Microlensing at Cosmological Distances: Event Rate Predictions in the Warhol Arc of MACS 0416

Abstract

Highly magnified stars ($\mu$ $>$ 100) are now outinely identified as transient events at cosmological distances thanks to microlensing by intra-cluster stars near the critical curves of galaxy clusters. Using the {\it James Webb} Space Telescope (JWST) in combination with the {\it Hubble} Space Telescope (HST), 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 SED 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, including dependence on wavelength and limiting apparent magnitude, for comparison with with planned cadenced campaigns for JWST and Hubble, for constraining directly the IMF and the level of dark matter substructure.

19 pages, 13 figures

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• Flashlights: Prospects for constraining the Initial Mass Function around cosmic noon with caustic-crossing events
• Transient star B/R ratio and star formation in $z\gtrsim 1$ lensed galaxies
• Kinematic Mapping of Giant Arcs: A New Method to Locate Lensing Critical Curves
• Lensed stars in galaxy-galaxy strong lensing -- a JWST prediction for the Cosmic Horseshoe