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P. Miocchi 1,2, R. Capuzzo-Dolcetta 2, P. Di Matteo 2,3 1 INAF - Osserv. Astron. di Teramo (Teramo, Italy) 2 Dept. of Physics, Univ. of Rome “La Sapienza”

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Presentation on theme: "P. Miocchi 1,2, R. Capuzzo-Dolcetta 2, P. Di Matteo 2,3 1 INAF - Osserv. Astron. di Teramo (Teramo, Italy) 2 Dept. of Physics, Univ. of Rome “La Sapienza”"— Presentation transcript:

1 P. Miocchi 1,2, R. Capuzzo-Dolcetta 2, P. Di Matteo 2,3 1 INAF - Osserv. Astron. di Teramo (Teramo, Italy) 2 Dept. of Physics, Univ. of Rome “La Sapienza” (Rome, Italy) 3 LERMA - Observ. de Paris (Paris, France) Work supported by the INAF-CINECA agreement (http://inaf.cineca.it, key- project grants inarm033, inakp002) and by MIUR (PRIN2001).http://inaf.cineca.it Globular Clusters close interactions in galactic central regions

2 Main motivations: the study of a possible Accretion Mechanism for galactic nuclei - the study of a possible Accretion Mechanism for galactic nuclei the problem of the Super Star Clusters formation - the problem of the Super Star Clusters formation the study of the GCs mass loss and the tidal-tails  orbit path connection - the study of the GCs mass loss and the tidal-tails  orbit path connection See Di Matteo’s poster Globular Clusters interaction in galactic central regions (Concepción, 2006)

3 Murali & Weinberg, 1997, MNRAS, 288, 767. Tremaine et al, 1975, ApJ, 196, 407. Accretion of the galactic nucleus Globular Clusters interaction in galactic central regions (Concepción, 2006)  Sufficiently massive (>10 6 M  ) GCs could have spiralled into the galactic nucleus in less than 1 Gyr GCs could have accreted nuclear regions because of:  Tidal destruction  Dynamical friction  in triaxial galaxies the dynamical friction braking time t df ~ one-order of magnitude shorter than in axisymmetric or spherical potential  t df  1  M; Capuzzo-Dolcetta 1993, ApJ, 415, 616

4 Accretion of the galactic nucleus 1.To what extent can GCs survive the strong tidal bulge interaction? 2.Do they eventually merge?  What features will the merged system have? Still few numerical studies on the merging process, e.g.: Fellhauer & Kroupa, 2002, MNRAS, 330, 642 Bekki et al., 2004, ApJ, 610, L13 Globular Clusters interaction in galactic central regions (Concepción, 2006) Miocchi et al., Accepted on ApJ (astro-ph/ )

5 Tidal interactions in the central regions  Sufficiently compact clusters (c  1.2) survive the tidal interaction with the galactic potential at least for t  30 Myr. (~ 40 galactic core crossing time)  The passage through the galactic core gives rise to a tidal-shock stronger than that due to high velocity GC-GC collisions.  Tidal interactions produce further orbital decaying Globular Clusters interaction in galactic central regions (Concepción, 2006)

6 Formation of Super Star Clusters (SSC) Compact stellar systems with mass intermediate between GCs and dwarf galaxies have been observed (HST, VLT):  Nuclear Star Clusters in the centre of late-type spirals (Matthews et al. 1999, AJ, 118, 208; Böker et al. 2004, AJ, 127, 105)  Ultracompact Dwarf Galaxies (Drinkwater et al., 2000, Pub.Astron. Soc. Austr., 17, 227; Phillips et al., 2001, ApJ, 560, 201; Bekki et al., 2003, MNRAS, 344, 399) M ~ 10 6 – 10 8 M , R < 100 pc  Formation mechanisms still unclear Globular Clusters interaction in galactic central regions (Concepción, 2006)

7 The numerical model  N-body (ATD) accurate simulations (individual time-steps) with 10 6 ‘particles’ for more than 100,000 time-steps.  Galactic triaxial model (Schwarzschild-like with axial ratio 2:1.25:1 and a core mass ~ 7  10 9 M  ).  Dynamical friction included. Miocchi & Capuzzo Dolcetta, 2002, A&A, 382, clusters with: King initial profile (c ~ 0.8 – 1.2) M ~ 4.5  10 7 M  core radius ~ 10 – 20 pc ; limiting radius ~ 130 – 150 pc central vel. dispersion ~ 30 – 40 km/s Globular Clusters interaction in galactic central regions (Concepción, 2006)

8 Super Star Cluster formation Time flows top-bottom and left-right from t = 0 to t = 15 Myr. One snapshot every 1 Myr Merging among 4 clusters. length unit = 200 pc 4 clusters initially at rest with: King initial profile (c ~ 0.8 – 1.2) M ~ 4.5  10 7 M  r c ~ 10 – 20 pc ; r t ~ 130 – 150 pc  0 ~ 30 – 40 km/s 400 pc t = 0 t = 15 Myr Galactic triaxial model (axial ratio 2:1.25:1, core mass ~ 7  10 9 M  ) with dynamical friction included.

9 Super Star Cluster formation continuation from t = 16 to t = 31 Myr Dynamical equilibrium attained! 16 Myr 31 Myr Merging among 4 clusters.

10 Merging duration Centre-of-density decaying for the 4 clusters Lagrangian radii (10, 30, 50, 90%) of the whole system Merging completed 400 pc time unit = 0.8 Myr ; length unit = 200 pc Globular Clusters interaction in galactic central regions (Concepción, 2006)

11 Merging duration Centre-of-density decaying for the 4 clusters Merging completed The same without dynamical friction (simulation with N = 10 4 ) ~ 8 pc Globular Clusters interaction in galactic central regions (Concepción, 2006)

12 Super Star Cluster formation The animations simulate 15 Myr. x y y z Last configuration (t = 31 Myr) 400 pc Merging among 4 clusters. x y y z Globular Clusters interaction in galactic central regions (Concepción, 2006)

13 Super Star Cluster density profile  The final configuration of the SSC is axisymmetric (1.4:1.4:1, e = 0.3)  The formed SSC has a density profile comparable to the “sum” of the profiles of the 4 progenitor clusters  t rel >> Hubble time rhrh Globular Clusters interaction in galactic central regions (Concepción, 2006) SSC superimposed GCs 3000 M  / pc 3

14 Super Star Cluster morphology The form of the SSC inner region (< r h ) is ~ axisymmetric around z-axis Surface isodensity contours at t = 41 Globular Clusters interaction in galactic central regions (Concepción, 2006)

15 central vel. dispersion (km/sec) Super Star Cluster scaling relation The formed SSC has M = 1.9  10 8 M   0 = 150 km/s r h = 40 pc Globular Clusters interaction in galactic central regions (Concepción, 2006) From Kissler-Patig, Jordán, Bastian, 2005, astro-ph/

16 Super Star Cluster scaling relation The formed SSC has M = 1.9  10 8 M   0 = 150 km/s r h = 40 pc Globular Clusters interaction in galactic central regions (Concepción, 2006) From Kissler-Patig, Jordán, Bastian, 2005, astro-ph/

17 Conclusions  The 4 clusters merge in  18 galactic core crossing times (  14 Myr) starting from  100 pc from the galactic centre.  The resulting system attains a configuration of dynamical equilibrium.  The final spatial density is comparable with the sum of the initial cluster density profiles.  The SSC is located much closer to the GCs M-  sequence than to the elliptical galactic scaling relation.  The merging takes place also without dynamical friction, though with a  doubled time-scale Globular Clusters interaction in galactic central regions (Concepción, 2006)

18 Future Prospects  A statistically significant set of orbits and clusters has to be considered.  Inclusion of further galactic components.  Self-consistent particle representation of the bulge desirable! Globular Clusters interaction in galactic central regions (Concepción, 2006)


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