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Atomic hydrogen gas is the raw material out of which stars are formed, and thus it is clearly of key importance for galaxy formation and evolution. Due to limitations of existing radio telescopes, our current knowledge of this crucial galaxy component is still limited to the local Universe, but this is about to change. The next-generation radio surveys planned for the Square Kilometre Array and its precursor facilities, such as the Australian Square Kilometre Array Pathfinder (ASKAP) in Western Australia, will usher in a new era for extragalactic studies, allowing us to measure the gas content of galaxies at cosmological distances. Although a large number of galaxies will be individually detected, the most stringent constraints on gas content of galaxies across cosmic time will come from spectral stacking of undetected sources. Briefly, this technique requires to co-add (i.e. “stack”) the radio spectra of faint, undetected sources, for which accurate positions and redshifts are known from optical surveys, and yields an estimate of the average gas content of the ensemble.

The student will build a flexible, modular, user-friendly software package to be used by the next-generation extragalactic radio surveys. The software will be tested on both available and upcoming data sets, as well as on mock catalogs generated by numerical simulations of galaxy formation and evolution. The emphasis of the first part of this project is on the computational aspect; hence a strong background in programming (especially parallel computing) is required. The second part will focus on the scientific applications, such as the determination of gas scaling relations as a function of redshift.

Schematic representation of a radio data cube (left). Spectra of galaxies at known positions and redshifts are extracted from the data cube, regardless if detected (green square and bottom spectrum on the right) or not (red square and top spectrum on the right). All the spectra extracted are aligned in velocity and co-added, yielding an estimate of the average signal of the ensemble (Fabello et al. 2011).

Schematic representation of a radio data cube (left). Spectra of galaxies at known positions and redshifts are extracted from the data cube, regardless if detected (green square and bottom spectrum on the right) or not (red square and top spectrum on the right). All the spectra extracted are aligned in velocity and co-added, yielding an estimate of the average signal of the ensemble (Fabello et al. 2011).

Associated Researchers

Dr Martin Meyer

Senior Research Fellow

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