A New Distance to The Antennae Galaxies (NGC 4038/39) Based on the Type Ia Supernova 2007sr

Understand

Traditionally, the distance to NGC 4038/39 has been derived from the systemic recession velocity, yielding about 20 Mpc for H_0 = 72 km/s/Mpc.

• Recently, this widely adopted distance has been challenged based on photometry of the presumed tip of the red giant branch (TRGB), which seems to yield a shorter distance of 13.3+-1.0 Mpc and, with it, nearly 1 mag lower luminosities and smaller radii for objects in this prototypical merger.
• Here we present a new distance estimate based on observations of the Type Ia supernova (SN) 2007sr in the southern tail, made at Las Campanas Observatory as part of the Carnegie Supernova Project.
• The resulting distance of D(SN Ia) = 22.3+-2.8 Mpc [(m-M)_0 = 31.74+-0.27 mag] is in good agreement with a refined distance estimate based on the recession velocity and the large-scale flow model developed by Tonry and collaborators, D(flow) = 22.5+-2.8 Mpc.