Unveiling Sizes of Compact AGN Hosts with ALMA

We present rest-frame far-infrared (FIR) and optical size measurements of AGN hosts and star-forming galaxies in the COSMOS field, enabled by high-resolution ALMA/1 mm and HST/F814W imaging. The sizes and SFR surface densities measured from both ALMA and HST images show that obscured AGN host galaxies are more compact than non-AGN star-forming galaxies at similar redshift and stellar mass. Moreover, most of the rest-frame FIR sizes of AGNs in our sample are similar or more compact than their rest-frame optical sizes. This result suggests that obscured accretion may compact galaxy gaseous components, linked to enhanced star formation before quenching, forming compact passive galaxies. Additionally, dusty starbursts in compact regions imply similar star formation mechanisms in AGN host regions as in ALMA-observed star-forming galaxies.