Day 825

Wednesday.... Monday.

1501.07647
Hot gaseous atmospheres in galaxy groups and clusters are both heated and cooled by X-ray cavities
Brighenti, Mathews, Temi

Show that the evolution of buoyant X-ray cavities, observed in hot gas atmospheres of many galaxy groups and clusters, and which generate shock waves and turbulence that are primarily heating mechanisms, 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 removed entropy form 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, ~1e8-9 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 1e57-58 ergs in the atmosphere of the NGC 5044 group create 1e8-9 Msun of cooled gas, exceeding the mass of extended molecular gas currently observed in that group.  The cooled gas clouds computed 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.

1501.07764
Flow patterns around dark matter haloes: the link between halo dynamical properties and large scale tidal field
Shi, Wang, Mo

Find that local tidal field can significantly increase the tangential component of the infall velocity, but on average do not change the radial component significantly.  These results can be used to explain how the internal velocity anisotropy and spin of haloes depend on environment.  The position vectors and velocities of infall haloes are aligned with the principal axes of the local tidal field, and the alignment depends on the strength of the tidal field.  Opposite accretion pattern are found in weak and strong tidal fields, in the sense that in a weak field the accretion flow is dominated by radial motion within the local structure, while a large tangential component is present in a strong field.  These findings can be used to understand the strong alignments found between the principal axes of the internal velocity ellipsoids of halos and the local tidal field, and their dependence on the strength of tidal field.  They also explain shy halo spin increases with the strength of local tidal field, but only in weak tidal fields does the spin-tidal field alignment follow the prediction of the tidal torque theory.  Discuss how these results may be used to understand the spins of disk galaxies and velocity structures of elliptical galaxies and their correlations with large-scale structure.

1501.07897
The whole is greater than the sum of the parts: optimizing the joint science return from LSST, Euclid and WFIRST
Jain, Spergel, Bean, ... et al

The combination of these surveys should give multi-wavelength high-resolution images of galaxies and broadband data covering much of the stellar energy spectrum.  Has potential of yielding new insights into topics ranging from the formation history of the MW to the mass of the neutrino.  Enabling the astronomy community to fully exploit this multi-instrument data set is a challenging technical task: for much of the science, need to combine the photometry across multiple wavelengths with varying spectral and spatial resolution.  Identify some of the key science enabled by the combined surveys and the key technical challenges in achieving the synergies.