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Abstract: Previous molecular gas observations at arcsecond-scale resolution of theSeyfert 2 galaxy M51 suggest the presence of a dense circumnuclear rotatingdisk, which may be the reservoir for fueling the active nucleus and obscures itfrom direct view in the optical. However, our recent interferometric CO3-2observations show a hint of a velocity gradient perpendicular to the rotatingdisk, which suggests a more complex structure than previously thought. To imagethe putative circumnuclear molecular gas disk at sub-arcsecond resolution tobetter understand both the spatial distribution and kinematics of the moleculargas. We carried out CO2-1 and CO1-0 line observations of the nuclear regionof M51 with the new A configuration of the IRAM Plateau de Bure Interferometer,yielding a spatial resolution lower than 15 pc. The high resolution images showno clear evidence of a disk, aligned nearly east-west and perpendicular to theradio jet axis, as suggested by previous observations, but show two separatefeatures located on the eastern and western sides of the nucleus. The westernfeature shows an elongated structure along the jet and a good velocitycorrespondence with optical emission lines associated with the jet, suggestingthat this feature is a jet-entrained gas. The eastern feature is elongatednearly east-west ending around the nucleus. A velocity gradient appears in thesame direction with increasingly blueshifted velocities near the nucleus. Thisvelocity gradient is in the opposite sense of that previously inferred for theputative circumnuclear disk. Possible explanations for the observed moleculargas distribution and kinematics are that a rotating gas disk disturbed by thejet, gas streaming toward the nucleus, or a ring with another smaller counter-or Keplarian-rotating gas disk inside.

Autor: Satoki Matsushita, Sebastien Muller, Jeremy Lim ASIAA


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