Clusters of galaxies are the most massive gravitationally bound objects in the universe. Most of the baryonic matter in them is in the form of a hot and dilute plasma called the intracluster medium (ICM), which emits free-free and line emission in X-rays. The central cooling times for many clusters is much shorter than the Hubble time, yet the cluster cores do not cool catastrophically. Although it is widely accepted that AGN feedback should balance cooling (statistically) to prevent cooling flows, the details of the process are unclear. I discuss the mixing properties of the ICM plasma, which is crucial to understand isotropic heating of the ICM plasma. I will present results from simulations of the thermal instability in the ICM; thermal instability is critical to explain H_\alpha and molecular filaments observed in the cores of clusters like Perseus. I will briefly discuss the role of cosmic rays in determining dynamics (via convection) and energetics in the cluster cores. I will critically examine the different proposals to solve the cooling flow problem and stress that how the ICM is heated isotropically is still far from clear.

Future large ensembles of time delay lenses have the potential to provide interesting cosmological constraints complementary to those of other methods. Current constraints from 10-16 time delay lenses already yield the Hubble constant (h) in agreement with and to roughly the same level of precision (10%) as the HST Key Project which analyzed 40 Cepheids. Future surveys (Pan-STARRS, LSST, JDEM / IDECS, SKA, OMEGA) will yield hundreds or even thousands of lenses with well-measured time delays. We find in a flat universe with constant w including a Planck prior, LSST time delay measurements for ~4,000 lenses should constrain h to 0.007 (~1%), Omega_de to ~0.005, and w to ~0.026 (all 1-sigma precisions). Similar constraints could be obtained by a dedicated gravitational lens observatory (OMEGA) which would obtain precise time delay and mass model measurements for ~100 lenses with spectroscopic redshifts. Constraints for a general cosmology are presented as well. We compare these to the "optimistic Stage IV" constraints expected from weak lensing, supernovae, baryon acoustic oscillations, and cluster counts, as calculated by the Dark Energy Task Force. As with any method, there are systematics we must learn to control, and we discuss these issues.

Recent observational studies have discovered a tight relation between the star formation rates (SFR) and stellar masses (Mstar) of galaxies. The slope and scatter of the SFR-Mstar relation are observed to be roughly independent of redshift, whereas the zero point increases by a factor of ~20 from redshift z=0 to z~2. We use a semi-analytic galaxy evolution model to explore the origin of the zero point evolution and small scatter. We discuss whether the strong zero point evolution is driven by 1) increase in gas supply; 2) increase in gas masses; or 3) increase in gas density. We discuss whether the scatter in the SFR-Mstar relation is driven by variations in the gas supply rate, or variations in the internal structure of star forming galaxies.

There are many theories successful in explaining the observed correlations between black holes and their host galaxies. In turn, these theories play a crucial role in explaining many other observed aspects of the galaxy population. However, observational measurements of the interaction of black holes with their hosts remain scarce. I will present results on the growth of black holes in 400 local galactic bulges which have experienced a strong burst of star formation in the past 600 Myr. I will show how the processes at work in this local starburst sample may well be relevant to the co-evolution of black holes and bulges over cosmic time.

Under the LCDM paradigm, the growth of structure is the backbone for galaxy formation and evolution. Using the underlying growth of structure and normal star formation efficiencies, we build a very simple model for star-forming galaxies (SFGs). We find that SFGs form stars in a quasi-steady state at a rate set by the cosmological accretion at z < 4--6. Using this model, we study the impact of suppressing gas accretion below a mass floor. We find that this floor mass (1) helps reproducing the slopes of both the Tully-Fisher relation and the relation between star-formation rate and stellar mass; (2) introduces a mass-dependent delay in star-formation activity and naturally leads to "downsizing", where more massive halos form first on a shorter time scale. (3) accounts for the rise in the cosmic star-formation history from z = 6 to z = 2. We discuss the physical origin of the mass floor.

After the first 14 months of operations, the Fermi Gamma-Ray Space Telescope has observed over 320 GRBs, including more than 10 by the ground-breaking Large Area Telescope. As with each new capability, the new observations are re-writing the book about what we thought we knew about GRBs as well as raising new questions. In particular, the joint spectroscopy from the two instruments, covering roughly 6 decades in energy, has revealed some remarkable surprises. In particular, there are some interesting limits that can be placed on the level of violation of Lorentz Invariance by high-energy photons.

Pulsars are powerful sources of radiation across the electromagnetic spectrum. For those that emit in the gamma-ray band, dramatic advances are now being driven by the huge data infusion provided by NASA's Fermi mission, launched in mid-2008. The LAT instrument on Fermi has performed phase-resolved spectroscopy in a multitude of pulsars, some not known before to the X-ray and radio astronomy communities. This talk will summarize the key observational results and developments provided by Fermi, and highlight some consequent advances in theoretical insights into these topical lighthouses in the sky. These include the discrimination between polar cap and slot gap/outer gap acceleration zones in young and middle-aged pulsars.