Distance estimate and progenitor characteristics of SN 2005cs in M51

Abstract

Distance to the Whirlpool Galaxy (M51, NGC 5194) is estimated using published photometry and spectroscopy of the Type II-P supernova SN 2005cs. Both the Expanding Photosphere Method (EPM) and the Standard Candle Method (SCM), suitable for SNe II-P, were applied. The average distance (7.1 \pm 1.2 Mpc) is in good agreement with earlier SBF- and PNLF-based distances, but slightly longer than the distance obtained by Baron et al. for SN 1994I via the Spectral Fitting Expanding Atmosphere Method (SEAM). Since SN 2005cs exhibited low expansion velocity during the plateau phase, similarly to SN 1999br, the constants of SCM were re-calibrated including the data of SN 2005cs as well. The new relation is better constrained in the low velocity regime (v_{ph}(50) ~ 1500 - 2000$ km/s), that may result in better distance estimates for such SNe. The physical parameters of SN 2005cs and its progenitor are re-evaluated based on the updated distance. All the available data support the low-mass (~ 9 M_\odot) progenitor scenario proposed previously by its direct detection with the Hubble Space Telescope.