imaging with HST clearly resolved the sys-
tem into multiple lensed components with
a maximum separation of about 0.2 arc-
second, plus an extended source about 0.5
arcsecond away, interpreted as the lensing
galaxy. Photometric analysis implied a red-
shift of about 0.7 and a mass of 6.3 billion
solar masses for the lensing galaxy. Based
on these measurements, the team derived a
best-fit lensing model with three quasar im-
ages and a total magnification factor of 51.3.
After correcting for the magnification, the
inferred luminosity of J0439+1634 drops to
“only” 1.1 × 10 13 solar luminosities, and its
black hole‘s mass becomes a pedestrian 430
million solar masses. Together these esti-
mates imply an extremely high mass accre-
tion rate, as required to grow such a large
black hole at early times.
The results of this study indicate that many
strongly lensed, high-redshift quasars could
have been missed by past surveys because
standard color selection criteria will fail
when the quasar light is contaminated by
a lensing galaxy. Thus, changing the tech-
niques for selecting quasars could signifi-
cantly increase the number of lensed quasar
discoveries. “This discovery demonstrates
that strongly gravitationally lensed quasars
do exist at redshift above five, despite the
fact that we’ve been looking for over 20
years and have not found any others this far
back in time,” said Fan. “However, we don’t
expect to find many quasars brighter than
this one in the whole observable Universe.”
The study has been published in The Astro-
physical Journal Letters.
Excavation of an Ancient Star
Cluster Deep in Milky Way Bulge
Of the roughly 160 globular clusters known
in the Milky Way, roughly a quarter appear
to be associated with the Galactic bulge. Al-
though these are generally more metal rich
April 2019
than those of the halo, a subclass of moder-
ately metal-poor ([Fe/H] < −1.0), α-enhanced
([α/Fe] > + 0.3), bulge globular clusters with
blue horizontal branches are thought to be
among the oldest stellar systems in the Gal-
axy. In this scenario, the moderate metallici-
ties of these ancient star clusters result from
the early, rapid chemical enrichment of the
Milky Way’s innermost regions.
One such candidate “fossil relic” of the
bulge’s early formation is HP 1, a globular
cluster just 3° away from the Galactic Cen-
ter with 3.7 magnitudes of visual extinction.
High-dispersion spectroscopy of member
red giants indicates that HP 1 has metallic-
ity [Fe/H] ≈ − 1.1 dex and is α-enhanced by
about a factor of two. However, the age had
been uncertain because past photometric
studies were unable to reach beyond the
main sequence turn-off (MSTO).
Figure 4.
The Gemini GeMS+GSAOI
J, K color composite image
of HP 1 (right) is shown
within the context of a
larger field imaged under
natural seeing conditions
by the Visible and Infra-
red Survey Telescope for
Astronomy (VISTA, left).
Note: the background of
the right-hand image is
featured on the cover of
this issue of GeminiFocus.
A new study by an international team of as-
tronomers presents a detailed analysis of
deep near-infrared observations of HP 1 ob-
tained with the Gemini South Adaptive Op-
tics Imager (GSAOI) using the Gemini Multi-
conjugate adaptive optics System (GeMS).
The GeMS/GSAOI J and K s images, shown in
Figure 4 (also featured on the cover of this
issue), have spatial resolution of about 0.1
arcsecond and probe two magnitudes be-
GeminiFocus
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