Abstract
We investigate the variation of the ratio of the equivalent widths of the
FeII$łambda$2600 line to the MgII$łambdałambda$2796,2803 doublet as a
function of redshift in a large sample of absorption lines drawn from the
JHU-SDSS Absorption Line Catalog. We find that despite large scatter, the
observed ratio shows a trend where the equivalent width ratio
$RW_FeII/W_MgII$ decreases monotonically with
increasing redshift $z$ over the range $0.55 z 1.90$. Selecting the
subset of absorbers where the signal-to-noise ratio of the MgII equivalent
width $W_MgII\ge$3 and modeling the equivalent width ratio distribution
as a gaussian, we find that the mean of the gaussian distribution varies as
$R(-0.045\pm0.005)z$. We discuss various possible reasons for
the trend. A monotonic trend in the Fe/Mg abundance ratio is predicted by a
simple model where the abundances of Mg and Fe in the absorbing clouds are
assumed to be the result of supernova ejecta and where the cosmic evolution in
the SNIa and core-collapse supernova rates is related to the cosmic
star-formation rate. If the trend in $R$ reflects the evolution in
the abundances, then it is consistent with the predictions of the simple model.
Users
Please
log in to take part in the discussion (add own reviews or comments).