An international team of researchers led by Aaron Romanowsky of San
José State University has used the Subaru Telescope to identify a faint
dwarf galaxy disrupting around a nearby giant spiral galaxy. The
observations provide a valuable glimpse of a process that is fleeting
but important in shaping galaxies.
"The outer regions of giant galaxies like our own Milky Way appear to
be a jumble of debris from hundreds of smaller galaxies that fell in
over time and splashed into smithereens," said Romanowsky. "These dwarfs
are considered building blocks of the giants, but the evidence for
giants absorbing dwarfs has been largely circumstantial. Now we have
caught a pair of galaxies in the act of a deadly embrace." (Figure 1)
The two objects in the study are NGC 253, also called the Silver
Dollar galaxy, and the newly discovered dwarf NGC 253-dw2. They are
located in the Southern constellation of Sculptor at a distance of 11
million light years from Earth, and are separated from each other by
about 160 thousand light years. The dwarf has an elongated appearance
that is the hallmark of being stretched apart by the gravity of a larger
galaxy.
The dwarf has been trapped by its giant host and will not survive
intact for much longer," said team member Nicolas Martin, of the
Strasbourg Observatory. "The next time it plunges closer to its host, it
could be shredded into oblivion. However, the host may suffer some
damage too, if the dwarf is heavy enough."
The interplay between the two galaxies may resolve an outstanding
mystery about NGC 253, as the giant spiral shows signs of being
disturbed by a dwarf. The disturber was previously unseen and presumed
to have perished, but now the likely culprit has been found. "This looks
like a case of galactic stealth attack," said Gustavo Morales of
Heidelberg University. "The dwarf galaxy has dived in from the depths of
space and barraged the giant, while remaining undetected by virtue of
its extreme faintness."
The discovery of NGC 253-dw2 has an unusual pedigree. It began with a
digital image of the giant galaxy taken by astrophotographer Michael
Sidonio using a 30 centimeter (12 inch) diameter amateur telescope in
Australia. Other members of the international team noticed a faint
smudge in the image and followed it up with a larger, 80 centimeter (30
inch) amateur telescope in Chile, led by Johannes Schedler. The identity
of the object was still not clear, and it was observed with the 8 meter
(27 foot) Subaru Telescope on the summit of Mauna Kea in Hawaii, in
December 2014. "In the first image, we weren't sure if there was really a
faint galaxy or if it was some kind of stray reflection," said David
Martínez-Delgado, also from Heidelberg University. "With the
high-quality imaging of the Suprime-Cam instrument on the Subaru
Telescope, we can now see that the smudge is composed of individual
stars and is a bona fide dwarf galaxy. This discovery is a wonderful
example of fruitful collaboration between amateur and professional
astronomers." (Figure 2)
Figure 2: Close-up view of the dwarf galaxy NGC
253-dw2. The closely packed red dots show that it is composed of
individual stars. Click here
for the original tiff file. (Image credit: Copyright © 2015 R. Jay
GaBany (Cosmotography.com), Zachary Jennings (University of California,
Santa Cruz), and National Astronomical Observatory of Japan (NAOJ)).
The findings are in research paper published in the Monthly Notices
of the Royal Astronomical Society Letters by Oxford University Press, as
"Satellite accretion in action: a tidally disrupting dwarf spheroidal
around the nearby spiral galaxy NGC 253" by Romanowsky et al., first
online on January 23, 2016 (http://mnrasl.oxfordjournals.org/lookup/doi/10.1093/mnrasl/slv207).
The research team:
- Aaron J. Romanowsky (San José State University and University of California Observatories, USA)
- David Martínez-Delgado (Zentrum für Astronomie der Universität Heidelberg, Germany)
- Nicolas F. Martin (Université de Strasbourg, France and Max-Planck-Institut für Astronomie, Germany)
- Gustavo Morales (Zentrum für Astronomie der Universität Heidelberg, Germany)
- Zachary G. Jennings (University of California, USA)
- R. Jay GaBany (Black Bird Observatory II, USA)
- Jean P. Brodie (University of California Observatories and University of California, USA)
- Eva K. Grebel (Zentrum für Astronomie der Universität Heidelberg, Germany)
- Johannes Schedler (Cerro Tololo Inter-American Observatory, Chile)
- Michael Sidonio (Terroux Observatory, Australia)
Links:
- http://subarutelescope.org/Pressrelease/2014/07/01/index.html
- http://subarutelescope.org/Pressrelease/2012/02/08/index.htmll
Source: Subaru Telescope
