Speaker
Description
The radiative cooling time of hot gas at the centres of many cool cores in clusters of galaxies & massive elliptical galaxies is short, dropping below $10^8$ years. At the same time, the mass cooling rates inferred from simple modelling of X-ray observations of these objects are very low, indicating that either AGN feedback is tightly balanced or that the soft X-rays from cooling gas are somehow hidden from view. This Cooling Flow Problem has been extensively studied in galaxy clusters, but in our work we tackle this problem in elliptical galaxies. An intrinsic absorption model, originally developed for application to galaxy clusters (Allen & Fabian 1997), is applied to search for hidden cooling flows (HCFs) of gas in seven nearby elliptical galaxies (z~0.001-0.007). We find that intrinsic photoelectric absorption can explain the observed lack of strong soft X-ray emission from cooling flows in the spectra of elliptical galaxies. Hidden mass cooling rates of ~0.5-8 $\text{M}_{\odot} \ \text{yr}^{-1}$ are identified in each galaxy, with absorbed emission ultimately emerging in the far-infrared (FIR) band. In each galaxy, the cooling flow luminosity calculated from the inferred HCF rate was found to agree with the observed FIR luminosity. The discrepancy between calculated HCF rates and observed normal star formation rates suggests an alternative fate for the cooled gas, with low-mass star formation considered as the primary outcome.
