tokens: (Figure 4 ). Furthermore, we collected emission line fluxes of SLSN host galaxies from the literature (Lunnan et al. 2014 ; Leloudas et al. 2015 ; Perley et al. 2016 ; Chen et al. 2017a , 2017b ) and corrected for foreground and internal dust extinction given by the Balmer decrement. SLSN host galaxies are located predominantly in the high ionization region with log([O iii ]/H β ) > 0.5 for any given [N ii ]/H α . This region is populated by extreme emission line galaxies as Leloudas et al. ( 2015 ) pointed out. The positions of SN 2017egm and PTF 10uhf are in a distinct region of the BPT diagram to most other SLSN hosts. This may indicate that SLSNe extend out to large metallicities than previously believed, and may cover a similar region to gamma-ray burst (GRB) host galaxies (see Figure 8 in Krühler et al. 2015 ). Improved completeness of low-redshift SN samples should indicate if SN 2017egm (and PTF 10uhf) are outliers or at the extreme end of a continuous distribution. 3.4. Stellar Ages and Progenitor Masses of GRBs and SLSNe We used the EW of H α as a tracer of the stellar population age (e.g., Leloudas et al. 2011 ; Kuncarayakti et al. 2016 and references therein). In general, a higher EW H α corresponds to a younger age, though the relation between the EW and age is dependent on the star formation history, initial-mass function, metallicity, and binary or single stellar populations (e.g., Eldridge Stanway 2009 ). We collected the EWs of H α at the explosion sites of SLSNe and GRBs from IFU and resolved long-slit spectroscopy (for references see Table 1 ), and estimated the stellar population ages using consistent models. We applied the Binary Population and Spectral Synthesis (BPASS 11 11 http://bpass.auckland.ac.nz version 2.1 models (Stanway et al. 2016 ; Eldridge et al. 2017 ) in combination with the photoionization Code CLOUDY (e.g., Ferland et al. 2013 ). These models will be described in L. Xiao et al. (2017, in preparation), and have been used to study the ages of SNe in Xiao et al. ( 2017 ). Table 1 Physical Properties Inferred from IFU and Resolved Long-slit Spectroscopy at SLSN and GRB Explosion Sites Note. For consistency, we re-calculate the stellar population age using the BPASS model. References are: (a) this work, (b) Cikota et al. ( 2017 ), (c) Thöne et al. ( 2015 ), (d) Krühler et al. ( 2017 ) (GRB 980425/SN 1998bw), (e) Izzo et al. ( 2017b ) (GRB 100316D/SN 2010bh), (f) Thöne et al. ( 2014 ) (GRB 060505/SN-less), (g) Tanga et al. ( 2017 ) (GRB 111005A/SN-less). To calculate the ages of the stellar populations, we select models that have a [O/H] value closest to that measured at the explosion site using the O3N2 calibration (Table 1 ). For each of the SLSNe we then provide two ages, one assuming the stellar population is comprised of single stars only and the second of binary stars. We see that there is a significant difference in the stellar population ages that we derive depending on the BPASS model used. The
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