Intensity Mapping with Carbon Monoxide Emission Lines and the Redshifted 21 cm Line

We quantify the prospects for using emission lines from rotational transitions of the CO molecule to perform an `intensity mapping observation at high redshift during the Epoch of Reionization (EoR). The aim of CO intensity mapping is to observe the combined CO emission from many unresolved galaxies, to measure the spatial fluctuations in this emission, and use this as a tracer of large scale structure at very early times in the history of our Universe. This measurement would help determine the properties of molecular clouds -- the sites of star formation -- in the very galaxies that reionize the Universe. We further consider the possibility of cross-correlating CO intensity maps with future observations of the redshifted 21 cm line. The cross spectrum is less sensitive to foreground contamination than the auto power spectra, and can therefore help confirm the high redshift origin of each signal. Furthermore, the cross spectrum measurement would help extract key information about the EoR, especially regarding the size distribution of ionized regions. We discuss uncertainties in predicting the CO signal at high redshift, and discuss strategies for improving these predictions. Under favorable assumptions, and feasible specifications for a CO survey mapping the CO(2-1) and CO(1-0) lines, the power spectrum of CO emission fluctuations and its cross spectrum with future 21 cm measurements from the MWA are detectable at high significance.

Shaken and stirred: conduction and turbulence in clusters of galaxies

(abridged) Uninhibited radiative cooling in clusters of galaxies would lead to excessive mass accretion rates contrary to observations. One of the key proposals to offset radiative energy losses is thermal conduction from outer, hotter layers of cool core clusters to their centers. However, conduction is sensitive to magnetic field topology. In cool-core clusters the heat buoyancy instability (HBI) leads to B-fields ordered preferentially in the direction perpendicular to that of gravity, which significantly reduces the level of conduction below the classical Spitzer-Braginskii value. However, the cluster cool cores are rarely in perfect hydrostatic equilibrium. Sloshing motions due to minor mergers, galaxy motions or AGN can significantly perturb the gas and affect the level of thermal conduction. We perform 3D AMR MHD simulations of the effect of turbulence on the properties of the anisotropic thermal conduction in cool core clusters. We show that very weak subsonic motions, well within observational constraints, can randomize the magnetic field and significantly boost effective thermal conduction beyond the saturated values expected in the pure unperturbed HBI case. We find that the turbulent motions can essentially restore the conductive heat flow to the cool core to level comparable to the theoretical maximum of 1/3 Spitzer for a highly tangled field. Runs with radiative cooling show that the cooling catastrophe can be averted and the cluster core stabilized. Above a critical Froude number, these same turbulent motions also eliminate the tangential bias in the velocity and magnetic field that is otherwise induced by the trapped g-modes. Our results can be tested with future radio polarization measurements, and have implications for efficient metal dispersal in clusters.

Photo-heating and the fate of hard photons during the reionisation of HeII by quasars

We use a combination of analytic and numerical arguments to consider the impact of quasar photo-heating during HeII reionisation on the thermal evolution of the intergalactic medium (IGM). We demonstrate that rapid (Delta z< 0.1-0.2), strong (Delta T > 10^4 K) photo-heating is difficult to achieve across the entire IGM unless quasar spectra are significantly harder than implied by current observational constraints. Although filtering of intrinsic quasar radiation through dense regions in the IGM does increase the mean excess energy per HeII photo-ionisation, it also weakens the radiation intensity and lowers the photo-ionisation rate, preventing rapid heating over time intervals shorter than the local photo-ionisation timescale. Moreover, the hard photons responsible for the strongest heating are more likely to deposit their energy inside dense clumps. The abundance of such clumps is, however, uncertain and model-dependent, leading to a fairly large uncertainty in the photo-heating rates. Nevertheless, although some of the IGM may be exposed to a hardened and weakened ionising background for long periods, most of the IGM must instead be reionised by the more abundant, softer photons and with accordingly modest heating rates (Delta T < 10^4 K). The repeated ionisation of fossil quasar HeIII regions does not increase the net heating because the recombination times in these regions typically exceed the IGM cooling times and the average time lag between successive rounds of quasar activity. Detailed line-of-sight radiative transfer simulations confirm these expectations and predict a rich thermal structure in the IGM during HeII reionisation. [Abridged]