Transient star B/R ratio and star formation in $z\gtrsim 1$ lensed galaxies

Abstract

The extreme magnification from galaxy clusters and microlenses therein allows the detection of individual, luminous stars in lensed galaxies as transient events, and hence provides a valuable window into the high mass stellar population in $z>1$ galaxies. As these bright stars can only be formed at specific ages, the relative abundance of transient events at blue (B) and red (R) optical wavelengths ($B/R$ ratio) can provide insights into the recent star formation history of galaxies that are not well constrained by their spectral energy distributions (SEDs). Here, we forward model the transient detection rates in an idealized mock scenario to find that the $B/R$ ratio of strongly lensed $z>1$ galaxies decreases quickly with increasing age. This ratio has moderate sensitivity to metallicity and comparatively low sensitivity to dust attenuation, with no significant dependency on the stellar initial mass function. Fitting model stellar populations to either the SED or $B/R$ ratio alone of ``Warhol'' arc ($z=0.94$), we find that neither a simple single starburst nor a more complex star formation can simultaneously reproduce both constraints. We then demonstrate that a best-fit model constrained by both the B/R ratio and SED requires a star-formation rate that has varied quite dramatically over the past $\sim$50 Myr, for which the total stellar mass formed over this time is a factor of 10 (with $2-3\sigma$ significance) different from the best-fit models to the SED alone. Our work shows that the transient $B/R$ ratio can be used as an additional powerful constraint on the recent star formation history of higher-redshift galaxies in future works that are strongly lensed by galaxy clusters.

12 pages, 14 figures, accepted for publication in Astronomy & Astrophysics

References in corpus (16)

• Understanding caustic crossings in giant arcs: characteristic scales, event rates, and constraints on compact dark matter
• COSMOS2020: The Galaxy Stellar Mass Function: the assembly and star formation cessation of galaxies at $0.2<z\le 7.5$
• JWST's PEARLS: Prime Extragalactic Areas for Reionization and Lensing Science: Project Overview and First Results
• A Highly Magnified Star at Redshift 6.2
• The time-scales probed by star formation rate indicators for realistic, bursty star formation histories from the FIRE simulations
• Galaxy Build-up in the first 1.5 Gyr of Cosmic History: Insights from the Stellar Mass Function at $z\sim 4-9$ from JWST NIRCam Observations
• Einstein rings modulated by wavelike dark matter from anomalies in gravitationally lensed images
• JWST's PEARLS: a new lens model for ACT-CL J0102$-$4915, "EL Gordo'', and the first red supergiant star at cosmological distances discovered by JWST
• SPISEA: A Python-Based Simple Stellar Population Synthesis Code for Star Clusters
• Outshining in the Spatially Resolved Analysis of a Strongly-Lensed Galaxy at z=6.072 with JWST NIRCam
• JWST's PEARLS: 119 multiply imaged galaxies behind MACS0416, lensing properties of caustic crossing galaxies, and the relation between halo mass and number of globular clusters at $z=0.4$
• Statistics of magnification for extremely lensed high redshift stars
• Imaging dark matter at the smallest scales with $z\approx 1$ lensed stars
• Flashlights: An Off-Caustic Lensed Star at Redshift $z$ = 1.26 in Abell 370
• Are Models of Strong Gravitational Lensing by Clusters Converging or Diverging?
• Microlensing at Cosmological Distances: Event Rate Predictions in the Warhol Arc of MACS 0416

Cited by in corpus (1)

• Kinematic Mapping of Giant Arcs: A New Method to Locate Lensing Critical Curves