Probing the initial mass function of the first stars with transients

Abstract

The emergence of the first, so-called Population III (Pop III), stars shaped early cosmic history in ways that crucially depends on their initial mass function (IMF). However, because of the absence of direct observational constraints, the detailed IMF remains elusive. Nevertheless, numerical simulations agree in broad terms that the first stars were typically massive and should often end their lives in violent, explosive deaths. These fates include extremely luminous pair-instability supernovae (PISNe) and bright gamma-ray bursts (GRBs), the latter arising from the collapse of rapidly rotating progenitor stars into black holes. These high-redshift transients are expected to be within the detection limits of upcoming space telescope missions, allowing to place effective constraints on the shape of the primordial IMF that is not easily accessible with other probes. This paper presents a framework to probe the Pop III IMF, utilizing the cosmological source densities of high-redshift PISNe and GRBs. Considering these transients separately could provide useful constraints on the Pop III IMF, but tighter bounds are obtainable by combining PISN and GRB counts. This combined diagnostic is more robust as it is independent of the underlying Pop III star formation rate density, an unknown prior. Future surveys promise to capture most high-redshift GRBs across the entire sky, but high-redshift PISN searches with future telescopes, e.g. Roman Space Telescope, will likely be substantially incomplete. Nevertheless, we demonstrate that even such lower bounds on the PISN count will be able to provide key constraints on the primordial IMF, in particular, if it is top-heavy or not.

Euclid: Discovering pair-instability supernovae with the Deep Survey

“…If the PISN rate is sufficiently high, it is also possible that the Euclid mission will lead to the discovery of many PISNe with which PISNe in different environments and cosmic time can be studied. Identification and characterization of PISNe at z 3.5 by the Euclid mission will be an important base to discover and characterize PISNe at higher redshifts (z 3.5) which can be reached by future missions such as the Nancy Grace Roman Space Telescope (e.g., Moriya et al 2022;Lazar & Bromm 2021).…”

Probing Population III IMFs with He II/H$α$ Intensity Mapping

“…Additional information from the aforementioned observational probes and others such as, e.g., Galactic archaeology, direct/indirect observations of high-redshift transient events such as long gamma-ray bursts, pairinstability supernovae, and direct collapse black holes (Bromm 2013;Visbal et al 2015;Mebane et al 2018;Lazar & Bromm 2021) will be highly valuable to reduce the degeneracies mentioned here and to shed light on the IMF of Pop III stars.…”