BUFFALO/Flashlights: Constraints on the abundance of lensed supergiant stars in the Spock galaxy at redshift 1

Jose M. Diego, Sung Kei Li, Ashish K. Meena, Anna Niemiec, Ana Acebron, Mathilde Jauzac, Mitchell F. Struble, Alfred Amruth, Tom J. Broadhurst, Catherine Cerny, Harald Ebeling, Alexei V. Filippenko, Eric Jullo, Patrick Kelly, Anton M. Koekemoer, David Lagattuta, Jeremy Lim, Marceau Limousin, Guillaume Mahler, Nency PatelJuan Remolina, Johan Richard, Keren Sharon, Charles Steinhardt, Keiichi Umetsu, Liliya Williams, Adi Zitrin, Jose María Palencia, Liang Dai, Lingyuan Ji, Massimo Pascale

Research output: Contribution to journalArticlepeer-review


In this work, we present a constraint on the abundance of supergiant (SG) stars at redshift z ≈ 1, based on recent observations of a strongly lensed arc at this redshift. First we derived a free-form model of MACS J0416.1-2403 using data from the Beyond Ultradeep Frontier Fields and Legacy Observations (BUFFALO) program. The new lens model is based on 72 multiply lensed galaxies that produce 214 multiple images, making it the largest sample of spectroscopically confirmed lensed galaxies on this cluster. The larger coverage in BUFFALO allowed us to measure the shear up to the outskirts of the cluster, and extend the range of lensing constraints up to ∼1 Mpc from the central region, providing a mass estimate up to this radius. As an application, we make predictions for the number of high-redshift multiply lensed galaxies detected in future observations with the James Webb Space Telescope (JWST). Then we focus on a previously known lensed galaxy at z = 1:0054, nicknamed Spock, which contains four previously reported transients. We interpret these transients as microcaustic crossings of SG stars and explain how we computed the probability of such events. Based on simplifications regarding the stellar evolution, we find that microlensing (by stars in the intracluster medium) of SG stars at z = 1:0054 can fully explain these events. The inferred abundance of SG stars is consistent with either (1) a number density of stars with bolometric luminosities beyond the Humphreys-Davidson (HD) limit (Lmax ≈ 6 × 105 L⊙ for red stars), which is below ∼400 stars kpc-2, or (2) the absence of stars beyond the HD limit but with a SG number density of ∼9000 kpc-2 for stars with luminosities between 105 L⊙ and 6 × 105 L⊙. This is equivalent to one SG star per 10 × 10 pc2. Finally, we make predictions for future observations with JWST's NIRcam. We find that in observations made with the F200W filter that reach 29 mag AB, if cool red SG stars exist at z ≈ 1 beyond the HD limit, they should be easily detected in this arc.

Original languageEnglish
Article numberA124
JournalAstronomy and Astrophysics
StatePublished - 1 Jan 2024


  • Gravitation
  • Gravitational lensing: strong
  • Supergiants

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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