Nancy A. Levenson and Mischa Schirmer
Science Highlights
Recent significant scientific results based on Gemini data include
determining the physical characteristics of a massive galaxy
consisting almost entirely of dark matter, confirming the existence
of several nearby Earth-sized exoplanets around a cool dwarf star,
and obtaining the first-ever close-up images of Lyman-alpha blobs
at low redshifts.
A Dark Matter Milky Way
Astronomers have discovered a massive galaxy that is almost entirely dark matter. The galaxy,
called Dragonfly 44, has very low surface brightness and was discovered only in 2014. New
Fast Turnaround program observations using the Gemini Multi-Object Spectrograph (GMOS)
on Gemini North, as well as spectroscopy
from the Keck II telescope also on Maunakea,
reveal the galaxy’s physical properties. They
show that it is like a “failed” Milky Way, in having similar total mass, size, and population of
globular clusters, lacking only stars.
Figure 1.
The dark galaxy
Dragonfly 44,
observed using GMOSNorth, in wide- field
(left) and close-up
(right). Dragonfly 44 is
very faint for its mass,
and consists almost
entirely of dark matter.
Credit: P. van Dokkum
et al., Gemini
Observatory/AURA
The Keck spectroscopy enabled Pieter van
Dokkum (Yale University) and collaborators to
measure the mass of Dragonfly 44. The deep
images from Gemini (featured on the cover
of this issue and in Figure 1) then yielded the
galaxy’s mass-to-light ratio (48 within the
half-light radius), and the Gemini imaging
shows the large population of globular clusters in the halo. Considering theoretical models that include the halo, the researchers con-
October 2016
GeminiFocus
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