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 ( key- project grants inarm033, inakp002) and by MIUR (PRIN2001). Globular Clusters close interactions in galactic central regions

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)

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

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/ )

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)

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)

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)

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.

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

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)

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)

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)

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

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)

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/

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/

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)

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)