Issue |
A&A
Volume 505, Number 2, October II 2009
|
|
---|---|---|
Page(s) | 483 - 495 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/200810320 | |
Published online | 11 August 2009 |
The age of blue LSB galaxies*
1
The Institute for Computational Astrophysics, Saint Mary's University, Halifax NS, B3H 3C3, Canada
2
Institute of Physics, South Federal University, Stachki 194, Rostov-on-Don, Russia e-mail: eduard_vorobev@mail.ru
3
Astronomisches Institut, Ruhr-Universität Bochum, Bochum, Germany
4
New Mexico State University/APO, Sunspot, NM, 88349, USA
5
Sternberg Astronomical Institute, Universitetsky 13, Moscow 119992, Russia
Received:
3
June
2009
Accepted:
15
June
2009
Context. Low metallicities, high gas-to-star mass ratios, and blue colors of most low surface brightness (LSB) galaxies imply that these systems may be younger than their high surface brightness counterparts.
Aims. We look for observational signatures that can help to constrain the age of blue LSB galaxies.
Methods. We use numerical hydrodynamic modelling to study the long-term (∼13 Gyr)
dynamical and chemical
evolution of blue LSB galaxies, adopting a sporadic scenario of star formation.
Our model galaxy consists of a thin gas disk, a stellar disk with a developed spiral structure
and a spherical dark matter halo. Our models utilize various rates of
star formation and different shapes of the initial mass function (IMF).
We complement hydrodynamic modelling with population synthesis modelling to produce
the integrated colors and Hα equivalent widths.
Results. We find that the mean oxygen abundances, colors, Hα equivalent widths,
and the radial fluctuations
in the oxygen abundance, when considered altogether, can be used to constrain the age of blue
LSB galaxies if some independent knowledge of the IMF is available.
Our modelling strongly suggests the existence of a minimum age for
blue LSB galaxies. Model
colors and mean oxygen abundances
set a tentative minimum age at 1.5–3.0 Gyr, whereas model Hα equivalent widths
suggest a larger value of the order of 5–6 Gyr. The latter value may decrease somewhat if blue LSB
galaxies host IMFs with a truncated upper mass limit. We found no firm evidence that
the age of blue LSB galaxies is significantly lower than 13 Gyr.
Conclusions. The age of blue LSB galaxies may vary between 1.5–6 Gyr and 13 Gyr, depending on the physical conditions in the disk that control the form of the IMF and the rate of star formation. A failure to observationally detect large radial fluctuations in the oxygen abundance of the order of 0.5–1.0 dex, which, according to our modelling, are characteristic of (1–2)-Gyr-old galaxies, will argue in favour of the more evolved nature of blue LSB galaxies.
Key words: ISM: abundances / galaxies: abundances / galaxies: evolution
© ESO, 2009
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