Long GRBs as a tool to investigate star formation in dark matter halos

Abstract

First stars can only form in structures that are suitably dense, which can be parametrized by the minimum dark matter halo mass Mmin. Mmin must play an important role in star formation. The connection of long gamma-ray bursts (LGRBs) with the collapse of massive stars has provided a good opportunity for probing star formation in dark matter halos. We place some constraints on Mmin using the latest Swift LGRB data. We conservatively consider that LGRB rate is proportional to the cosmic star formation rate (CSFR) and an additional evolution parametrized as (1+z)α, where the CSFR model is a function of Mmin. Using the χ2 statistic, the contour constraints on the Mmin–α plane show that at the 1σ confidence level, we have Mmin<1010.5M⊙ from 118 LGRBs with redshift z<4 and luminosity Liso>1.8×1051 ergs−1. We also find that adding 12 high-z(4<z<5) LGRBs (consisting of 104 LGRBs with z<5 and Liso>3.1×1051 ergs−1) could result in much tighter constraints on Mmin, for which, 107.7M⊙<Mmin<1011.6M⊙ (1σ). Through Monte Carlo simulations, we estimate that future five years of Sino–French spacebased multiband astronomical variable objects monitor (SVOM) observations would tighten these constraints to 109.7M⊙<Mmin<1011.3M⊙. The strong constraints on Mmin indicate that LGRBs are a new promising tool for investigating star formation in dark matter halos.