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

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

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


Jose M. Diego

Sung Kei Li

Ashish K. Meena

Anna Niemiec

Ana Acebron

Mitchell F. Struble

Alfred Amruth

Tom J. Broadhurst

Harald Ebeling

Alexei V. Filippenko

Eric Jullo

Patrick Kelly

Anton M. Koekemoer

Jeremy Lim

Marceau Limousin

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Nency Patel
PGR Student Doctor of Philosophy

Juan Remolina

Johan Richard

Keren Sharon

Charles Steinhardt

Keiichi Umetsu

Liliya Williams

Adi Zitrin

Jose María Palencia

Liang Dai

Lingyuan Ji

Massimo Pascale


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.


Diego, J. M., Li, S. K., Meena, A. K., Niemiec, A., Acebron, A., Jauzac, M., …Pascale, M. (2024). BUFFALO/Flashlights: Constraints on the abundance of lensed supergiant stars in the Spock galaxy at redshift 1. Astronomy & Astrophysics, 681, Article A124.

Journal Article Type Article
Acceptance Date Nov 1, 2023
Online Publication Date Jan 24, 2024
Publication Date 2024-01
Deposit Date Mar 26, 2024
Publicly Available Date Mar 26, 2024
Journal Astronomy & Astrophysics
Print ISSN 0004-6361
Electronic ISSN 1432-0746
Publisher EDP Sciences
Peer Reviewed Peer Reviewed
Volume 681
Article Number A124
Keywords Space and Planetary Science; Astronomy and Astrophysics
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Copyright Statement
© The Authors 2024
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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