GeminiFocus April 2019 - Page 13

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 11