxies in 26 galaxy groups, the high-richness sub-sample of the Complete Local-volume Groups Sample (CLoGS). Combining new 610 and 235 MHz observations of 21 groups from the Giant Metrewave Radio Telescope (GMRT) with archival GMRT and Very Large Array (VLA) survey data, we find a high detection rate, with 92 per cent of the dominant galaxies hosting radio sources. The sources have a wide range of luminosities, 1020-1024 W Hz-1 in the 235 and 610 MHz bands. The majority (54 per cent) are point-like, but 23 per cent have radio jets, and another 15 per cent are diffuse radio sources with no clear jet/lobe morphology. Star formation may dominate the radio emission in 2 of the point-like systems and may make a significant contribution to a further 1-3, but is unlikely to be important in the remaining 21 galaxies. The spectral index of the detected radio sources ranges from very flat values of ˜0.2 to typical radio synchrotron spectra of ˜0.9 with only two presenting steep radio spectra with α _{235}^{610}> 1. We find that jet sources are more common in X-ray bright groups, with radio non-detections found only in X-ray faint systems. Radio point sources appear in all group environments irrespective of their X-ray properties or spiral fraction. We estimate the mechanical power (Pcav) of the jet sources in the X-ray bright groups to be 1041-1043 erg s-1, with the two large-scale jet systems (NGC 193 and NGC 4261) showing jet powers two orders of magnitude greater than the radiative losses from the cool cores of their groups. This suggests that central AGN are not always in balance with cooling, but may instead produce powerful periodical bursts of feedback heating.
Cold gas in a complete sample of group-dominant early-type galaxiesO'Sullivan, Ewan J.Combes, F.Salomé, P.David, L. P.Babul, A.Vrtilek, Jan M.Lim, J.Olivares, V.Raychaudhury, S.Schellenberger, GerritDOI: info:10.1051/0004-6361/201833580v. 618A126
O'Sullivan, Ewan J., Combes, F., Salomé, P., David, L. P., Babul, A., Vrtilek, Jan M., Lim, J., Olivares, V., Raychaudhury, S., and Schellenberger, Gerrit. 2018. "Cold gas in a complete sample of group-dominant early-type galaxies." Astronomy and Astrophysics 618:A126. https://doi.org/10.1051/0004-6361/201833580
ID: 149411
Type: article
Authors: O'Sullivan, Ewan J.; Combes, F.; Salomé, P.; David, L. P.; Babul, A.; Vrtilek, Jan M.; Lim, J.; Olivares, V.; Raychaudhury, S.; Schellenberger, Gerrit
Abstract: We present IRAM 30 m and APEX telescope observations of CO(1-0) and CO(2-1) lines in 36 group-dominant early-type galaxies, completing our molecular gas survey of dominant galaxies in the Complete Local-volume Groups Sample. We detect CO emission in 12 of the galaxies at > 4σ significance, with molecular gas masses in the range ˜ 0.01 - 6 × 108 M, as well as CO in absorption in the non-dominant group member galaxy NGC 5354. In total 21 of the 53 CLoGS dominant galaxies are detected in CO and we confirm our previous findings that they have low star formation rates (0.01-1 Myr-1) but short depletion times (>1 Gyr) implying rapid replenishment of their gas reservoirs. Comparing molecular gas mass with radio luminosity, we find that a much higher fraction of our group-dominant galaxies (60 ± 16%) are AGN-dominated than is the case for the general population of ellipticals, but that there is no clear connection between radio luminosity and the molecular gas mass. Using data from the literature, we find that at least 27 of the 53 CLoGS dominant galaxies contain H I, comparable to the fraction of nearby non-cluster early type galaxies detected in H I and significantly higher that the fraction in the Virgo cluster. We see no correlation between the presence of an X-ray detected intra-group medium and molecular gas in the dominant galaxy, but find that the H I-richest galaxies are located in X-ray faint groups. Morphological data from the literature suggests the cold gas component most commonly takes the form of a disk, but many systems show evidence of galaxy-galaxy interactions, indicating that they may have acquired their gas through stripping or mergers. We provide improved molecular gas mass estimates for two galaxies previously identified as being in the centres of cooling flows, NGC 4636 and NGC 5846, and find that they are relatively molecular gas poor compared to our other detected systems. Based on observations carried out with the IRAM 30m telescope and the Atacama Pathfinder Experiment (APEX). IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). APEX is a collaboration between the Max-Planck-Institut fur Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory.The reduced spectra are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr(ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/618/A126
The origin of the X-ray, radio and H I structures in the NGC 5903 galaxy groupO'Sullivan, EwanKolokythas, KonstantinosKantharia, Nimisha G.Raychaudhury, SomakDavid, Laurence P.Vrtilek, Jan M.DOI: info:10.1093/mnras/stx2702v. 4735248–5266
O'Sullivan, Ewan, Kolokythas, Konstantinos, Kantharia, Nimisha G., Raychaudhury, Somak, David, Laurence P., and Vrtilek, Jan M. 2018. "The origin of the X-ray, radio and H I structures in the NGC 5903 galaxy group." Monthly Notices of the Royal Astronomical Society 473:5248– 5266. https://doi.org/10.1093/mnras/stx2702
ID: 145789
Type: article
Authors: O'Sullivan, Ewan; Kolokythas, Konstantinos; Kantharia, Nimisha G.; Raychaudhury, Somak; David, Laurence P.; Vrtilek, Jan M.
Abstract: The NGC 5903 galaxy group is a nearby (∼30 Mpc) system of ∼30 members, dominated by the giant ellipticals NGC 5903 and NGC 5898. The group contains two unusual structures: a ∼110 kpc long H I filament crossing NGC 5903 and a ∼75 kpc wide diffuse, steep-spectrum radio source of unknown origin that overlaps NGC 5903 and appears to be partly enclosed by the H I filament. Using a combination of Chandra, XMM-Newton, Giant Meterwave Radio Telescope (GMRT) and Very Large Array (VLA) observations, we detect a previously unknown ∼0.65 keV intra-group medium filling the volume within 145 kpc of NGC 5903 and find a loop of enhanced X-ray emission extending ∼35 kpc south-west from the galaxy, enclosing the brightest part of the radio source. The northern and eastern parts of this X-ray structure are also strongly correlated with the southern parts of the H I filament. We determine the spectral index of the bright radio emission to be α _{150}^{612} = 1.03 ± 0.08, indicating a radiative age >360 Myr. We discuss the origin of the correlated radio, X-ray and H I structures, either through an interaction-triggered active galactic nucleus (AGN) outburst with enthalpy 1.8 × 1057 erg, or via a high-velocity collision between a galaxy and the H I filament. While neither scenario provides a complete explanation, we find that an AGN outburst is the most likely source of the principal X-ray and radio structures. However, it is clear that galaxy interactions continue to play an important role in the development of this relatively highly evolved galaxy group. We also resolve the question of whether the group member galaxy ESO 514-3 hosts a double-lobed radio source, confirming that the source is a superposed background AGN.
An Enigmatic Population of Luminous Globular Clusters in a Galaxy Lacking Dark Mattervan Dokkum, PieterCohen, YotamDanieli, ShanyKruijssen, J. M. DiederikRomanowsky, Aaron J.Merritt, AllisonAbraham, RobertoBrodie, JeanConroy, CharlieLokhorst, DeborahMowla, LamiyaO'Sullivan, EwanZhang, JielaiDOI: info:10.3847/2041-8213/aab60bv. 856L30
van Dokkum, Pieter, Cohen, Yotam, Danieli, Shany, Kruijssen, J. M. Diederik, Romanowsky, Aaron J., Merritt, Allison, Abraham, Roberto, Brodie, Jean, Conroy, Charlie, Lokhorst, Deborah, Mowla, Lamiya, O'Sullivan, Ewan, and Zhang, Jielai. 2018. "An Enigmatic Population of Luminous Globular Clusters in a Galaxy Lacking Dark Matter." Astrophysical Journal Letters 856:L30. https://doi.org/10.3847/2041-8213/aab60b
ID: 147072
Type: article
Authors: van Dokkum, Pieter; Cohen, Yotam; Danieli, Shany; Kruijssen, J. M. Diederik; Romanowsky, Aaron J.; Merritt, Allison; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Lokhorst, Deborah; Mowla, Lamiya; O'Sullivan, Ewan; Zhang, Jielai
Abstract: We recently found an ultra diffuse galaxy (UDG) with a half-light radius of R e = 2.2 kpc and little or no dark matter. The total mass of NGC1052--DF2 was measured from the radial velocities of bright compact objects that are associated with the galaxy. Here, we analyze these objects using a combination of Hubble Space Telescope (HST) imaging and Keck spectroscopy. Their average size is = 2.2 kpc and little or no dark matter. The total mass of NGC1052--DF2 was measured from the radial velocities of bright compact objects that are associated with the galaxy. Here, we analyze these objects using a combination of Hubble Space Telescope (HST) imaging and Keck spectroscopy. Their average size is h> =6.2+/- 0.5 pc and their average ellipticity is =0.18+/- 0.02. From a stacked Keck spectrum we derive an age of ≳9 Gyr and a metallicity of [Fe/H] = -1.35 ± 0.12. Their properties are similar to omega Centauri, the brightest and largest globular cluster in the Milky Way, and our results demonstrate that the luminosity function of metal-poor globular clusters is not universal. The fraction of the total stellar mass that is in the globular cluster system is similar to that in other UDGs, and consistent with ``failed galaxy'' scenarios, where star formation terminated shortly after the clusters were formed. However, the galaxy is a factor of ~1000 removed from the relation between globular cluster mass and total galaxy mass that has been found for other galaxies, including other UDGs. We infer that a dark matter halo is not a prerequisite for the formation of metal-poor globular cluster-like objects in high-redshift galaxies.
A galaxy lacking dark mattervan Dokkum, PieterDanieli, ShanyCohen, YotamMerritt, AllisonRomanowsky, Aaron J.Abraham, RobertoBrodie, JeanConroy, CharlieLokhorst, DeborahMowla, LamiyaO'Sullivan, EwanZhang, JielaiDOI: info:10.1038/nature25767v. 555629–632
van Dokkum, Pieter, Danieli, Shany, Cohen, Yotam, Merritt, Allison, Romanowsky, Aaron J., Abraham, Roberto, Brodie, Jean, Conroy, Charlie, Lokhorst, Deborah, Mowla, Lamiya, O'Sullivan, Ewan, and Zhang, Jielai. 2018. "A galaxy lacking dark matter." Nature 555:629– 632. https://doi.org/10.1038/nature25767
ID: 146131
Type: article
Authors: van Dokkum, Pieter; Danieli, Shany; Cohen, Yotam; Merritt, Allison; Romanowsky, Aaron J.; Abraham, Roberto; Brodie, Jean; Conroy, Charlie; Lokhorst, Deborah; Mowla, Lamiya; O'Sullivan, Ewan; Zhang, Jielai
Abstract: Studies of galaxy surveys in the context of the cold dark matter paradigm have shown that the mass of the dark matter halo and the total stellar mass are coupled through a function that varies smoothly with mass. Their average ratio Mhalo/Mstars has a minimum of about 30 for galaxies with stellar masses near that of the Milky Way (approximately 5 × 1010 solar masses) and increases both towards lower masses and towards higher masses. The scatter in this relation is not well known; it is generally thought to be less than a factor of two for massive galaxies but much larger for dwarf galaxies. Here we report the radial velocities of ten luminous globular-cluster-like objects in the ultra-diffuse galaxy NGC1052–DF2, which has a stellar mass of approximately 2 × 108 solar masses. We infer that its velocity dispersion is less than 10.5 kilometres per second with 90 per cent confidence, and we determine from this that its total mass within a radius of 7.6 kiloparsecs is less than 3.4 × 108 solar masses. This implies that the ratio Mhalo/Mstars is of order unity (and consistent with zero), a factor of at least 400 lower than expected. NGC1052–DF2 demonstrates that dark matter is not always coupled with baryonic matter on galactic scales.
The Presence of Thermally Unstable X-Ray Filaments and the Production of Cold Gas in the NGC 5044 GroupDavid, Laurence P.Vrtilek, JanO'Sullivan, EwanJones, ChristineForman, WilliamSun, MingDOI: info:10.3847/1538-4357/aa756cv. 84284
David, Laurence P., Vrtilek, Jan, O'Sullivan, Ewan, Jones, Christine, Forman, William, and Sun, Ming. 2017. "The Presence of Thermally Unstable X-Ray Filaments and the Production of Cold Gas in the NGC 5044 Group." The Astrophysical Journal 842:84. https://doi.org/10.3847/1538-4357/aa756c
ID: 143363
Type: article
Authors: David, Laurence P.; Vrtilek, Jan; O'Sullivan, Ewan; Jones, Christine; Forman, William; Sun, Ming
Abstract: We present the results of a deep Chandra observation of the X-ray bright moderate-cooling flow group NGC 5044 along with the observed correlations between the ionized, atomic, and molecular gas in this system. The Chandra observation shows that the central AGN has undergone two outbursts in the past 108 years, based on the presence of two pairs of nearly bipolar X-ray cavities. The molecular gas and dust within the central 2 kpc is aligned with the orientation of the inner pair of bipolar X-ray cavities, suggesting that the most recent AGN outburst had a dynamical impact on the molecular gas. NGC 5044 also hosts many X-ray filaments within the central 8 kpc, but there are no obvious connections between the X-ray and Hα filaments and the more extended X-ray cavities that were inflated during the prior AGN outburst. Using the line width of the blended Fe-L line complex as a diagnostic for multiphase gas, we find that the majority of the multiphase thermally unstable gas in NGC 5044 is confined within the X-ray filaments. While the cooling time and entropy of the gas within the X-ray filaments are very similar, not all filaments show evidence of gas cooling or an association with Hα emission. We suggest that the various observed properties of the X-ray filaments are suggestive of an evolutionary sequence where thermally unstable gas begins to cool, becomes multiphased, develops Hα emitting plasma, and finally produces cold gas.
The Complete Local Volume Groups Sample - I. Sample selection and X-ray properties of the high-richness subsampleO'Sullivan, EwanPonman, Trevor J.Kolokythas, KonstantinosRaychaudhury, SomakBabul, ArifVrtilek, Jan M.David, Laurence P.Giacintucci, SimonaGitti, MyriamHaines, Chris P.DOI: info:10.1093/mnras/stx2078v. 4721482–1505
O'Sullivan, Ewan, Ponman, Trevor J., Kolokythas, Konstantinos, Raychaudhury, Somak, Babul, Arif, Vrtilek, Jan M., David, Laurence P., Giacintucci, Simona, Gitti, Myriam, and Haines, Chris P. 2017. "The Complete Local Volume Groups Sample - I. Sample selection and X-ray properties of the high-richness subsample." Monthly Notices of the Royal Astronomical Society 472:1482– 1505. https://doi.org/10.1093/mnras/stx2078
ID: 145637
Type: article
Authors: O'Sullivan, Ewan; Ponman, Trevor J.; Kolokythas, Konstantinos; Raychaudhury, Somak; Babul, Arif; Vrtilek, Jan M.; David, Laurence P.; Giacintucci, Simona; Gitti, Myriam; Haines, Chris P.
Abstract: We present the Complete Local-Volume Groups Sample (CLoGS), a statistically complete optically selected sample of 53 groups within 80 Mpc. Our goal is to combine X-ray, radio and optical data to investigate the relationship between member galaxies, their active nuclei and the hot intra-group medium (IGM). We describe sample selection, define a 26-group high-richness subsample of groups containing at least four optically bright (log LB ≥ 10.2 LB⊙) galaxies, and report the results of XMM-Newton and Chandra observations of these systems. We find that 14 of the 26 groups are X-ray bright, possessing a group-scale IGM extending at least 65 kpc and with luminosity >1041 erg s-1, while a further three groups host smaller galaxy-scale gas haloes. The X-ray bright groups have masses in the range M500 ≃ 0.5-5 × 1013 M, based on system temperatures of 0.4-1.4 keV, and X-ray luminosities in the range 2-200 × 1041 erg s-1. We find that ∼53-65 per cent of the X-ray bright groups have cool cores, a somewhat lower fraction than found by previous archival surveys. Approximately 30 per cent of the X-ray bright groups show evidence of recent dynamical interactions (mergers or sloshing), and ∼35 per cent of their dominant early-type galaxies host active galactic nuclei with radio jets. We find no groups with unusually high central entropies, as predicted by some simulations, and confirm that CLoGS is in principle capable of detecting such systems. We identify three previously unrecognized groups, and find that they are either faint (LX, R500 42 erg s-1) with no concentrated cool core, or highly disturbed. This leads us to suggest that ∼20 per cent of X-ray bright groups in the local universe may still be unidentified.
Constraining the Physical State of the Hot Gas Halos in NGC 4649 and NGC 5846Paggi, AlessandroKim, Dong-WooAnderson, CraigBurke, DougD'Abrusco, RaffaeleFabbiano, GiuseppinaFruscione, AntonellaGokas, TaraLauer, JenMcCollough, MichaelMorgan, DougMossman, AmyO'Sullivan, EwanTrinchieri, GinevraVrtilek, SaeqaPellegrini, SilviaRomanowsky, Aaron J.Brodie, JeanDOI: info:10.3847/1538-4357/aa7897v. 8445
Paggi, Alessandro, Kim, Dong-Woo, Anderson, Craig, Burke, Doug, D'Abrusco, Raffaele, Fabbiano, Giuseppina, Fruscione, Antonella, Gokas, Tara, Lauer, Jen, McCollough, Michael, Morgan, Doug, Mossman, Amy, O'Sullivan, Ewan, Trinchieri, Ginevra, Vrtilek, Saeqa, Pellegrini, Silvia, Romanowsky, Aaron J., and Brodie, Jean. 2017. "Constraining the Physical State of the Hot Gas Halos in NGC 4649 and NGC 5846." The Astrophysical Journal 844:5. https://doi.org/10.3847/1538-4357/aa7897
ID: 143804
Type: article
Authors: Paggi, Alessandro; Kim, Dong-Woo; Anderson, Craig; Burke, Doug; D'Abrusco, Raffaele; Fabbiano, Giuseppina; Fruscione, Antonella; Gokas, Tara; Lauer, Jen; McCollough, Michael; Morgan, Doug; Mossman, Amy; O'Sullivan, Ewan; Trinchieri, Ginevra; Vrtilek, Saeqa; Pellegrini, Silvia; Romanowsky, Aaron J.; Brodie, Jean
Abstract: We present results of a joint Chandra/XMM-Newton analysis of the early-type galaxies NGC 4649 and NGC 5846 aimed at investigating differences between mass profiles derived from X-ray data and those from optical data, to probe the state of the hot interstellar medium (ISM) in these galaxies. If the hot ISM is at a given radius in hydrostatic equilibrium (HE), the X-ray data can be used to measure the total enclosed mass of the galaxy. Differences from optically derived mass distributions therefore yield information about departures from HE in the hot halos. The X-ray mass profiles in different angular sectors of NGC 4649 are generally smooth with no significant azimuthal asymmetries within 12 kpc. Extrapolation of these profiles beyond this scale yields results consistent with the optical estimate. However, in the central region (r< 3 kpc) the X-ray data underpredict the enclosed mass, when compared with the optical mass profiles. Consistent with previous results, we estimate a nonthermal pressure component accounting for 30% of the gas pressure, likely linked to nuclear activity. In NGC 5846 the X-ray mass profiles show significant azimuthal asymmetries, especially in the NE direction. Comparison with optical mass profiles in this direction suggests significant departures from HE, consistent with bulk gas compression and decompression due to sloshing on ˜15 kpc scales; this effect disappears in the NW direction, where the emission is smooth and extended. In this sector we find consistent X-ray and optical mass profiles, suggesting that the hot halo is not responding to strong nongravitational forces.