HUBBLE SPIES COSMIC DUST
BUNNIES
Like dust bunnies that lurk in corners and under
beds, surprisingly complex loops and blobs of cosmic
dust lie hidden in the giant elliptical galaxy NGC
1316. This image made from data obtained with the
the NASA/ESA Hubble Space Telescope reveals the
dust lanes and star clusters of this giant galaxy
that give evidence that it was formed from a past
merger of two gas-rich galaxies.
The combination of Hubble's superb spatial resolution
and the sensitivity of the Advanced Camera for Surveys
(ACS), installed onboard Hubble in 2002 and used
for these images, enabled uniquely accurate measurements
of a class of red star clusters in NGC 1316. Astronomers
conclude that these star clusters constitute clear
evidence of the occurrence of a major collision
of two spiral galaxies that merged together a few
billion years ago to shape NGC 1316 as it appears
today.
NGC 1316 is on the outskirts of a nearby cluster
of galaxies in the southern constellation of Fornax,
at a distance of about 60 million light years. It
is one of the brightest ellipticals in the Fornax
galaxy cluster. NGC 1316, also known as Fornax A,
is one of the strongest and largest radio sources
in the sky, with radio lobes extending over several
degrees of sky (well off the Hubble image).
NGC 1316's violent history is evident in various
ways. Wide-field imagery from Cerro Tololo Interamerican
Observatory in Chile shows a bewildering variety
of ripples, loops and plumes immersed in the galaxy's
outer envelope. Amongst these so-called "tidal"
features, the narrow ones are believed to be the
stellar remains of other spiral galaxies that merged
with NGC 1316 some time during the last few billion
years. The inner regions of the galaxy shown in
the Hubble image reveal a complicated system of
dust lanes and patches. These are thought to be
the remains of the interstellar medium associated
with one or more of the spiral galaxies swallowed
by NGC 1316.
The U.S. team of scientists, led by Dr. Paul Goudfrooij
of the Space Telescope Science Institute in Baltimore,
Maryland, used the ACS onboard Hubble to study star
clusters in several nearby giant elliptical galaxies.
Their study of NGC 1316 focused on globular clusters,
which are compact stellar systems with hundreds
of thousands to millions of stars formed at the
same time.
The unprecendented sensitivity of the Hubble ACS
data permitted the team to detect faint globular
clusters previously impossible to reach. By counting
the number of globular clusters detected as a function
of their brightness they could, for the first time,
see evidence of the gradual disruption of star clusters
created during a past merger of gas-rich galaxies.
They found that the relative number of low-mass
clusters is significantly lower in the inner regions
than in the outer regions, by an amount consistent
with theoretical predictions.
These Hubble ACS images were taken in March 2003.
The color composite is a combination of data taken
in blue, visible, and infrared filters. The team's
results have improved our understanding of how elliptical
galaxies and their star clusters may have formed
during galaxy mergers and then evolve to resemble
'normal' elliptical galaxies after several billions
of years.
Credit: NASA, ESA, and The Hubble Heritage Team
(STScI/AURA)
Acknowledgment: P. Goudfrooij (STScI) |
