Searching for circumnuclear molecular torus in Seyfert galaxy NGC 4945 Outline: Motivations Observations--SMA Results Summary

Motivation Search for circumnuclear molecular torus in Seyfert galaxies. Measure physical properties. Replenishment of the torus. Probe gravitational potential.

Matsushita et al. (2004, ApJL, in press) Motivation Search for circumnuclear molecular torus in Seyfert galaxies. Measure physical properties. Replenishment of the torus. Probe gravitational potential. Optical image of M51 12CO(1-0) NMA 12CO(2-1) SMA 12CO(3-2) SMA 810 pc Sawada-Satoh et al. Matsushita et al. (2004, ApJL, in press) Sakamoto et al. (1999, ApJS, 124, 403)

Sample selection NGC 4945: Seyfert 2 Distance ~ 3.9 Mpc (1” = 19 pc), one of closest Seyfert galaxies. DEC = - 490, only accessible mm/sub-m interferometer is SMA.

Observation--SMA Observe on: 5.24.2004 Compact configuration N-S elongation (7 x 6m ants) FWHM primary beam: 55” = 1.1 kpc Synthesized beam: 5.1” x 2.8” (100 x 60 pc) Wide bandwidth of SMA (4 GHz), observe 12CO, 13CO, C18O and continuum together. Detection limit ~ 106 Mסּ. 55”

Intensity maps Velocity maps Results(1) Intensity maps Velocity maps 12CO 12CO 100 pc 100 pc 13CO 13CO 100 pc 100 pc C18O C18O 100 pc 100 pc

Results(2)—P-V diagram Solid body rotation with gradient = 1160 kms-1 kpc-1, ( tracing rising part of rotation curve). Molecular gas ring coinciding with starburst ring. Dynamical mass within 380 pc = 3 x 109 Mסּ 10”, 200 pc Pα emission shows a ring like structure with 10” in diameter Marconi et al. 2000

continuum emission Flux density Log [Jy] DEC SMA RA continuum map Synchrotron Radiation SMA RA continuum map SED of NGC 4945 Log [Hz] SED rules out synchrotron emission. Size continuum ~ 300 pc, same as C18O. Continuum likely from dust.

continuum emission DEC RA continuum map C18O intensity map SED rules out synchrotron emission. Size continuum ~ 300 pc, similar as C18O. Continuum likely from dust.

Discussion Central gas concentration - Rotating disk within 380 pc  molecular torus? central disk? - Molecular gas mass from 12CO, 13CO and C18O = 108 – 109 Mסּ - Molecular gas Mass derived from dust = 7 x 108 Mסּ(gas/dust=100) - Enclosed mass within 380 pc = 3 x 109 Mסּ - MBH < 106 (From H2O megamaser Greenhill et al. 1996)  enclosed mass dominated by stars. - Non-circular motion from 380 – 900 pc  need to model kinematics The molecular gas could be ring, or torus. We need higher resolution observation.

Summary & Future work Two possiblilities - Circumnuclear molecular torus size 380 pc with mass dominated by stars. - Molecular gas (disk) settled into central gravitational potential. Image at higher angualr resolution. Higher CO transitions.

Starburst activity Pα emission shows a ring like structure with 10” in diameter 100 pc Bright IRAS source (at 100 μm) with 75% emission concentrated at central 12” x 9” region. Moderate star formation rate: ~0.4Mסּ/yr (from infrared luminosity) Starburst ring in Pα, inner 100 pc and 200 pc outside. Conical structure in optical. 100 pc True color RGB image shows a conical structure originated from the central 100 pc region Moorwood et al. 1996, Marconi et al. 2000