Ultraluminous supernovae as a new probe of the interstellar medium in distant galaxies

We present the Pan-STARRS1 discovery and light curves, and follow-up MMT and Gemini spectroscopy of an ultraluminous supernova (ULSN; dubbed PS1-11bam) at a redshift of z = 1.566 with a peak brightness of M_UV ≈ −22.3 mag. PS1-11bam is one of the highest redshift spectroscopically confirmed SNe known to date. The spectrum exhibits broad absorption features typical of previous ULSNe (e.g., C ii, Si iii), and strong and narrow Mg ii and Fe ii absorption lines from the interstellar medium (ISM) of the host galaxy, confirmed by an [O ii]λ3727 emission line at the same redshift. The equivalent widths of the Fe ii λ2600 and Mg ii λ2803 lines are in the top quartile of the quasar intervening absorption system distribution, but are weaker than those of gamma-ray burst intrinsic absorbers (i.e., GRB host galaxies). We also detect the host galaxy in pre-explosion Pan-STARRS1 data and find that its UV spectral energy distribution is best fit with a young stellar population age of τ* ≈ 15–45 Myr and a stellar mass of M* ≈ (1.1–2.6) × 10⁹ M☉ (for Z = 0.05–1 Z☉). The star formation rate inferred from the UV continuum and [O ii]λ3727 emission line is ≈10 M☉ yr⁻¹, higher than in previous ULSN hosts. PS1-11bam provides the first direct demonstration that ULSNe can serve as probes of the ISM in distant galaxies. The depth and red sensitivity of PS1 are uniquely suited to finding such events at cosmologically interesting redshifts (z ∼ 1–2); the future combination of LSST and 30 m class telescopes promises to extend this technique to z ∼ 4.