Zooming In on the Progenitors of Superluminous Supernovae With HST

R. Lunnan, R. Chornock, E. Berger, A. Rest, W. Fong, D. Scolnic, D. Jones, A. M. Soderberg, P. M. Challis, M. R. Drout, R. J. Foley, M. E. Huber, R. P. Kirshner, C. Leibler, G. H. Marion, M. McCrum, D. Milisavljevic, G. Narayan, N. E. Sanders, S. J. Smartt, K. W. Smith, J. L. Tonry, W. S. Burgett, K. C. Chambers, H. Flewelling, R. -P. Kudritzki, R. J. Wainscoat, C. Waters

Published 2014-11-04Version 1

We present Hubble Space Telescope rest-frame ultraviolet imaging of the host galaxies of 16 hydrogen-poor superluminous supernovae (SLSNe), including 11 events from the Pan-STARRS Medium Deep Survey. Taking advantage of the superb angular resolution of HST, we characterize the galaxies' morphological properties, sizes and star formation rate densities. We determine the SN locations within the host galaxies through precise astrometric matching, and measure physical and host-normalized offsets, as well as the SN positions within the cumulative distribution of UV light pixel brightness. We find that the host galaxies of H-poor SLSNe are irregular, compact dwarf galaxies, with a median half-light radius of just 0.9 kpc. The UV-derived star formation rate densities are high (<Sigma_SFR> ~ 0.1 M_sun/yr/kpc^2), suggesting that SLSNe form in overdense environments. Their locations trace the UV light of their host galaxies, with a distribution intermediate between that of LGRBs (which are strongly clustered on the brightest regions of their hosts) and a uniform distribution (characteristic of normal core-collapse SNe). Taken together, this strengthens the picture that SLSN progenitors require different conditions than those of ordinary core-collapse SNe to form, and that they explode in broadly similar galaxies as do LGRBs. However, the locations of SLSNe are less clustered on the brightest regions than are LGRBs, suggesting a different and potentially lower-mass progenitor population for SLSNe than LGRBs.