Taking stock of SLSN and LGRB host galaxy comparison using a complete sample of LGRBs

TL;DR

This study compares host galaxy properties of hydrogen-poor SLSNe and LGRBs at intermediate redshifts, finding similar characteristics and challenging previous claims of differences at lower redshifts.

Contribution

It provides a complete, methodologically consistent comparison of SLSN and LGRB host galaxies, addressing previous sample biases and focusing on intermediate redshift ranges.

Findings

Host galaxy properties do not differ significantly at 0.3 < z < 0.7.

Both classes follow the fundamental metallicity relation.

Emission line equivalent widths are similar for both populations.

Abstract

Long gamma-ray bursts (LGRBs) and superluminous supernovae (SLSNe) are both explosive transients with very massive progenitor stars. Clues about the nature of the progenitors can be found by investigating environments in which such transients occur. While studies of LGRB host galaxies have a long history, dedicated observational campaigns have only recently resulted in a high enough number of photometrically and spectroscopically observed SLSN hosts to allow statistically significant analysis of their properties. In this paper we make a comparison of the host galaxies of hydrogen-poor (H-poor) SLSNe and the Swift/BAT6 sample of LGRBs. In contrast to previous studies we use a complete sample of LGRBs and we address a special attention to the comparison methodology and the selection of SLSN sample whose data have been compiled from the available literature. At intermediate redshifts (0.3 < z < 0.7) the two classes of transients select galaxies whose properties (stellar mass, luminosity, star-formation rate, specific star-formation rate and metallicity) do not differ on average significantly. Moreover, the host galaxies of both classes of objects follow the fundamental metallicity relation and the fundamental plane of metallicity. In contrast to previous studies we show that at intermediate redshifts the emission line equivalent widths of the two populations are essentially the same and that the previous claims regarding the higher fraction of SLSN hosts among the extreme emission line galaxies with respect to LGRBs are mostly due to a larger fraction of strong-line emitters among SLSN hosts at z < 0.3, where samples of LGRB hosts are small and poorly defined.