Issue |
A&A
Volume 398, Number 1, January IV 2003
|
|
---|---|---|
Page(s) | 63 - 79 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20021597 | |
Published online | 14 January 2003 |
Surface brightness fluctuation distances for dwarf elliptical galaxies in the Fornax cluster*
Research School of Astronomy and Astrophysics, The Australian National University, Mt Stromlo Observatory, Cotter Road, Weston ACT 2611, Australia
Corresponding author: jerjen@mso.anu.edu.au
Received:
20
September
2002
Accepted:
30
October
2002
We have obtained deep B and R-band CCD images of eight dwarf elliptical (dE) galaxies
in the Fornax cluster using the FORS1 instrument at the VLT in service mode under excellent
atmospheric conditions. A total of 92 fields distributed over the central regions of the
galaxies have been analysed to measure local colours and R-band surface
brightness fluctuation (SBF) magnitudes
. Within a galaxy the observed
correlation of
with
follows closely the predicted slope of the
colour–fluctuation luminosity relation for composite single-burst, mainly old, metal-poor
stellar populations. This allows to determine the distances of the dEs from simple offset
measurements to a typically 9% accuracy. The distance distribution of these genuine cluster
dwarfs centers at a mean distance of
mag, or 20.3 ± 0.7 Mpc,
a value that is in best agreement with previous SBF work on Fornax early-type giants and thus
represents a robust estimate of the distance to the Fornax cluster core. The application of the
bootstrap resampling technique on the distance data further reveals a cluster
depth of
Mpc. We take this preliminary result as a
confirmation of the compact appearance of Fornax in the projection on the sky although
the cluster might be slightly more elongated along the line of sight.
Combining the newly derived cluster distance with the cosmological velocity
of Fornax of
km s-1 gives a Hubble constant of
km s-1 Mpc-1.
This value is consistent at the 95% confidence level with both the most recent result from
the team that favours a long distance scale and the final value adopted by the HST “Key Project”
team in their work for the Hubble constant.
Finally, we explore the possibility to determine rough metallicities of
our cluster dEs from their
colours via Worthey's stellar population synthesis models.
The median metallicities are found in the range from -1.5 to -1 with a concentration
around [Fe/H]
. A comparison with spectral line indices results available for three
galaxies shows good agreement. Moreover, the derived metallicities place the bright Fornax
dEs on the extension of the metallicity–luminosity relation defined by the low luminous Local
Group dEs which provides additional support for the
colour as a useful metallicity
estimator. The data further suggest an age range between 10 and 12 Gyr for the Fornax dwarfs.
Key words: galaxies: clusters: individual: Fornax / galaxies: distances and redshifts / galaxies: dwarf / galaxies: elliptical and lenticular, cD / galaxies: individual: IC1919 / galaxies: stellar content
© ESO, 2003
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