A new red giant-based distance modulus of 13.3 Mpc to the Antennae galaxies and its consequences
Authors: Ivo Saviane (1), Yazan Momany (2), Gary S. Da Costa (3), R. Michael Rich (4), John Hibbard (5) ((1) ESO, Santiago, Chile, (2) Astronomical Observatory, Padova, Italy, (3)RSAA, ANU, Australia, (4) Physics and Astronomy Department, UCLA, USA, (5) NRAO, Charlottesville, USA)
(Submitted on 7 Feb 2008)
"Abstract: The Antennae galaxies are the closest example of an ongoing major galaxy merger, and thereby represent a unique laboratory for furthering the understanding of the formation of exotic objects (e.g., tidal dwarf galaxies, ultra-luminous X-ray sources, super-stellar clusters, etc). In a previous paper HST/WFPC2 observations were used to demonstrate that the Antennae system might be at a distance considerably less than that conventionally assumed in the literature. Here we report new, much deeper HST/ACS imaging that resolves the composite stellar populations, and most importantly, reveals a well-defined red giant branch. The tip of this red giant branch (TRGB) is unambiguously detected at Io(TRGB)=26.65 +/- 0.09 mag. Adopting the most recent calibration of the luminosity of the TRGB then yields a distance modulus for the Antennae of (m-M)o= 30.62 +/- 0.17 corresponding to a distance of 13.3 +/- 1.0 Mpc. This is consistent with our earlier result, once the different calibrations for the standard candle are considered. We briefly discuss the implications of this now well determined shorter distance. "
The "canonical" distance was 20-30 Mpc based on redshift.
The mainstream authors discuss the consequences of this drastically reduced distance in terms of object size, mass function, cluster life etc.
But the 800 pound gorilla: why such a difference between TRGB and redshift distance? is modestly ignored. Is there a reason why I should not be surprised?

http://arxiv.org/abs/0802.1045v1