Issue |
A&A
Volume 433, Number 1, April I 2005
|
|
---|---|---|
Page(s) | 43 - 56 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20035737 | |
Published online | 14 March 2005 |
A wide-field photometric study of the globular cluster system of NGC 4636*
1
Universidad de Concepción, Departamento de Física, Casilla 160-C, Concepción, Chile e-mail: bdirsch@cepheid.cfm.udec.cl
2
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53123 Bonn, Germany
Received:
24
November
2003
Accepted:
3
November
2004
Previous smaller-scale studies of the globular cluster system of NGC 4636, an
elliptical galaxy in the southern part of the Virgo cluster, have revealed an
unusually rich globular cluster system. We re-investigate the cluster system of
NGC 4636 with wide-field Washington photometry. The globular cluster luminosity
function can be followed roughly 1 mag beyond the turn-over magnitude found at
for the blue cluster sub-population. This corresponds to
a distance modulus of
, 0.4 mag larger than the
distance determined from surface brightness fluctuations. The high specific frequency
is confirmed, yet the exact value remains uncertain because of the uncertain
distance: it varies between
and
. The globular cluster system
has a clearly bimodal color distribution. The color peak positions show no radial
dependence and are in good agreement with the values found for other galaxies studied
in the same filter system. However, a luminosity dependence is found: brighter
clusters with an “intermediate” color exist. The clusters exhibit a shallow radial
distribution within 7´, represented by a power-law with an exponent of -1.4.
Within the same radial interval, the galaxy light has a distinctly steeper profile.
Because of the difference in the cluster and light distribution the specific
frequency increases considerably with radius. At 7´ and 9´ the
density profiles of the red and blue clusters, respectively, change strongly: the
power-law indices decrease to around -5 and become similar to the galaxy profile.
This steep profile indicates that we reach the outer rim of the cluster system at
approximately 11´. This interpretation is supported by the fact that in
particular the density distribution of the blue cluster population can be well fit by
the projection of a truncated power-law model with a core. This feature is seen for
the first time in a globular cluster system. While the radial distribution of the
cluster and field populations are rather different, this is not true for the
ellipticity of the system: the elongation as well as the position angle of the
cluster system agree well with the galaxy light. We compare the radial distribution
of globular clusters with the light profiles for a sample of elliptical galaxies.
The difference observed in NGC 4636 is typical of an elliptical galaxy of this luminosity.
The intrinsic specific frequency of
the blue population is considerably larger than that of the red one.
Key words: galaxies: elliptical and lenticular, cD / galaxies: individual: NGC 4636 / galaxies: star clusters / galaxies: stellar content / galaxies: structure
© ESO, 2005
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.