# Star formation, supernovae, iron, and $α$: consistent cosmic and Galactic histories [HEAP]

Recent versions of the observed cosmic star-formation history (SFH) have resolved an inconsistency between the SFH and the observed cosmic stellar mass density history. Here, we show that the same SFH revision scales up by a factor $\sim 2$ the delay-time distribution (DTD) of Type Ia supernovae (SNe Ia), as determined from the observed volumetric SN Ia rate history, and thus brings it into line 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 SN Ia production efficiency of $N/M_\star=1.25\pm 0.10$ SNe Ia per $1000~{\rm M_\odot}$ of formed stellar mass. Using these revised histories and updated, purely empirical, iron yields of the various SN types, we rederive 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, as deduced also for the Sun. We find the track of the average cosmic gas element in the [$\alpha$/Fe] vs. [Fe/H] abundance-ratio plane, as well as the track for gas in galaxy clusters, which have a higher DTD and have had a distinct, burst-like, SFH. Our cosmic $[\alpha$/Fe] vs. [Fe/H] 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, and we find a MW SFH that makes the track closely match the stellar locus. The cluster DTD with a short-burst SFH at $z=3$ produces a track that matches well the observed `high-$\alpha$’ locus of MW stars, suggesting the halo/thick-disk population has had a galaxy-cluster-like formation history.

D. Maoz and O. Graur
Thu, 16 Mar 17
13/92