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.

Motivation

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

12CO(2-1)SMA

12CO(3-2)SMA

Sakamoto et al.(1999, ApJS, 124, 403)

810 pc

12CO(1-0) NMA

Matsushita et al. (2004, ApJL, in

press)

Sawada-Satoh et al.

Optical image of M51

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.

Sample selection

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 Mּס. 55”

Results(1)12CO 12CO

13CO13CO

C18O C18O

100 pc

100 pc

100 pc

100 pc

100 pc

100 pc

Intensity maps Velocity maps

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 Mּס

Pα emission shows a ring like structure with 10” in diameterMarconi et al. 2000

10”, 200 pc

continuum emission

RA continuum map

DE

C

SED of NGC 4945 Log [Hz]

• SED rules out synchrotron emission.• Size continuum ~ 300 pc, same as C18O.• Continuum likely from dust.

Flux density Log [J

y]

Synchrotron Radiation

SMA

continuum emission

RA continuum map

DE

C

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 Mּס

- Molecular gas Mass derived from dust = 7 x 108 Mּס(gas/dust=100)

- Enclosed mass within 380 pc = 3 x 109 Mּס

- 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

• Bright IRAS source (at 100 μm) with 75% emission concentrated at central 12” x 9” region.

• Moderate star formation rate: ~0.4Mּס/yr (from infrared luminosity)

• Starburst ring in Pα, inner 100 pc and 200 pc outside.

• Conical structure in optical.

True color RGB image shows a conical structure originated from the central 100 pc region

Moorwood et al. 1996, Marconi et al. 2000

Pα emission shows a ring like structure with 10” in diameter

100 pc

100 pc