Star formation, supernovae, iron, and alpha: consistent cosmic and
  Galactic histories
  Recent versions of the observed cosmic star-formation history (SFH) have
resolved an inconsistency with the stellar mass density history. We show that
the revised SFH also scales up the delay-time distribution (DTD) of Type Ia
supernovae (SNe Ia), as determined from the observed volumetric SN Ia rate
history, aligning it with other field-galaxy SN Ia DTD measurements. The
revised-SFH-based DTD has a $t^{-1.1 \pm 0.1}$ form and a
Hubble-time-integrated production efficiency of $N/M_\star=1.3\pm0.1$ SNe Ia
per $1000~{\rm M_\odot}$ of formed stellar mass. Using these revised histories
and updated empirical iron yields of the various SN types, we re-derive the
cosmic iron accumulation history. Core-collapse SNe and SNe Ia have contributed
about equally to the total mass of iron in the Universe today. We find the
track of the average cosmic gas element in the [$\alpha$/Fe] vs. [Fe/H]
abundance-ratio plane. The track is broadly similar to the observed main locus
of Galactic stars in this plane, indicating a Milky Way (MW) SFH similar in
form to the cosmic one. We easily find a simple MW SFH that makes the track
closely match this stellar locus. Galaxy clusters appear to have a
higher-normalization DTD. This cluster DTD, combined with a short-burst MW SFH
peaked at $z=3$, produces a track that matches remarkably well the observed
"high-$\alpha$" locus of MW stars, suggesting the halo/thick-disk population
has had a galaxy-cluster-like formation mode. Thus, a simple two-component SFH,
combined with empirical DTDs and SN iron yields, suffices to closely reproduce
the MW's stellar abundance patterns.
