Effects of a central dark matter core on time-delay cosmography with galaxy clusters

Abstract

The central dark matter distribution probes the nature of dark matter and baryon physics, yet its impact on time-delay cosmography is not fully explored. We update previous analyses of the cluster-lensed quasar SDSS J1004+4112 and the supernova Refsdal in MACS J1149.5+2223 by replacing the main halo density profile from an elliptical Navarro-Frenk-White (NFW) profile to a cored elliptical NFW profile and investigating the impact of the central dark matter core on the Hubble constant $H_0$. We jointly infer $H_0$ and the dimensionless core size parameter $β=r_{\rm c}/r_{\rm s}$, while the Brightest Cluster Galaxy (BCG) is either tied to the scaling relation of cluster member galaxies or modeled separately, with its mass left free or assigned a Gaussian prior from the stellar mass estimate for a Chabrier or Salpeter initial mass function (IMF). For SDSS J1004+4112, constraints on both $β$ and $H_0$ strongly depend on the treatment of the BCG. A large core is implied when no prior is added to the BCG stellar mass, while a reasonable assumption on the BCG mass prefers a nearly cuspy halo with $β\sim 10^{-3}$. For MACS J1149.5+2223, a large core of $β\sim 0.5$ is obtained with no prior, while a modest core of $β=0.0410^{+0.0865}_{-0.0276}$ is preferred when the Salpeter IMF is assumed. The constraint on $H_0$ from MACS J1149.5+2223 is stable against the BCG treatment, supporting its robustness. For the Salpeter-prior case, we obtain $H_0=65.9^{+3.5}_{-3.4}\mathrm{~km~s^{-1}~Mpc^{-1}}$, and different BCG assumptions change the median $H_0$ by less than $1σ$. The core size constraints are translated into the self-interacting dark matter cross section, giving a 95% upper limit of $σ/m<0.035\,\mathrm{cm}^{2}\,\mathrm{g}^{-1}$ from SDSS J1004+4112 and the 68% range of $σ/m=0.071^{+0.15}_{-0.045}\,\mathrm{cm}^{2}\,\mathrm{g}^{-1}$ from MACS J1149.5+2223.