Detalles de publicación
PP 019097
A dwarf-dwarf merger and dark matter core as a solution to the Globular Cluster problems in the Fornax dSph
MPIA, Heidelberg, Germany; Department of Astrophysics; University Vienna, Wien, Austria; Instituto de Astrofisica de Canarias, Tenerife, Spain; Departamento de Astrofisica, Universidad de La Laguna, enerife, Spain
The five globular clusters (GCs) of the Fornax dSph are puzzling for two
reasons; the mass in GCs is high with respect to the galaxy's old stellar mass,
and their survival and large distance (> 1 kpc) is at odds with naive
expectations of dynamical friction. We present here a semi-analytic model,
simultaneously addressing both problems in a comprehensive evolutionary
framework for Fornax. Key to the model is inclusion of: 1) hydrodynamical
constraints on the GC formation locations, 2) self-consistent velocity
distribution functions in the dynamical friction calculations and 3) expansion
of GC orbits due to a past dwarf-dwarf merger in the orbit integrations. The
latter is crucial for reconciling the dynamical survival of the clusters, and
their chemical properties with respect to the Fornax field stars. We find that
in order for four of the GCs to survive at their observed projected location, a
dark matter core of radius > 1.5 kpc and a dwarf merger with dynamical mass
ratio of 1:5 to 1:2 with Fornax is required. We support the merger scenario by
showing that aspects of the field star metallicity distribution function and
anomalous chemical properties of GC5, are representative of a merging galaxy
which is ~1/3 less massive than Fornax. Together the chemical and dynamical
models suggest a scenario where three in-situ GCs in proto-Fornax were ejected
to the outskirts during the merger, a GC4 formed during the merger at about 10
Gyrs ago, with GC5 being brought in by the merging galaxy to Fornax.
reasons; the mass in GCs is high with respect to the galaxy's old stellar mass,
and their survival and large distance (> 1 kpc) is at odds with naive
expectations of dynamical friction. We present here a semi-analytic model,
simultaneously addressing both problems in a comprehensive evolutionary
framework for Fornax. Key to the model is inclusion of: 1) hydrodynamical
constraints on the GC formation locations, 2) self-consistent velocity
distribution functions in the dynamical friction calculations and 3) expansion
of GC orbits due to a past dwarf-dwarf merger in the orbit integrations. The
latter is crucial for reconciling the dynamical survival of the clusters, and
their chemical properties with respect to the Fornax field stars. We find that
in order for four of the GCs to survive at their observed projected location, a
dark matter core of radius > 1.5 kpc and a dwarf merger with dynamical mass
ratio of 1:5 to 1:2 with Fornax is required. We support the merger scenario by
showing that aspects of the field star metallicity distribution function and
anomalous chemical properties of GC5, are representative of a merging galaxy
which is ~1/3 less massive than Fornax. Together the chemical and dynamical
models suggest a scenario where three in-situ GCs in proto-Fornax were ejected
to the outskirts during the merger, a GC4 formed during the merger at about 10
Gyrs ago, with GC5 being brought in by the merging galaxy to Fornax.