Speaker
Description
While the existence of dark matter is supported by multiple independent cosmological and astrophysical probes, its detailed physical properties remain uncertain. The Search for Milli-LEnses (SMILE) project is an international collaboration that aims to constrain the abundance of dark matter halos in the 10⁶-10⁹ Msun mass range, a hitherto poorly explored regime. The SMILE project approaches this problem through direct VLBI imaging of milliarcsecond-scale lensed images (milli-lenses) of background radio sources. As part of this effort, we conducted KVN observations at 22 and 43 GHz of promising milli-lens candidates selected from the full SMILE sample, with the goal of characterizing their millimeter-wave spectral properties and testing their lensing nature. Through rigorous visibility-domain detection tests, we obtained four secure and five tentative detections among the 17 observed sources. For several of these sources, these observations represent their first reported detections at 22 GHz. These detections enabled us to apply several key diagnostics for gravitational lensing, including surface-brightness conservation, invariance of spectral shape, and flux-ratio stability across epochs. In this talk, we present the details of these results and discuss their implications for current models of dark matter.