Attila Popping (CSIRO - ATNF)

Diffuse neutral hydrogen in the Local Universe - Attila Popping Colloquium (NON-STANDARD DATE)

ATNF Marsfield Lecture Theatre

Abstract

Imaging the Local Cosmic web is essential to understand the distribution and kinematics of diffuse systems. This intergalactic regime provides a wealth of information about structure formation: e.g. tidal filaments and feedback processes such as galactic winds or AGN driven cavities. Furthermore, observations of the Cosmic Web can test our cosmological model and can demonstrate under what conditions “cold-mode” or “hot-mode” accretion dominates.

We will investigate the IGM using the HI emission line, by both exploring numerical simulations and deep observations using the WSRT and re-processed HIPASS data. Due to the moderately high temperature in the intergalactic medium of above 10^4 Kelvin, most of the gas in the Cosmic Web is highly ionised. The neutral hydrogen component covers column densities from 10^14 to 10^19 cm−2, but most of the HI will be in the Lyman Limit regime at column densities between 10^17 and 10^19 cm^−2. Although conventional imaging in the 21-cm emission line of neutral hydrogen has not typically reached column densities below about 10^19 cm−2, this is not a fundamental limitation. Long integrations with an (almost-)filled aperture can achieve much lower limits, permiting direct imaging of the Cosmic Web down to 10^17 cm^−2