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 (0.1 arcsec - 0.4 arcsec) and HST/F814W imaging (~ 0.1 arcsec). Our
sample includes 27 galaxies at z<2.5, classified as infrared-selected AGN (3
sources), X-ray selected AGN (4 sources), and non-AGN star-forming galaxies (20
sources), for which high-resolution Band 6/7 ALMA images are available at 1 mm
from our own observing program as well as archival observations. The sizes and
SFR surface densities measured from both ALMA/1 mm and HST/F814W images show
that obscured AGN host galaxies are more compact than non-AGN star-forming
galaxies at similar redshift and stellar mass. This result suggests that the
obscured accretion phase may be related to galaxies experiencing a compaction
of their gaseous component, which could be associated with enhanced central
star formation before a subsequent quenching driving the formation of compact
passive galaxies. Moreover, most of the detected and stacked rest-frame FIR
sizes of AGNs in our sample are similar or more compact than their rest-frame
optical sizes, which is consistent with recent results of ALMA detected
sources. This might be explained by the fact that the dusty starbursts take
place in the compact regions, and suggests that the star formation mechanisms
in the compact regions of AGN hosts are similar to those observed in
star-forming galaxies observed with ALMA.
