Sthabile Kolwa – The cold CGM emerging through trace neutral carbon detections in high-z radio galaxies
May 6 @ 11:00 am - 12:00 pm
Thursday 6 May 2021
Dr Sthabile Kolwa (UJ)
The cold CGM emerging through trace neutral carbon detections in high-z radio galaxies
The ionised phase of the circumgalactic medium in high-z galaxies has been widely studied through spectroscopic observations that reveal Ly-alpha emission nebulae surrounding such galaxies. The cold phase of the CGM, however, is rather recently charted territory and within the last decade, there has been burgeoning evidence for molecular gas (H2), traced by CO lines, being found to exist within the CGM of high-z galaxies. We have therefore obtained line and continuum ALMA observations in bands 3 and 4 for seven radio galaxies at high-z (z=2.9 – 4.5), targeting the [CI] 1-0 line (νrest = 492.161 GHz) which also traces H2 to trace the cold gas component. From [CI] line emission, we have found tentative evidence for cold gas in the CGM of several host galaxies at projected distances of between 20 and 190 kpc from the nuclei and spatially coincident with the extended Ly-alpha haloes. The line detections are found to have widths of 20 – 220 km/s indicative of dynamically cold gas. In the galaxy sample, 3/7 of the host galaxies were detected in [CI] – a probable indication of molecular gas depletion in the ISM. The depletion of gas, if valid, aligns well with results from Falkendal et al 2019 who showed that high-z radio galaxies preferentially lie below the main-sequence of star-forming galaxies and, on average, have lower star-formation rates than expected for galaxies within their stellar mass range. High-z radio galaxies will be important beacons for studying radio-mode feedback with MeerKAT continuum data and later on, the SKA. Hence, understanding their star-formation properties is of utmost importance in building theory on radio galaxy evolution.