First release of high-redshift superluminous supernovae from the Subaru HIgh-Z sUpernova CAmpaign (SHIZUCA). II. Spectroscopic properties

TL;DR

This paper reports spectroscopic observations of three high-redshift superluminous supernovae from the SHIZUCA campaign, confirming their redshifts and demonstrating the effectiveness of the survey in identifying distant SLSNe for detailed follow-up.

Contribution

It provides the first Keck spectroscopic data of high-redshift SLSNe from SHIZUCA, confirming redshifts and showcasing the survey's capability for rapid, accurate identification.

Findings

Confirmed redshifts of 1.851, 1.965, and 2.399 for three SLSNe.

Spectra show significant host galaxy flux, complicating supernova classification.

Demonstrated SHIZUCA's effectiveness in high-redshift SLSN detection.

Abstract

We present Keck spectroscopic observations of three probable high redshift superluminous supernovae (SLSNe) from the Subaru HIgh-Z sUpernova CAmpaign (SHIZUCA), confirming redshifts of 1.851, 1.965 and 2.399. The host galaxies were selected for transient monitoring from multi-band photometric redshifts. The supernovae are detected during their rise, and the classically scheduled spectra are collected near maximum light. The restframe far-ultraviolet (FUV;$\sim$1000A-2500A) spectra include a significant host galaxy flux contribution and we compare our host galaxy subtracted spectra to UV-luminous SNe from the literature. While the signal-to-noise ratios of the spectra presented here are sufficient for redshift confirmation, supernova spectroscopic type confirmation remains inconclusive. The success of the first SHIZUCA Keck spectroscopic follow-up program demonstrates that campaigns such as SHIZUCA are capable of identifying high redshift SLSNe with sufficient accuracy, speed and depth for rapid, well-cadenced and informative follow-up.