images. Higher resolution imaging with HST
clearly resolved the system into multiple
lensed components with a maximum sepa-
ration of about 0.2 arcsecond, plus an ex-
tended source about 0.5 arcsecond away, in-
terpreted as the lensing galaxy. Photometric
analysis implied a redshift of about 0.7 and a
mass of 6.3 billion solar masses for the lens-
ing galaxy. Based on these measurements,
the team derived a best-fit lensing model
with three quasar images and a total mag-
nification 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 be-
comes a pedestrian 430 million solar masses.
Together these estimates imply an extremely
high mass accretion 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
January 2020 / 2019 Year in Review
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.
Figure 18.
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).
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).
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 18, have spatial resolution of about 0.1
arcsecond and probe two magnitudes be-
low the MSTO. The study was led by Leandro
GeminiFocus
43