IALP   13078
INSTITUTO DE ASTROFISICA LA PLATA
Unidad Ejecutora - UE
artículos
Título:
A quantitative link between globular clusters and the stellar haloes in elliptical galaxies
Autor/es:
FORTE J. C.; FAIFER F. R.; GEISLER D.
Revista:
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
Editorial:
Blackwell Synergy
Referencias:
Lugar: Londres, Inglaterra; Año: 2007 vol. 382 p. 1947 - 1964
ISSN:
0035-8711
Resumen:
This paper explores the quantitative connection between globular
clusters and the `diffuse' stellar population of the galaxies they are
associated with. Both NGC 1399 and NGC 4486 (M87) are well suited for
this kind of analysis due to their large globular cluster populations.
The main assumption of our Monte Carlo based models is that each
globular cluster is formed along with a given diffuse stellar mass that
shares the same spatial distribution, chemical composition and age. The
main globular cluster subpopulations, that determine the observed
bimodal colour distribution, are decomposed avoiding a priori parametric
(e.g. Gaussian) fits and using a new colour (C -
T1)-metallicity relation. The eventual detectability of a
`blue' tilt in the colour-magnitude diagrams of the blue globular
cluster subpopulation is also addressed.
A successful link between globular clusters and the stellar galaxy halo
is established by assuming that the number of globular clusters per
associated diffuse stellar mass t is a function of total abundance [Z/H]
and behaves as t = γ exp(-δ[Z/H]) (i.e. increases when
abundance decreases).
The simulations allow the prediction of a surface brightness profile for
each galaxy through these two free parameters' approximation. The
γ, δ parameters that provide the best fit to the observed
profiles in the B band, in turn, determine several features, namely,
large-scale halo colour gradients, globular cluster-halo colour offset,
clusters' cumulative specific frequencies, and stellar metallicity
distributions, that compare well with observations.
The results suggest the co-existence of two distinct stellar populations
characterized by widely different metallicities and spatial
distributions. One of these populations (connected with the blue
globular clusters) is metal poor, highly homogeneous, exhibits an
extended spatial distribution and becomes more evident at large
galactocentric radius contributing with some 20 per cent of the total
stellar mass. In turn, the stellar population associated with the red
globular clusters is extremely heterogeneous and dominates the inner
region of both galaxies.
Remarkably, and although the cluster populations of these galaxies
exhibit detectable differences in colour distribution, the δ
parameter that determines the shape of the brightness profiles of both
galaxies has the same value, δ ~ 1.1 to 1.2 +/- 0.1.