A composite image of the galaxy NGC 1512, located 38 million light years away in the direction of the constellation of Horologium, in the southern hemisphere of the sky. The image shows the regions of unusual chemical enrichment that demonstrate that NGC 1512 has absorbed other galaxies earlier in its history. Credit: Angel R. Lopez-Sanchez (AAO / MQU), & Baerbel Koribalski (CSIRO / CASS). Click here for a full size image
A team of Australian and Spanish astronomers have caught a greedy
galaxy gobbling on its neighbours and leaving crumbs of evidence about
its dietary past.
Galaxies grow by churning loose gas from their surroundings into new
stars, or by swallowing neighbouring galaxies whole. However, they
normally leave very few traces of their cannibalistic habits.
A study published today in Monthly Notices of the Royal Astronomical Society
not only reveals a spiral galaxy devouring a nearby compact dwarf
galaxy, but shows evidence of its past galactic snacks in unprecedented
detail.
Australian Astronomical Observatory (AAO) and Macquarie University astrophysicist, Ángel R. López-Sánchez, and his collaborators have been studying the galaxy NGC 1512 to see if its chemical story matches its physical appearance.
The team of researchers used the unique capabilities of the 3.9-metre Anglo-Australian Telescope
(AAT), near Coonabarabran, New South Wales, to measure the level of
chemical enrichment in the gas across the entire face of NGC 1512.
Chemical enrichment occurs when stars churn the hydrogen and helium
from the Big Bang into heavier elements through nuclear reactions at
their cores.
These new elements are released back into space when the stars die,
enriching the surrounding gas with chemicals like oxygen, which the team
measured.
“We were expecting to find fresh gas or gas enriched at the same
level as that of the galaxy being consumed, but were surprised to find
the gases were actually the remnants of galaxies swallowed earlier,” Dr
López-Sánchez said.
“The diffuse gas in the outer regions of NGC 1512 is not the pristine
gas created in the Big Bang but is gas that has already been processed
by previous generations of stars.”
The Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia Telescope Compact Array (ATCA),
a powerful 6-km diameter radio interferometer (an array of radio
antennas that effectively act as a larger single instrument) located in
eastern Australia, was used to detect large amounts of cold hydrogen gas
that extends way beyond the stellar disk of the spiral galaxy NGC 1512.
"The dense pockets of hydrogen gas in the outer disk of NGC 1512
accurately pin-point regions of active star formation", said CSIRO's Dr
Baerbel Koribalski, a member of the research collaboration.
When this finding was examined in combination with radio and
ultraviolet observations the scientists concluded that the rich gas
being processed into new stars did not come from the inner regions of
the galaxy either. Instead, the gas was likely absorbed by the galaxy
over its lifetime as NGC 1512 accreted other, smaller galaxies around
it.
Dr Tobias Westmeier, from the International Centre for Radio Astronomy Research
in Perth, said that while galaxy cannibalism has been known for many
years, this is the first time that it has been observed in such fine
detail.
“By using observations from both ground and space based telescopes we
were able to piece together a detailed history for this galaxy and
better understand how interactions and mergers with other galaxies have
affected its evolution and the rate at which it formed stars,” he said.
The team’s successful and novel approach to investigating how
galaxies grow is being used in a new program to further refine the best
models of galaxy evolution.
For this work the astronomers used spectroscopic data from the AAT at
Siding Spring Observatory in Australia to measure the chemical
distribution around the galaxies. They identified the diffuse gas around
the dual galaxy system using ATCA radio observations.
In addition, they identified regions of new star formation with data from the Galaxy Evolution Explorer (GALEX) orbiting space telescope.
“The unique combination of these data provide a very powerful tool to
disentangle the nature and evolution of galaxies,” said Dr
López-Sánchez.
“We will observe several more galaxies using the same proven
techniques to improve our understanding of the past behaviour of
galaxies in the local Universe.”
Media contacts
Dr Amanda Bauer
Australian Astronomical Observatory (AAO)
Tel: +61 2 9372 4852
Mob: +61 447 029 368
amanda.bauer@aao.gov.au
Pete Wheeler
The International Centre for Radio Astronomy Research (ICRAR)
Tel: +61 8 6488 7758
Mob: +61 0423 982 018
pete.wheeler@icrar.org
Media contacts
Dr Amanda Bauer
Australian Astronomical Observatory (AAO)
Tel: +61 2 9372 4852
Mob: +61 447 029 368
amanda.bauer@aao.gov.au
Pete Wheeler
The International Centre for Radio Astronomy Research (ICRAR)
Tel: +61 8 6488 7758
Mob: +61 0423 982 018
pete.wheeler@icrar.org
Science contacts
Dr Ángel R. López-Sánchez
Australian Astronomical Observatory / Macquarie University
Tel: +61 2 9372 4898
angel.lopezsanchez@aao.gov.au
Dr Tobias Westmeier
The International Centre for Radio Astronomy Research / University of
Western Australia
Tel: +61 8 6488 4592
tobias.westmeier@icrar.org
Dr Baerbel Koribalski
Commonwealth Scientific and Industrial Research Organisation (CSIRO)
Tel: +61 293 724 361
baerbel.koribalski@csiro.au
Further information
The new work is published in “Ionized gas in the XUV disc of the NGC1512/1510 system”,
Á. R. López-Sánchez, T. Westmeier, C. Esteban, and B. S. Koribalski, Monthly Notices of the Royal Astronomical Society, Oxford University Press, vol. 450 no. 4, pp. 3381-3409, 2015.
Notes for editors
The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3800 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others. Follow the RAS on Twitter.
