Improved Polar PM + SPH + SF code. â More accurate self-forces (sub-gridding). â Spatial resolution increased (15 pc in the central region). â CFL condition ...
Nuclear velocity drops in barred galaxies (σ-drops) Hervé Wozniak & Nicolas Champavert Centre de Recherche Astronomique de Lyon, France 2005 march 10th
Why studying the stellar kinematics of sub-kpc regions in barred galaxies?
Region well inside the bar but outside immediate vicinity of any AGN More or less the region where secondary/nuclear bars are expected to develop Should shed some light on nuclear fuelling mechanisms
2005/03/10
2
What should be a ‘normal’ stellar kinematics ? unexpected NGC 4143 (SAB)
An incomplete census… not statistics Emsellem et al. 2001
NGC 1097
SB(s)b
NGC 1068
SAb (SB!)
NGC 1138
SBO
NGC 1808
SAB(s:)b
Sy 2
Emsellem et al. 2001
NGC 2639
SA(r)a
Sy 1.9
Marquez et al. 2003
NGC 3412
SB0(s)
NGC 3593
SA(s)0/a
Sy 2
Bertola et al. 1993
NGC 3623
SAB(rs)a
Liner
De Zeeuw et al. 2002
NGC 3627
SBb
Liner/Sy 2
Héraudeau & Simien 1998
NGC 4303
SBbc
Sy 2
Héraudeau & Simien 1998
NGC 4579
SBb
Liner/Sy 1.9
Héraudeau & Simien 1998
NGC 4725
SBab
Sy 2
Héraudeau et al. 1999
NGC 4477
SB0
Sy 2
Jarvis et al. 1988
NGC 5728
SABb(r)
Sy 2
Emsellem et al. 2001
NGC 6503
SA(s)cd
Liner/HII
Bottema 1993; Bottema & Gerritsen 1997
NGC 6814
SAB(rs)bc
Sy 1.5
Marquez et al. 2003
NGC 6951
SAB(rs)bc
Sy 2
Marquez et al. 2003
SB(r)a
Sy 2
Marquez et al. 2003
IC 184 2005/03/10
Sy
Emsellem et al. 2005 Simien & Prugniel 2002
Aguerri et al. 2003
7
Tentative dynamical models…
Bottema & Gerritsen (1997):
N-body simulations (only collisionless particles) Analytical models with/without halo Ad hoc additional ‘cold’ nuclear sphere
Emsellem et al. (2001):
Damped orbits around resonances (Lindblad & Lindblad 1994 formalism) Bulge (Plummer) + Disk (KuzminToomre) + nuclear disk Parameters fitted on V and σ curves
2005/03/10
8
… and successful simulations Wozniak et al. (2003 A&A 409, 469)
Cartesian PM + sticky particles + SF Schmidt law
T= 0: 305 000 *, 76 000 gas
Two stellar populations:
T= 0: 500 000 *, 50 000 gas
‘initial’ population ‘new’ population born during the run
Many runs:
isothermal gas (various initial temperatures and σ) or cooling With/without rigid halo Various resolution and smoothing lengths
2005/03/10
9
Mechanisms of drop formation
Reservoir of gas in the sub-kpc region
By accretion
Active star formation
need a bar (not necessarily a nuclear/secondary bar) or any other non-axisymmetric feature (e.g. nuclear spirals?) From satellites ? Possible but not tested
New stars inherit the gas velocity dispersion at birth Since gas has a lower σ than stars ⇒ σ-drop
Issue: lifetime of a σ-drop
No more gas Stopped or low-rate star formation
2005/03/10
10
σ-drop lifetime ? Wozniak & Champavert 2005
Improved Polar PM + SPH + SF code
More accurate self-forces (sub-gridding) Spatial resolution increased (15 pc in the central region) CFL condition ⇒ very small time steps ⇒ CPU consuming T= 0: 2 500 000 *, 50 000 gas SF switched off at various time
Depth of a σ–drop: 〈σR〉 (r < 100 pc) = σmin 〈σR〉 (r = 500 ± 50 pc) = σ’max’ Δ σ = σ’max’ - σ min 2005/03/10
11
σ-drop evolution
• 0 < T < 475 Myr: bar formation phase, gas accretion, growing local SFR •475 < T < 800: growing phase; new population more massive than initial one in central region
•T > 800: nearly stable phase but slow heating at the same rate in both regions σ reaches a plateau (→ 2.1 Gyr!)
2005/03/10
12
σ-drop evolution ___ = run with SF ___ = pure N-body run
2005/03/10
13
σ-drop evolution ___ = run with SF ___ = pure N-body run ___ = SF stopped at t=1000 Myr
2005/03/10
14
σ-drop evolution ___ = run with SF ___ = pure N-body run ___ = SF stopped at t=1000 Myr
2005/03/10
15
σ-drop evolution ___ = run with SF ___ = pure N-body run ___ = SF stopped at t=1000 Myr ___ = SF stopped at t= 800 Myr
2005/03/10
16
σ-drop evolution ___ = run with SF ___ = pure N-body run ___ = SF stopped at t=1000 Myr ___ = SF stopped at t= 800 Myr ___ = SF stopped at t= 400 Myr Strong gas accumulation in the central region
2005/03/10
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Conclusions Nuclear drops in stellar velocity dispersion are likely to be due to a new population which is born in low-σ gas accreted in the central region
1.
σ-drops could be long-lived, despite secular heating, provided:
2.
2005/03/10
reservoir of gas is regularly refilled star formation is ongoing (even a low rate 〈 1 M~ yr -1 in the central 100 pc)
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