Astron. Astrophys. 341, 709-724 (1999)
We have compiled from the literature all available data on element
abundances in DLA systems measured over the last decade, referred them
all to one set of oscillator strength and solar reference values and
subdivided them into reliable and less reliable
We extended our chemical galaxy evolution model to calculate
abundances for altogether 16 different elements in spiral galaxies in
a chemically consistent way, i.e. accounting for the steadily
increasing initial metallicities of successive generations of stars by
using input data bases (stellar yields, evolutionary tracks, lifetimes
and remnant masses) for 5 different metallicities from Z = 0
. Dynamical effects, however, are not
included in our simple 1-zone models.
A detailed comparison of model results with observations for eight
different element abundances yields the following main results:
The conformity between observed element abundances in DLA systems
and those calculated from our models for spiral galaxies spanning the
whole redshift range indicates that
DLA galaxies may well evolve into the full range of present-day spiral
Without any adjustments and only using SFHs that proved successful
for the spectrophotometric description of spiral galaxies from zero to
high redshift our models successfully bridge the gap between
abundances observed in high redshift DLA absorbers and the
H II regions of present-day normal spiral galaxies Sa
The slow redshift evolution of DLA abundances (compared to halo CIV
systems) is a consequence of the relatively long timescales for star
formation in disk galaxies.
The large scatter observed in element abundances in DLAs of similar
redshift is naturally explained by the range of star formation rates
at any redshift between early and late type spiral galaxies.
The few observations exceeding the abundances calculated for our Sa
model can be explained either by a temporarily enhanced SFR or a small
starburst in early type spirals if only SNII products are enhanced or
by a shorter characteristic timescale for star formation, very early
star formation enhancement or a local overabundance along the line of
sight if both SNI and SNII products are enhanced.
Comparison of our chemically consistent models with models using
only solar metallicity input physics shows that differences in the
redshift evolution are small for some elements but large for others.
For the elements Zn, Ni and Al with large differences the chemically
consistent models provide a significantly better agreement with
observed DLA abundances.
Using a Salpeter IMF instead of Scalo yields larger element
abundances throughout and many data points fall below the curve of the
Sd model. This could be compensated by using a lower SFR and means
that more DLAs could be LSB galaxies.
Our comparison of element abundances observed in DLA systems with
those resulting from our chemically consistent galaxy evolution models
has important implications for the nature of low redshift DLAs and the
possibility of optical identification of DLAs over the whole redshift
© European Southern Observatory (ESO) 1999
Online publication: December 16, 1998