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

¹ Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n, 39005 Santander, Spain
e-mail: jdiego@ifca.unican.es
² Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
³ Physics Department, Ben-Gurion University of the Negev, PO Box 653 Be’er-Sheva 84105, Israel
⁴ LPNHE, CNRS/IN2P3, Sorbonne Université, Université Paris-Cité, Laboratoire de Physique Nucléaire et de Hautes Énergies, 75005 Paris, France
⁵ Department of Physics of the University of Milano, via Celoria 16, 20133 Milano, Italy
⁶ INAF – IASF Milano, via A. Corti 12, 20133 Milano, Italy
⁷ Center for Extragalactic Astronomy, Durham University, South Rd, Durham DH1 3LE, UK
⁸ Institute for Computational Cosmology, Durham University, South Road, Durham DH1 3LE, UK
⁹ Astrophysics Research Center, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa
¹⁰ School of Mathematics, Statistics & Computer Science, University of KwaZulu-Natal, Westville Campus, Durban 4041, South Africa
¹¹ Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA
¹² Department of Physics, University of Hong Kong, Hong Kong, Hong Kong SAR
¹³ Department of Physics, University of the Basque Country UPV/EHU, 48080 Bilbao, Spain
¹⁴ DIPC, Basque Country UPV/EHU, 48080 San Sebastian, Spain
¹⁵ Ikerbasque, Basque Foundation for Science, 48011 Bilbao, Spain
¹⁶ Institute for Astronomy, University of Hawaii, 640 N Aohoku Pl, Hilo, HI 96720, USA
¹⁷ Department of Astronomy, University of California, Berkeley, CA 94720-3411, USA
¹⁸ Aix-Marseille Univ., CNRS, CNES, LAM, 13388 Marseille, France
¹⁹ Minnesota Institute for Astrophysics, University of Minnesota, 116 Church Street SE, Minneapolis, MN 55455, USA
²⁰ Space Telescope Science Institute, 3700 San Martin Dr., Baltimore, MD 21218, USA
²¹ Department of Astronomy, University of Michigan, 1085 S. University Ave, Ann Arbor, MI 48109, USA
²² Univ. Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
²³ Niels Bohr Institute, University of Copenhagen, Lyngbyvej 2, København Ø 2100, Denmark
²⁴ Institute of Astronomy and Astrophysics, Academia Sinica (ASIAA), AS/NTU Astronomy-Mathematics Building, No. 1, Sec. 4, Roosevelt Rd., Taipei 10617, Taiwan
²⁵ School of Physics and Astronomy, University of Minnesota, 116 Church Street, Minneapolis, MN 55455, USA
²⁶ Department of Physics, University of California, 366 Physics North MC 7300, Berkeley, CA 94720, USA

Received: 27 April 2023
Accepted: 1 November 2023

Abstract

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 Ultra-deep 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 (L_max ≈ 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.