Minghe Sun

Revealing the Interaction between the X-Ray Gas of Starburst Galaxy UGC 6697 and the Hot Intracluster Medium of A1367

We present the result from a Chandra observation of an X-ray-luminous starburst galaxy, UGC 6697, which is embedded in the northwest hot region of A1367 (5-6 keV). A very sharp X-ray edge (~13-fold surface brightness jump) at the southeast and a long tail (at least 60 kpc from the nucleus) at the northwest of the galaxy are detected, as expected if the galaxy is moving to the southeast. The X-ray edge, at the midway of the nucleus and the southeast optical disk edge, is also at the same position where the Hα emission is truncated and a radio sharp edge is observed. The X-ray diffuse emission is also enhanced at the southeast, implying ram pressure compression. No extraplanar X-ray component is detected, probably because of the combining effects of weaker outflow activity than that in nuclear starbursts, and external confinement plus stripping. The diffuse thermal gas in UGC 6697 has a temperature of ~0.7 keV and a low iron abundance (~0.1-0.2 solar). An X-ray point source (L0.5-10 keV ~ 2.8 × 1040 ergs s-1) is detected on the nucleus, but not highly absorbed. Three off-center ultraluminous X-ray sources, all with L0.5-10 keV > 1040 ergs s-1, are also detected. Based on the multiwavelength data available, we favor that the interaction between the interstellar medium and the intracluster medium plays a major role in triggering the starburst in UGC 6697.

THE SURVIVAL AND DESTRUCTION OF X-RAY CORONAE OF EARLY-TYPE GALAXIES IN RICH CLUSTER ENVIRONMENTS: A CASE STUDY OF A1367

A new Chandra observation of the northwest region of the galaxy cluster A1367 reveals four cool galaxy coronae (0.4-1.0 keV) embedded in the hot (5-6 keV) intracluster medium (ICM). While the large coronae of NGC 3842 and NGC 3837 appear symmetric and relaxed, the galaxy coronae of the L* galaxies (NGC 3841 and CGCG 97090) are disturbed and being stripped. Massive galaxies, generally with dense cooling cores, are better able to resist ram pressure stripping and survive in rich environments than L* galaxies, whose galactic coronae are generally much less dense. The survival of these cool coronae implies that thermal conduction from the hot surrounding ICM has to be suppressed by a factor of at least 60 at the corona boundary. Within the galaxy coronae of NGC 3842 and NGC 3837, stellar mass loss or heat conduction with the Spitzer value may be sufficient to balance radiative cooling. Energy deposition at the ends of collimated jets may heat the outer coronae but allow the survival of a small, dense gas core (e.g., NGC 3842 in A1367 and NGC 4874 in the Coma Cluster). The surviving X-ray coronae become significantly smaller and fainter with the increasing ambient pressure.

Chandra View of the Dynamically Young Cluster of Galaxies A1367. II. Point Sources

A 40 ks Chandra ACIS-S observation of the dynamically young cluster A1367 yields new insights on X-ray emission from cluster member galaxies. We detect 59 pointlike sources in the ACIS field, of which eight are identified with known cluster member galaxies. Thus, in total 10 member galaxies are detected in X-rays when three galaxies discussed in Paper I (NGC 3860 is discussed in both papers) are included. The superior spatial resolution and good spectroscopy capability of Chandra allow us to constrain the emission nature of these galaxies. Central nuclei, thermal halos, and stellar components are revealed in their spectra. Two new low-luminosity active galactic nuclei (LLAGNs) are found, including an absorbed one (NGC 3861). Besides these two for sure, two new LLAGN candidates are also found. This discovery makes the LLAGN/AGN content in this part of A1367 very high (12%). Thermal halos with temperatures around 0.5-0.8 keV are revealed in the spectra of NGC 3842 and NGC 3837, which suggests that galactic coronae can survive in clusters and that heat conduction must be suppressed. The X-ray spectrum of NGC 3862 (3C 264) resembles a BL Lac object with a photon index of ~2.5. We also present an analysis of other point sources in the field and discuss the apparent source excess (~2.5 σ) in the central field.

Shaken snow globes: kinematic tracers of the multiphase condensation cascade in massive galaxies, groups, and clusters

We propose a novel method to constrain turbulence and bulk motions in massive galaxies, groups and clusters, exploring both simulations and observations. As emerged in the recent picture of the top-down multiphase condensation, the hot gaseous halos are tightly linked to all other phases in terms of cospatiality and thermodynamics. While hot halos (10^7 K) are perturbed by subsonic turbulence, warm (10^4 K) ionized and neutral filaments condense out of the turbulent eddies. The peaks condense into cold molecular clouds (< 100 K) raining in the core via chaotic cold accretion (CCA). We show all phases are tightly linked via the ensemble (wide-aperture) velocity dispersion along the line of sight. The correlation arises in complementary long-term AGN feedback simulations and high-resolution CCA runs, and is corroborated by the combined Hitomi and new IFU measurements in Perseus cluster. The ensemble multiphase gas distributions are characterized by substantial spectral line broadening (100-200 km/s) with mild line shift. On the other hand, pencil-beam detections sample the small-scale clouds displaying smaller broadening and significant line shift up to several 100 km/s, with increased scatter due to the turbulence intermittency. We present new ensemble sigma_v of the warm Halpha+[NII] gas in 72 observed cluster/group cores: the constraints are consistent with the simulations and can be used as robust proxies for the turbulent velocities, in particular for the challenging hot plasma (otherwise requiring extremely long X-ray exposures). We show the physically motivated criterion C = t_cool/t_eddy ~ 1 best traces the condensation extent region and presence of multiphase gas in observed clusters/groups. The ensemble method can be applied to many available datasets and can substantially advance our understanding of multiphase halos in light of the next-generation multiwavelength missions.