Molecular Distribution in the Central Region of M87

Abstract

The central region of M87 has been observed by the Atacama Large Millimeter/submillimeter Array (ALMA) several times to resolve its molecular cloud distribution. We present the ALMA CO(1–0), CO(2–1), and CO(3–2) observations of the M87 circumnuclear region. The CO(1–0) shows emission as well as molecular absorption features toward its nucleus, indicating the existence of cold molecular clouds/gas. ALMA imaging of the CO(1–0) observations show the distribution of molecular clouds toward the nucleus of M87 with a radius of ∼105 pc. The clouds seen in the CO(1–0) are moving with very high velocity and have an apparent motion in the range of −1000 to 3600 km s ^−1 relative to the central supermassive black hole, which has a systemic velocity of ∼1266 km s ^−1 . The molecular gas mass was estimated to be about 1.08 ± 0.64 × 10 ^7 M _⊙ in the central 210 pc of M87. We calculated the optical depths using the absorption lines of the CO(1–0) and CO(2–1). The excitation temperature was estimated to be ∼7.133 ± 0.03 K using the optical depth ratio of the CO(2-1) to CO(1-0). We also found the line-of-sight column density to be ∼2.25 × 10 ^15 cm ^−2 , which corresponds to a hydrogen column density of ∼0.28 × 10 ^20 cm ^−2 .

Keywords

• Supermassive black holes
• Active galactic nuclei
• Galaxy circumnuclear disk