Thesis Topic: Searches for Faint Absorption Lines in Archival ALMA Data


Thesis Supervisors:

 Tony Mroczkowski (ESO)

Eugene Churazov (MPA)


We propose novel searches in archival calibrator data from the Atacama Large Millimeter/Submillimeter Array (ALMA) for absorption by metals in the spectra of bright active galactic nuclei. For example, most of the baryonic matter in the Universe can be accounted for at high redshift, but is missing locally, and is thought to be located in the warm-hot intergalactic medium (WHIM) . Simulations show the WHIM should be located in intracluster filaments, in a warm (10^4-10^7 K), low-density (and therefore low X-ray emissivity) state below soft X-ray detection limits. While difficult to detect through emission, several isotopes of metals in the WHIM should undergo transitions detectable at millimeter wavelengths in absorption. Only now, with ALMA, have instruments reached the levels of sensitivity to test this prediction, but the challenge lies in accurate calibration and pushing the limits of ALMA’s spectral dynamic range. WHIM detection may demand spectral dynamic ranges currently beyond the systematic limits in passband calibration. This could lead to the first detection of mm-wave WHIM transitions, and the techniques developed could open a new window on cosmology, much like the Sunyaev-Zel’dovich effect has over the past decade. Note that the project will necessarily demand development of new and advanced calibration techniques in the Common Astronomy Software Applications (CASA) package, which is written in Python. The student will also test these new tools on denser environments and in other spectra where dynamic ranges > 10^5 are not required.