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RevMexAA (Serie de Conferencias), 44, 115–115 (2014)

GLOBULAR CLUSTERS AS TRACERS OF THE HIERARCHICAL

FORMATION OF THE MILKY WAY

J. A. Carballo-Bello1,2,3, D. Mart́ınez-Delgado4, A. Sollima5, and R. R. Muñoz1

Globular clusters have played an important

role in the study of the processes that led to

the formation of our Galaxy. Moreover, the

dual Galactic globular cluster system is con-

sidered a manifestation of its hierarchical for-

mation in the context of the Λ-CDM scenario.

Wide-field imaging - as the one obtained in

our work - and follow-up spectroscopy are

crucial tools to unveil the remnants of their

progenitor dwarf galaxies, in some cases un-

known stellar systems already assimilated by

the Milky Way.

Globular cluster (GC) systems contain valuableinformation about the formation process of the hostgalaxy. The existence of two subcomponents in theGalactic GC population was interpreted as evidencewhich supports the hierarchical galaxy formation inthe Λ-CDM scenario (Searle & Zinn 1978; Tonini2013). The outer halo clusters (RG ≥ 15 kpc) wereprobably formed in small fragments subsequently ac-creted by the Galaxy, whereas the inner clusters wereformed in situ. In this context, we expect part of theGalactic GC system to be associated with some ofthe tidal streams that populate the outer halo, simi-lar to what has been observed in the M31 outer GCsystem, which coincides with the stellar substruc-tures around that galaxy (Mackey et al. 2010). Ifthese GCs were formed in already accreted systems,these clusters might be still surrounded by the tidalremnants generated by the disruption of their pro-genitor galaxies.

We have obtained deep wide-field photometry for23 GCs lying in the distance range 10 ≤ RG ≤40 kpc, which might include the suggested transitionregion between accreted and in-situ formed Galac-tic stellar halo (Carollo et al. 2007). The observa-tions were made with the WFC at the Isaac Newton

1Departamento de Astronomı́a, Universidad de Chile,Camino El Observatorio 1515, Las Condes, Santiago, Chile.

2Instituto de Astrof́ısica de Canarias (IAC), Vı́a Lácteas/n, La Laguna E-38205, S/C de Tenerife, Spain.

3Departamento de Astrof́ısica, Universidad de La Laguna,La Laguna E-38205, S/C de Tenerife, Spain.

4Max Planck Institut für Astronomie, D69117 Heidelberg,Germany.

5INAF - Observatorio Astronomico di Padova, I35122Padova, Italy.

Fig. 1. Examples of CMDs obtained for Whiting 1 andNGC 1851 (left) and the area surrounding them (right).

Telescope (La Palma, Spain) and the WFI at theESO2.2 m telescope (La Silla, Chile). For each clus-ter we obtained a color-magnitude diagram (CMD)for the cluster content and a second diagram corre-sponding to those stars beyond 1.5 rt. In the lattercase, we have detected the presence around a halfof the sample of underlying tidal remnants possi-bly associated with their progenitor galaxies. Glob-ulars such as Whiting 1 and NGC 7492 seem to beinmersed in the tidal stream generated by the disrup-tion of the Sagittarius dwarf spheroidal and a newunderlying system has been unveiled in the back-ground of NGC 1851, with the help of follow-up spec-troscopy (Sollima et al. 2012). Further observationsof the area around these clusters and an analysis ofthe kinematics of the subjacent populations will shedlight on the nature of these systems.

REFERENCES

Searle, L. & Zinn, R. 1978, ApJ, 225, 357Tonini, C. 2013, ApJ, 762, 39Mackey, A. D. et al. 2010, ApJL, 717, L11Carollo, D. et al., 2007, Nat, 450, 1020Sollima, A. et al. 2012, MNRAS, 426, 1137

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