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
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