Disentangling the source of the outflow as
either star formation or the AGN is difficult.
There are no obvious morphological differences between the two. Energy-scaling
arguments alone are insufficient, since the
underlying power — luminosity from star
formation, AGN, and related radio sources
— is generally correlated. A mix of all sources may be important. Nonetheless, these
results are broadly consistent with theoretical models of AGN-driven outflows that contribute to galactic feedback.
The complete results, including detailed
analysis of the individual galaxies observed,
are published in Monthly Notices of the Royal
Astronomical Society, 441: 3306, 2014, and a
preprint is available.
Figure 9.
An example object from
the GMOS observations.
The background image
is from the Sloan Digital
Sky Survey. The cyan
rectangle shows the
GMOS IFU field-of-view.
The red/yellow contours
show the distribution
of high-velocity ionized
gas. The inset shows
an example oxygen
emission-line profile ([O
III] 5007) that was used
to trace the gas velocity.
about the frequency, properties, and impact
of galaxy-wide energetic outflows.
The targets are relatively high luminosity,
with active galactic nucleus (AGN) contributions LAGN ~ 1045 erg/sec. They also exhibit
spectrally broad [O III] emission, but this is
not unusual, being characteristic of nearly
half the parent sample, even without correcting for the difficulty of measuring weak
broad components.
The team obtained data using the GMOSSouth Integral Field Unit (IFU), which enables spatially resolved kinematic measurements based on emission of Hb and [O III].
Bulk outflow velocities are typically in the
range of 500 to 1000 km/sec, and the emission-line profiles of the two species are generally similar.
The researchers find that the ionized oxygen
emission extends over sizes of 10-20 kiloparsecs, or even beyond the observed field-ofview (Figure 9). Mass and energy are flowing,
with mass outflow rates typically 10 times
the star-formation rate, though it is not certain whether this material will permanently
escape to the galaxy halo.
30
GeminiFocus
Studying High-redshift Star
Formation Nearby
Star-forming clumps are characteristic of
high-redshift galaxies, especially around the
peak epoch of star formation at z ~ 2. However, the endpoint of these massive clumps
of dense gas is uncertain; they could evolve
to provide the galaxy’s thick disk and bulge,
or they could be disrupted in place.
More sensitive observations and detailed
analysis are possible in the examination of
nearby galaxies; the challenge is to identify
appropriate analogs in the nearby universe
where these phenomena are uncommon.
Robert Bassett (Swinburne University of
Technology) and colleagues present two
examples of these rare, more local, analogs,
ultimately favoring the first scenario and
predicting that the clumps will supply the
hosts’ thick disks, rather than dissipate. The
studied z ~ 0.1 galaxies were selected from
among a larger sample identified by large
Hα luminosity, which then further showed
smooth rotation of their disks. These cases
are additionally similar to the high-z ex-
2014 Year in Review
January 2015