A statistical characterization of the intergalactic medium in intercluster filaments

I will describe our recent survey to constrain the properties of the intergalactic medium (IGM) in the densest filaments of the cosmic web. We selected a single bright QSO whose sightline intersects 7 independent galaxy-cluster pairs at impact parameters less than 3 Mpc, and observed it with the Cosmic Origins Spectrograph (COS) on the HST. These observations directly assess the incidence of HI and OVI gas associated with these cluster-pairs. By comparing the relative incidences as a function of distance to the cluster-pair axes, our results are consistent with a filamentary structure for the absorbing gas, and also hint towards the presence of the ellusive warm-hot intergalactic medium (WHIM). Our methodology provides a viable way to constrain the properties of the gas in the densest filaments of the cosmic web, a fundamental observable to understand galaxy formation and the evolution of baryonic matter in the Universe.

Gravitational Instabilities in Kepler potentials

Closed orbits are drivers of gravitational instabilities. Kepler potentials are one of only two potentials in which bound orbits are closed. Though the Kepler potential is common in astrophysics -- relevant for stars orbiting massive black holes in the centers of galaxies, for planets orbiting stars, and for moons orbiting planets -- few instabilities have been explored beyond the linear regime in this potential. I will present two instabilities in Keplerian disks, one which which drives exponential growth in inclinations of orbiting objects and also aligns their angles of pericenter. Observations of dwarf planets in the inner Oort Cloud show evidence for this instability taking place. I will discuss predictions for the galactic center and other galactic nuclei.

Mid-Infrared Selected Dust-Rich Quasars: Recovering the Extended Quasar Population

Quasars are shining beacons in the universe that enlightens us of the path to galaxy formation and evolution. However, there is no consensus on the physics of how quasars and their host galaxies interact. The statistical properties of quasars are therefore of critical values to our understanding of how the universe evolves to its present form, and what physical processes were involved in the active galaxy evolution stage. While many quasar samples to date underlines the point-source nature of unobscured quasars, we select an isotropic quasar sample, a 'dust-rich' population, based on Spitzer MIPS flux and MMT spectroscopy. I will present the results of the study, including the recovery of a significant subgroup of extended objects, the implications on quasar-host connections, as well as ongoing efforts to study the obscuration via absorption features.

"Friday Astro Lunch Talk"

 The Puzzle of the Pluto Satellite System

The dwarf planet Pluto has a fascinating satellite system with five known members: Charon, Styx, Nix, Kerberos, and Hydra. The innermost satellite Charon is about 1/8 as massive as Pluto, and the Pluto-Charon system is in a dual synchronous state, which is the endpoint of tidal evolution. The orbits of the four small satellites are nearly circular and coplanar with Charon's orbit, with orbital periods nearly in the ratios 1:3:4:5:6. These properties suggest that the small satellites were debris from the same impact event that placed Charon in orbit and had been pushed to their current positions by being locked in orbital resonances with Charon as Charon's orbit was expanded by tidal interactions with Pluto. I will discuss the tidal evolution of Pluto-Charon and show that the placing of the small satellites at their current orbital positions by resonant transport is unlikely. I will also discuss some alternative scenarios for the origin of the small satellites.

Recent Construction and New Science from the Long Wavelength Array

Thomas Berlok

Magnetic fields and the Helium content in the intracluster medium

Understanding whether Helium can sediment to the core of galaxy clusters is important for a number of problems in cosmology and astrophysics. For example, our ignorance in the distribution of Helium leads to systematic uncertainties in estimating the density and masses of galaxy clusters. All current models addressing this question are one-dimensional, and ignore the fact that the intracluster medium is a dilute, magnetized plasma, which can effectively channel ions and electrons, leading to anisotropic transport of momentum, heat, and particle diffusion. This anisotropy can lead to a wide variety of instabilities, which could be relevant for understanding the dynamics of the heterogeneous medium. As part of my thesis work, I am shedding light on this problem, by investigating the dynamical role played by gradients in the temperature and mean molecular weight in a magnetized tenuous plasma, such as the ICM.