Globular Clusters close interactions in galactic central regions

1. Globular Clusters close interactions in galactic central regions P. Miocchi1,2, R. Capuzzo-Dolcetta2, P. Di Matteo2,3 1INAF - Osserv. Astron. di Teramo (Teramo, Italy) 2Dept. of Physics, Univ. of Rome “La Sapienza” (Rome, Italy) 3LERMA- Observ. de Paris (Paris, France) Work supported by the INAF-CINECA agreement (http://inaf.cineca.it, key-project grantsinarm033, inakp002) and by MIUR (PRIN2001).

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

3. Globular Clusters interaction in galactic central regions (Concepción, 2006) Accretion of the galactic nucleus GCs could have accreted nuclear regions because of: • Tidal destruction • Dynamical friction Murali & Weinberg, 1997, MNRAS, 288, 767. Tremaine et al, 1975, ApJ, 196, 407. • in triaxial galaxies the dynamical friction braking timetdf ~ one-order of magnitude shorter than in axisymmetric or spherical potential • tdf 1  M; Capuzzo-Dolcetta 1993,ApJ, 415, 616 ß Sufficiently massive (>106 M) GCs could have spiralled into the galactic nucleus in less than 1 Gyr

4. Globular Clusters interaction in galactic central regions (Concepción, 2006) Accretion of the galactic nucleus • To what extent can GCs survive the strong tidal bulge interaction? • Do they eventually merge? • What features will the mergedsystem have? Miocchi et al., 2005. Accepted on ApJ (astro-ph/0501618) Still few numerical studies on the merging process, e.g.: • Fellhauer & Kroupa, 2002, MNRAS, 330, 642 • Bekki et al., 2004, ApJ, 610, L13

5. Globular Clusters interaction in galactic central regions (Concepción, 2006) 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 strongerthan that due to high velocity GC-GC collisions. • Tidal interactions produce further orbital decaying

6. 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~ 106 –108 M , R < 100 pc  Formation mechanisms still unclear

7. t = 0 400 pc t = 15 Myr length unit = 200 pc Super Star Cluster formation Merging among 4 clusters. Galactictriaxialmodel (axial ratio 2:1.25:1, core mass ~ 7  109 M ) with dynamical frictionincluded. 4 clusters initially at rest with: King initial profile (c ~ 0.8 – 1.2) M ~ 4.5  107 M rc ~ 10 – 20 pc ; rt ~ 130 – 150 pc 0 ~ 30 – 40 km/s Time flows top-bottom and left-right from t = 0 to t = 15 Myr. One snapshot every 1 Myr

8. 16 Myr 31 Myr Super Star Cluster formation Merging among 4 clusters. Dynamical equilibrium attained! continuation from t = 16 to t = 31 Myr

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

10. Globular Clusters interaction in galactic central regions (Concepción, 2006) Merging duration Merging completed ~ 8 pc Centre-of-density decaying for the 4 clusters The same without dynamical friction (simulation with N = 104)

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

12. Globular Clusters interaction in galactic central regions (Concepción, 2006) 3000 M / pc 3 SSC superimposed GCs 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 • trel >> Hubble time rh

13. 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  108 M 0= 150 km/s rh = 40 pc From Kissler-Patig, Jordán, Bastian, 2005, astro-ph/0512360

14. Globular Clusters interaction in galactic central regions (Concepción, 2006) Super Star Cluster scaling relation The formed SSC has M = 1.9  108 M 0= 150 km/s rh = 40 pc From Kissler-Patig, Jordán, Bastian, 2005, astro-ph/0512360

15. Globular Clusters interaction in galactic central regions (Concepción, 2006) 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 dynamicalequilibrium. • 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 mergingtakes place also without dynamical friction, though with a doubled time-scale

16. 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!