Accounting for the detection
sensitivity curves and com-
bining their results with those
from radial velocity studies
(sensitive to companions at
smaller radii), the team con-
cluded that the most likely
location for giant planets to
occur is between 1 and 10 au
from their host stars. The oc-
currence rate drops steeply at
larger separations. The number
of giant planets also declines
significantly with increasing planetary mass.
Although brown dwarfs are often consid-
ered transitional objects between planets
and stars, they appear to have quite different
demographics than giant planets, as shown
in Figure 3. The study concludes that only
about one in ten stars hosts a brown dwarf
companion at separations of 10 to 100 au.
This is a factor of ten below the inferred oc-
currence rate of giant planets around high-
mass stars. Moreover, although the numbers
are low, the distributions in both mass and
semi-major axis are consistent with being
flat for brown dwarfs, in contrast with the
falling distributions for giant planets. In ad-
dition, the detected brown dwarfs all orbit
stars with masses below 1.5 M B , again unlike
the giant planets.
Based on these results, earlier suggestions
that wide-separation giant planets and
brown dwarfs may comprise a single under-
lying population is unlikely to be correct.
The divergent trends strongly indicate dis-
parate formation mechanisms. Specifically,
the study concludes that giant planets likely
form “bottom up” through the process of
core accretion while brown dwarfs form “top
down” like stars via gravitational instabil-
ity. More data are needed to confirm these
trends; fortunately, there are another 231
stars from the rest of the GPIES survey await-
ing final analysis and publication.
July 2019
Spatially Resolved Kinematics
of 20 MASSIVE Ellipticals
Every galaxy has its own story, and every gal-
axy has been many others in the past (un-
like in the human parallel, this is not purely
metaphorical, as galaxies grow via hierarchi-
cal assembly). Generally speaking, the most
massive galaxies have led the most interest-
ing lives. These often reside in dense envi-
rons that have exposed them to frequent
interactions with assorted neighbors, influ-
encing in complex ways the coevolution of
their component stars, gas, dark matter, and
supermassive black holes.
Although the detailed formation histories of
most galaxies will remain forever uncertain,
the key thematic elements may be surmised
through a variety of methods. A particularly
powerful probe of a galaxy’s dynamical struc-
ture is integral field spectroscopy (IFS). Wide-
field IFS studies provide insight into global
dynamics and past interactions, while IFS
data on the innermost regions can constrain
the central supermassive black hole (SMBH)
mass and the shapes of the stellar orbits in
the vicinity of its sphere of influence.
The MASSIVE Galaxy Survey is systemati-
cally targeting all early-type galaxies in the
northern hemisphere with stellar masses
greater than 3 × 10 11 M B within a distance
of about 100 megaparsecs for detailed ki-
nematic and photometric analysis. The lat-
GeminiFocus
Figure 3.
GPIES sensitivity contours
for companion mass (in
units of Jupiter masses)
and orbital semi-major
axis (astronomical units)
for planetary (left) and
brown dwarf (right) com-
panions. The six giant
planets and three brown
dwarfs detected in the
survey are overlaid on
the contours. Although
the majority of these
companions were not
discovered by GPIES,
their host stars were part
of the unbiased sample
and were not selected
because of the pres-
ence of the companions;
thus, the detections are
included in the statistical
analysis. The curves indi-
cate the numbers of stars
in the sample for which
the sensitivity allowed
detection of compan-
ions with the plotted
combinations of param-
eters; very few stars had
sensitivity sufficient to
detect planets of masses
< 3 M Jup , but two were
detected.
[Figure reproduced from
Nielsen et al., The Astro-
nomical Journal, 158:
13, 2019.]
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