Oral Presentation

Millimeter VLBI observations with ALMA: Overview of the first results

Author(s): Kazunori Akiyama

Presenter: Kazunori Akiyama (NRAO / MIT Haystack Observatory)

The immediate vicinity of a black hole is a critical region to understand high-energy astrophysical phenomena such as accretion and jet formation. This region may also provide images imprinting general relativistic effects, such as a shadow of the black hole illuminated by a photon ring. Although such regions have been accessible with the recent advent of short-millimeter global VLBI array such as the Global Millimeter VLBI Array (GMVA) at 3 mm and the Event Horizon Telescope (EHT) at 1.3 mm, observational capabilities of these arrays have been limited by severe atmospheric conditions affecting their sensitivities. Here, we present an overview of the first millimeter VLBI observations including ALMA toward the Galactic center Sgr A* and two nearby active galactic nuclei. The crucial addition of the very high sensitive ALMA enhances the sensitivity of overall arrays by an order of magnitude as well as provides the highest angular resolutions ever at the observing frequencies. This allows to resolve and image the structure of ~10 Schwartzchild radii for Sgr A* and dynamically collimating jets inside the sphere of the gravitational influence for nearby AGNs, providing new insights for all of the first target sources. Finally, we introduce on-going efforts and near-time forecast of black hole imaging with the EHT observations with ALMA.