Doi, Akihiro

ALMA continuum spectrum of the M87 nucleus.

Author list: Akihiro Doi, Kazuhiro Hada, Hiroshi Nagai, Motoki Kino, Mareki Honma, Kazunori Akiyama, Tomoaki Oyama, Yusuke Kono

We report the result of ALMA continuum observations toward the M87 nucleus at thirty-six frequencies (quasi-simultaneously) ranging from 90 GHz to 700 GHz.  We found a spectral break at the millimeter regime: a nearly flat spectrum at lower frequencies and a steep spectrum at higher frequencies. The spectral profile may suggest (1) a possible high-frequency end of previously observed core shift of jets and (2) an optically thin line-of-sight to the expected radius of a black hole shadow for a future submm VLBI imaging.