Speaker
Description
We present a proof-of-concept study using lensed stars as a pioneer probe of the high-mass stellar initial mass function (IMF) at z~1 galaxies. Residing at cosmological distances, only the most luminous stars can be detected as a transient event even with the extreme magnification under the strong lensing effect from galaxy clusters and the microlensing effect from foreground intra-cluster stars combined. These luminous stars are consequently the most massive stars, the abundance of which is highly sensitive to the IMF and the star formation history (SFH). Assuming simple SFH models constrained by photometric measurements, we predict the transient detection rate in a lensed galaxy known as ``Spock’’ (z = 1) under different IMFs. With a Salpeter IMF, we can well reproduce the transient detection rate featuring young blue stars, as observed by HST and JWST. We found that the abundance of these young stars is very sensitive to the IMF and the most recent star formation rate, independent of the SFH model assumed. Given our methodology and assumptions, our Bayesian analysis thus infers that the observed transient detection rate prefers the “Spock” galaxy to have a Salpeter IMF instead of a top-heavy IMF, which would otherwise have overpredicted the transient detection rate significantly. With the many upcoming JWST imaging surveys, our proposed methodology can make use of the anticipated increasing amount of transients detected to potentially constrain the high-mass IMF of lensed galaxies, or even the IMF evolution throughout cosmic history.
