Misc,
The Vulture Survey I: Analyzing the Evolution of $\MgII$ Absorbers
(2017)cite arxiv:1701.05624Comment: 15 pages, 10 figures.
Abstract
We present detailed measurements of the redshift path density, equivalent
width distribution, column density distribution, and redshift evolution of
$\MgII$ absorbers as measured in archival spectra from the UVES spectrograph
at the Very Large Telescope (VLT/UVES) and the HIRES spectrograph at the Keck
Telescope (Keck/HIRES) to equivalent width detection limits below $0.01$~\AA.
This survey examines 432 VLT/UVES spectra from the UVES SQUAD collaboration and
170 Keck/HIRES spectra from the KODIAQ group, allowing for detections of
intervening $\MgII$ absorbers spanning redshifts $0.1 < z < 2.6$. We employ
an accurate, automated approach to line detection which consistently detects
redshifted absorption lines. We measure the equivalent widths, apparent optical
depth column densities, and velocity widths for each absorbing system. Using
our complete sample of all detectable $\MgII$ absorbers, we can accurately
determine the redshift path density of absorbers across cosmic time. We measure
evolution in the comoving $\MgII$ line density, $dN\,/dX$, finding more high
equivalent width absorbers at $z = 2$ than at present. We also measure
evolution in the equivalent width distribution, parameterized by a Schechter
function fit, finding a shallower weak-end slope for absorbers at redshifts
between $1.53 < z < 2.64$ as compared to lower redshifts. Finally, we calculate
the cosmic mass fraction of $\MgII$ using the column density distribution. We
find that weak $\MgII$ absorbers, those with equivalent widths less than
$0.3$~\AA, are physically distinct and evolve separately from very strong
$\MgII$ absorbers, which have equivalent widths greater than $1.0$~\AA.
