Imaging black holes with sparse modeling

[摘要] We introduce a new imaging method for radio interferometry based on sparse- modeling. The direct observables in radio interferometry are visibilities, which are Fourier transformation of an astronomical image on the sky-plane, and incomplete sampling of visibilities in the spatial frequency domain results in an under-determined problem, which has been usually solved with 0 filling to un-sampled grids. In this paper we propose to directly solve this under-determined problem using sparse modeling without 0 filling, which realizes super resolution, i.e., resolution higher than the standard refraction limit. We show simulation results of sparse modeling for the Event Horizon Telescope (EHT) observations of super-massive black holes and demonstrate that our approach has significant merit in observations of black hole shadows expected to be realized in near future. We also present some results with the method applied to real data, and also discuss more advanced techniques for practical observations such as imaging with closure phase as well as treating the effect of interstellar scattering effect.

[发布机构] Mizusawa VLBI Observatory, National Astronomical Observatory of Japan, Hoshigaoka, Ohshu, Iwate; 023-0861, Japan^1;Department of Astronomical Science, SOKENDAI (The Graduate University for Advanced Studies), Hoshigaoka, Ohshu, Iwate; 023-0861, Japan^2;Department of Astronomy, Graduate School of Science, University of Tokyo, Hongo, Bunkyo-ku, Tokyo; 113-0033, Japan^3;Haystack Observatory, Massachusetts Institute of Technology, Route 40, Westford; MA; 01886, United States^4;Institute of Statistical Mathematics, Tachikawa, Tokyo; 190-8562, Japan^5;Department of Statistical Science, SOKENDAI (The Graduate University for Advanced Studies), Tachikawa, Tokyo; 190-8562, Japan^6;Astrophysical Science Center, Hiroshima University, Higashi-Hiroshima, Hiroshima; 739-8526, Japan^7

[关键词] Astronomical images;Fourier transformations;Incomplete samplings;Massive black holes;Radio interferometry;Scattering effects;Spatial frequency domains;Under-determined