Microlensing at cosmological distances: Event rate predictions in the Warhol arc of MACS 0416

¹ Instituto de Física de Cantabria (CSIC-UC), Avda. Los Castros s/n, 39005 Santander, Spain
² Department of Physics, University of California, 366 Physics North MC 7300, Berkeley, CA 94720, USA
³ Department of Astronomy, University of California, 501 Campbell Hall #3411, Berkeley, CA 94720, USA
⁴ School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA
⁵ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
⁶ Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong
⁷ Center for Astrophysics Harvard & Smithsonian: Cambridge, Massachusetts, US
⁸ Department of Physics, Ben-Gurion University of the Negev, PO Box 653, Be’er-Sheva 8410501, Israel
⁹ Department of Theoretical Physics, University of Basque Country UPV/EHU, Bilbao, Spain
¹⁰ Ikerbasque, Basque Foundation for Science, Bilbao, Spain
¹¹ Donostia International Physics Center, Paseo Manuel de Lardizabal, 4, San Sebastián, 20018, Spain
¹² Minnesota Institute for Astrophysics, University of Minnesota, 116 Church St. SE, Minneapolis, MN 55455, USA

^⋆ Corresponding author: palencia@ifca.unican.es

Received: 8 May 2025
Accepted: 9 June 2025

Abstract

Highly magnified stars (μ>100) are now routinely identified as transient events at cosmological distances thanks to microlensing by intra-cluster stars near the critical curves of galaxy clusters. Using the James Webb Space Telescope (JWST) in combination with the Hubble Space Telescope, we outline here an analytical framework that is applied to the Warhol arc (at z = 0.94) in the MACS 0416 galaxy cluster (at z = 0.396), where over a dozen microlensed stars have been detected to date. This method is general and can be applied to other lensed arcs. Within this lensed galaxy, we fit the spatially resolved spectral energy distribution spanned by eight JWST-NIRCam filters combined with three ACS filters, for accurate lensed star predictions in 2D. With this tool we can generate 2D maps of microlensed stars for well-resolved arcs in general, incorporating wavelength dependence and limiting apparent magnitude. These maps can be directly compared with planned cadenced campaigns from JWST and Hubble, offering a means to constrain the initial mass function and the level of dark matter substructure.