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.
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
38
GeminiFocus
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-
est work in the MASSIVE series presents the
first results from the high angular resolution
portion of the survey, based on deep GMOS-
North IFS observations of 20 galaxies. These
are combined with wide-field IFS data from
the Mitchell spectrograph at McDonald Ob-
servatory to obtain detailed kinematic maps
spanning more than two orders of magni-
tude in galactocentric radius. The new study
appears in the June issue of The Astrophysical
Journal and is led by graduate student Irina
Ene of the University of California, Berkeley.
Figure 13 (next page) shows example maps
of the first four moments (v, σ, h 3 , and h 4 ) of
the stellar velocity distributions from the
high-quality GMOS IFS data for two galax-
ies in the survey. The maps cover the cen-
tral 5 × 7 arcseconds. The figure also shows
the one-dimensional distributions of these
parameters combined with the wider field
IFS measurements. Although both galaxies
exhibit strong central rotation, they have
strikingly different kinematic profiles. In fact,
most of the galaxies in the MASSIVE sample
show only slow rotation (unlike most previ-
ous IFS studies of early-type galaxies, which
were weighted towards lower luminosity).
Interestingly, in galaxies that do rotate, the
central rotation is often unaligned with the
large-scale kinematics, indicating diverse
merger histories.
January 2020 / 2019 Year in Review