Personal Presentation and Info

Mi name is Sofía Gallego Gallego, I'm a master student at Pontificia Universidad Católica de Chile.
This work was made for mi undergraduate thesis and first research of my master, with supervision of PhD Jorge Cuadra, professor at this University.

Inroduction

Motivation:

• Observational evidence of activity in the Galactic Center (CG) around several millions ago.
• Unusual star formation in the GC.
• On smaller scales, the existence of massive and young stars in the Central cluster.

It is expected that a large amount of gas is supplied into the center from the Central Molecular Zone (CMZ), a ring-like structure of ~180 pc radius and (5−10)×1e7 Msun

Possible Explanation: Satellite galaxy merge with the Milky way, who perturbs stable gas in the CMZ, driving the gas to inner regions in shorter timescales than natural inflow (Lang et al. 2011).
Expected 1e5 Mʘ infall in 10 Myr.

Model & Methodology

We model the satellite merger scenario through hydrodynamical Gadget-2 simulations, using a rotating bar potential from Zhao et al. 1994

where (r, θ, φ) are the spherical coordinates fixed in the bar,

and

Based on recent simulations on the inner kiloparsecs region (Kim et al. 2011) we used the following parameters: α = 1.75, b20 = 0.3, b22 = 0.1, ρ0 = 40 Msun pc^−3, r0 = 100 pc. The bar is rotating with a pattern speed of 63 km /s kpc . Given a bar axis ratio of [1 : 0.74 : 0.65], an X1 − X2 transition at r ∼ 200 pc, inner Lindblad Resonance 660 pc and a corotation radius of 2.8 kpc. Enclosed mass inside 200 pc is 1e9 Msun.

The gas in the CMZ is more especifically a cold torus centered on the 180 pc, and extended radially from 130 pc to 230 pc (Launhardt et al. 2002). From Ferrière et al. 2007, the space-averaged density of hydrogen in the torus can be approximated by

 

 with L~55pc and H~29pc.

Periodic and non self-intersecting orbits of the CMZ gas in the x-y plane were  obtained through the shooting technique, integrating the equations of motion with a fourth order Runge-Kutta method.

Our fiducial model consist in around 300.000 particles, with T=1000K. Gas particles where simulated without satellite for 20 Myr in order to get a hydrodynamically relaxed distribution of particles.  Satellite orbit considers dynamical friction.

Results & Conclusions

Results

Sample Videos:

Without Satellite

With Satellite

Mass Deposition With Satellite

Mass Deposition Without Satellite

 

• Inflow of 1e5 Mʘ around 70 Myr after satellite collision.
• Simulations without satellite show a similar inflow around 90 Myr.
• Only a small fraction of the gas (~104 Mʘ) reaches the inner 80 pc, and in smaller scales even less.

Conclusions

Simulations do show inflow of gas due to satellite perturbation but comparable to natural instabillity. At lower scales pertubation doesn't seem sufficient to produce star clusters at 30 pc, neither star formation at inner regions.