A number of absorption lines were
used to determine the host galaxy’s
redshift. Some of these lines are useful tracers of the galaxy’s metallicity,
with the expected result of low metallicity — about one-tenth of solar
values. Assuming these lines are optically thin, it sets a lower limit; e.g.,
[Si/H] -1.7. The non-detection of
some ionized sulfur lines sets an upper limit of [S/H] - 0.5.
The complete results are published
in The Astrophysical Journal, 774: 26,
2013.
First Refereed GeMS Results:
Young Stars Leave the Nest
Figure 5.
This artistic rendering
illustrates how the light
from GRB 130606A
serves as a beacon
through the interstellar
gas of the host galaxy of
the burst source. It also
reveals the ionization
state of the medium
between galaxies along
the line-of-sight.
reionization in the early universe and properties of the host galaxy (Figure 5).
At redshift z = 5.91, GRB 130606A remains
one of just a handful of spectroscopically
confirmed GRBs at z 6. Quasars have been
used to probe the intergalactic medium
(IGM) at this epoch, when the universe was
only one billion years old. This work is the
first to provide a similarly high-quality GRB
spectrum for analysis.
The first refereed astronomy paper based on data using the Gemini Multiconjugate adaptive optics System (GeMS)
demonstrates the effective use of young,
lower-mass stars to determine the age of a
star cluster. In this case, the infrared sensitivity and resolution of GeMS, together with the
Gemini South Adapative Optics Imager (GSAOI), enabled measurements of stars in the
low-mass cluster Haffner 16 in the Milky Way.
An advantage of pursuing this work with
GRBs is that there is no expected bias toward highly ionized areas, as may be the
case with quasars. The net results along this
single sightline are similar to those obtained
based on quasar observations, showing an
increase in the Lyman-α optical depth from
z = 4.9 toward larger redshifts.
A particular feature is that the IGM appears
nearly opaque in a region around z = 5.77,
although measurable Lyman-β and Lyman-γ
flux show that the IGM is still significantly
ionized over this high-redshift interval. In
addition, at the redshift of the host galaxy,
Chornock et al. establish an upper limit on
the neutral fraction of the IGM of 0.11.
30
In particular, photometry of faint, pre-mainsequence stars is now possible. These become essential for determining the cluster’s
age accurately because the higher-mass
stars usually used are often absent in lowmass clusters. The GeMs/GSAOI data yield
an age 10 million years (Myr). In contrast,
optical measurements result in an age about
2 Myr greater for this cluster.
One of the broader interests of lead author Tim Davidge (Dominion Astrophysical
Observatory, Canada) is the origin of the
field-star population — stars that have “left
the nest” of the clusters where they likely
formed. Haffner 16 is an example of a cluster in the processes of dissolving, providing
GeminiFocus 2013 Year in Review
January2014