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 I _ { \circ } ^ { { TRGB } } = 26.65 \pm 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 ) } _ { \circ } = 30.62 \pm 0.17 corresponding to a distance of 13.3 \pm 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 .