Speaker
Description
Luminous and ultra-luminous infrared galaxies (LIRGs and ULIRGs) play a crucial role in our understanding of galaxy evolution, as they represent phases of intense star formation and rapid supermassive black hole (SMBH) growth. A subset with 21 (38) per cent of the nearby (U)LIRGs shown to contain a highly obscured central galactic engine, a Compact Obscured Nuclei (CON), representing a crucial and unique phase of galaxy evolution, yet poorly constrained. The CON abundance in nearby (U)LIRGs points to a missing component in models of massive star-forming galaxies. To make matters worse, observations still are unable to exclude the origins of the warm dust these present through an abnormal mode of star-formation or through a rapidly accreting nuclear black hole.
With the unprecedented sensitivity in the infrareds capable of penetrating the high obscurations of CONs, the James Webb Space Telescope (JWST) now offers a unique chance to characterize the very smallest dust grains, the polycyclic aromatic hydrocarbons (PAHs). By spatially comparing the PAH feature ratios using JWST/NIRSpec IFU and JWST/MIRI MRS observations towards CONs IC 860 and NGC 4418 we are able to provides key constraints on both the dust grain composition and their grain size distribution in these targets. Folding in the diagnostics from ice-features such as H2O, CO2 and CO furthermore reveals dust processing effects, notably highlighting any potential shielding from the central CON. Also exploiting molecular species such as the P and Q-branches of HCN and C2H2 provides a clear view of the obscuration, all contributing to finding the nature of the still unknown powersource of the CONs.