16794

We propose to obtain high-resolution radio continuum emission observations with the VLBA at 1.4GHz (21-cm L band) to confirm a candidate dual QSO at z=1.87 comma a redshift that is nearer to d_commacosmic noond_comma than the current dual-AGN record holder by virgul2 Gyr of lookback time. We identified the source based on HST WFC3-IR images showing two closely-separated point sources (at a projected separation of 0.26 arcsec comma or virgul2 kpc). The source in question is a dust-reddened quasar comma which is a population typically hosted by major mergers. We also propose to obtain a spatially-resolved STIS spectrum of the system with HST comma in the visible spectral range comma in order to measure the CIIICORCHETE_CLOSE and MgII line properties of each component. These measurements will confirm the source as a bone-fide dual QSO comma which would make it the highest redshift dual AGN reported to date -- at the era of peak AGN and merger activity. The measurements will also provide black hole masses comma accretion rates comma and radio loudnesses of each component comma for comparison with models. These results will link dust-reddening and galaxy mergers to black hole mergers opening up a new population in which to search for samples of dual AGN.