Issue |
A&A
Volume 448, Number 3, March IV 2006
|
|
---|---|---|
Page(s) | 955 - 970 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20053763 | |
Published online | 03 March 2006 |
The chemical composition of metal-poor emission-line galaxies in the Data Release 3 of the Sloan Digital Sky Survey
1
Main Astronomical Observatory, Ukrainian National Academy of Sciences, Zabolotnoho 27, Kyiv 03680, Ukraine e-mail: izotov@mao.kiev.ua
2
LUTH, Observatoire de Meudon, 92195 Meudon Cedex, France
3
Geneva Observatory, 1290 Sauverny, Switzerland
4
Astronomy Department, University of Virginia, Charlottesville, VA 22903, USA
Received:
5
July
2005
Accepted:
15
November
2005
We have re-evaluated empirical expressions for the abundance
determination of N, O, Ne, S, Cl, Ar and Fe taking into account the latest
atomic data and constructing an appropriate grid of photoionization models
with state-of-the art model atmospheres. Using these expressions
we have derived heavy element abundances in the ~310 emission-line
galaxies from the Data Release 3 of the Sloan Digital Sky Survey (SDSS)
with an observed Hβ flux F(Hβ) >
10-14 erg s-1 cm-2 and for which the [O iii]
λ4363 emission line was detected at least at a 2σ level,
allowing abundance determination by direct methods.
The oxygen abundance 12 + log O/H of the
SDSS galaxies lies in the range from ~7.1 (/30) to
~8.5 (0.7
). The SDSS sample is merged with a sample of 109
blue compact dwarf (BCD) galaxies with high quality spectra, which contains
extremely low-metallicity objects. We use the merged sample to study the
abundance patterns of low-metallicity emission-line galaxies.
We find that extremely metal-poor galaxies (12 + log O/H < 7.6, i.e. Z <
/12) are rare in the SDSS sample. The α element-to-oxygen
abundance ratios do not show
any significant trends with oxygen abundance, in agreement with previous
studies, except for a slight increase of Ne/O with increasing metallicity,
which we interpret as due to a moderate depletion of O onto grains in the most
metal-rich galaxies. The Fe/O abundance ratio is smaller than the solar value,
by up to 1 dex at the high metallicity end. We also find that Fe/O increases
with decreasing Hβ equivalent width EW(Hβ). We interpret this as
a sign of strong depletion onto dust grains, and gradual destruction of those
grains on a time scale of a few Myr.
All the galaxies are found to have log N/O > –1.6, implying that they
have a different nature than the subsample of
high-redshift damped Lyα systems with
log N/O of ~–2.3 and that their ages are
larger than 100–300 Myr. We confirm the apparent increase in N/O with
decreasing EW(Hβ), already shown in previous studies, and explain it as the
signature of gradual nitrogen ejection by massive stars from the most recent
starburst.
Key words: galaxies: ISM / galaxies: starburst / galaxies: abundances
© ESO, 2006
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.