Figure 1. GMOS-South image of the center of the Abell 85 galaxy cluster.
The brightest galaxy in the middle was thought to hide a supermassive
black hole in its core based on prior lower-resolution data.
Figure 2. Surface brightness profile of the brightest cluster galaxy in
Abell 85. The top panel presents the light emanating from that galaxy in
the inner 6 kiloparsecs. The new Gemini data show a light excess,
visible as a bump in the very center of the profile. In contrast,
earlier observations (black) had suggested a light deficit at the core,
but this is an artifact of their lower resolution.
Research shows that supermassive black holes like to be the only
residents on the block, as stars too close to them end up being thrown
vast distances from the galaxy's center. As black holes eject stars
around them, the neighborhood becomes darker. Astronomers have been
hunting for these gloomy neighborhoods in galaxy cores for decades. The
signature of supermassive black holes are known as light deficits, due
to the lack of stars surrounding them.
Gemini Science Fellow, Juan Madrid and Carlos Donzelli from the Cordoba
observatory in Argentina were granted observations through the
Director's Discretionary Time, and used new Gemini data to study the
brightest galaxy of the galaxy cluster Abell 85 to verify earlier
observations hinting that one of the most supermassive black holes ever
discovered resided at the galaxy's core.
Gemini sets the record straight - in seven minutes
The Gemini Multi Object Spectrograph (GMOS) at Gemini South
needed only seven minutes of observations to reveal that the brightest
galaxy of Abell 85 does not have a light deficit. On the contrary, the
high resolution of the Gemini data show that the core of this galaxy has
a light excess incompatible with the theory that it hosts an especially
massive black hole.
Paper Abstract:
New high-resolution r band imaging of the brightest
cluster galaxy (BCG) in Abell 85 (Holm 15A) was obtained using the
Gemini Multi Object Spectrograph. These data were taken with the aim of
deriving an accurate surface brightness profile of the BCG of Abell 85,
in particular its central region. The new Gemini data show clear
evidence of a previously unreported nuclear emission that is evident as a
distinct light excess in the central kiloparsec of the surface
brightness profile. We find that the light profile is never flat nor
does it present a downward trend towards the center of the galaxy. That
is, the new Gemini data show a different physical reality from the
featureless, "evacuated core" recently claimed for the Abell 85 BCG.
After trying different models, we find that the surface brightness
profile of the BCG of Abell 85 is best fit by a double Sérsic model.
Source: Gemini Observatory
