Issue |
A&A
Volume 381, Number 1, JanuaryI 2002
|
|
---|---|---|
Page(s) | 51 - 64 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20011266 | |
Published online | 15 January 2002 |
Confidence levels of evolutionary synthesis models
II. On sampling and Poissonian fluctuations
1
UMR CNRS 5572, Observatoire Midi-Pyrénées, 14, avenue Édouard Belin, 31400 Toulouse, France
2
Centre d'Études Spatiales des Rayonnements, CNRS/UPS, BP 4346, 31028 Toulouse Cedex 4, France
3
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
4
Instituto de Astronomía, UNAM, Apdo. Postal 70-264, 04510 México D.F., Mexico
5
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
6
Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), PO Box 50727, 28080 Madrid, Spain
Corresponding author: M. Cerviño, mcs@laeff.esa.es
Received:
25
April
2001
Accepted:
6
September
2001
In terms of statistical fluctuations, stellar population
synthesis models are only asymptotically correct in the limit of a large
number of stars, where sampling errors become asymptotically small. When
dealing with stellar clusters, starbursts, dwarf galaxies or stellar
populations within pixels, sampling errors introduce a large dispersion in
the predicted integrated properties of these populations. We present here
an approximate but generic statistical formalism which allows a very good
estimation of the uncertainties and confidence levels in any integrated
property, bypassing extensive Monte Carlo simulations, and including the
effects of partial correlations between different observables. Tests of the
formalism are presented and compared with proper estimates. We derive the
minimum mass of stellar populations which is required to reach a given
confidence limit for a given integrated property. As an example of this
general formalism, which can be included in any synthesis code, we apply it
to the case of young ( Myr) starburst populations. We show
that, in general, the UV continuum is more reliable than other continuum
bands for the comparison of models with observed data. We also show that
clusters where more than 105
have been transformed into stars
have a relative dispersion of about 10% in Q(He+) for ages smaller than
3 Myr. During the WR phase the dispersion increases to about 25% for such
massive clusters. We further find that the most reliable observable for
the determination of the WR population is the ratio of the luminosity of
the WR bump over the Hβ luminosity. A fraction of the observed
scatter in the integrated properties of clusters and starbursts can be
accounted for by sampling fluctuations.
Key words: galaxies: starbust / galaxies: evolution / galaxies: statistics / methods: numerical
© ESO, 2002
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.