Imaging a galaxy’s molecular outflow

A Hubble image of the merging galaxies NGC 6240. Like other
luminous mergers, this one hosts a rapid flow of molecular
gas. Astronomers have now imaged the carbon monoxide gas in
the central regions and found it forms jet-like outflows
driven by activity around the black holes. Credit: NASA/HST

A merger between galaxies can trigger can intense radiation
from bursts star formation and from the accretion of gas onto
the two supermassive black holes at their centers.
Astronomers have observed a strong statistical correlation
between the masses of these black holes and other properties
of the galaxies like their velocity structure or luminosity,
and have concluded that there must be a connection.

Feedback of some kind seems most likely to explain these
correlations, and astronomers have been working to identify its
source and nature. One prominent suggestion for feedback is an
outflow of molecular gas; once turned on, it would deplete the
galaxy of the raw material needed for making new stars and from
further enhancing the black hole’s mass. Evidence for molecular
outflows has been reported in far infrared lines of molecules,
but these spectral results lack the convincing spatial
information needed to associate the activity with the nuclei

CfA Junko Ueda is a member of a team
of fifteen astronomers who used the ALMA submillimeter
telescope facility, with its superb spatial imaging
capabilities, to study the outflow in the luminous galaxy
NGC6240, known to be a luminous merger in its late stages. Its
double nuclei, separated by a modest two thousand light-years,
has already been seen at wavelengths from the X-ray to the
radio. The astronomers used one of the spectral lines from the
abundant molecule carbon monoxide to probe the inner region of
the galaxy. The line also revealed the presence of gas motions
of up to two thousand kilometers per second, consistent with a
powerful wind driving a massive flow of material out of the

The new images were able to identify for the first time several
regions of outflow activity located only a few thousand
light-years from the and aligned as though they were
driven by processes associated with the nuclear black holes.
Moreover, these regions are spatially coincident with other
indicators of general activity like shocked gas and X-rays. The
new results are one of the first demonstrations that the widely
seen molecular outflow activity does originate from black hole
feedback mechanisms.

Explore further:

Co-evolution black hole mystery deepened by a new ALMA

More information: T Saito et al. Imaging the molecular
outflows of the prototypical ULIRG NGC 6240 with ALMA,
Monthly Notices of the Royal Astronomical Society:
(2017). DOI:

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