Modelling the chemical enrichment of Population III supernovae: The origin of the metals in near-pristine gas clouds.

Abstract

The most metal-poor, high redshift damped Lyman α systems (DLAs) provide a window to study some of the first few generations of stars. In this paper, we present a novel model to investigate the chemical enrichment of the near-pristine DLA population. This model accounts for the mass distribution of the enriching stellar population, the typical explosion energy of their supernovae, and the average number of stars that contribute to the enrichment of these DLAs. We conduct a maximum likelihood analysis of these model parameters using the observed relative element abundances ([C/O], [Si/O], and [Fe/O]) of the 11 most metal-poor DLAs currently known. We find that the mass distribution of the stars that have enriched this sample of metal-poor DLAs can be well-described by a Salpeter-like IMF slope at M > 10 M and that a typical metal-poor DLA has been enriched by 72 massive stars (95 per cent confidence), with masses 40 M . The inferred typical explosion energy (Ê exp = 1.8 +0.3 −0.2 × 10 51 erg) is somewhat lower than that found by recent works that model the enrichment of metal-poor halo stars. These constraints suggest that some of the metal-poor DLAs in our sample may have been enriched by Population II stars. Using our enrichment model, we also infer some of the typical physical properties of the most metal-poor DLAs. We estimate that the total stellar mass content is log 10 (M /M ) = 3.5 +0.3 −0.4 and the total gas mass is log 10 (M gas / M ) = 7.0 +0.3 −0.4 for systems with a relative oxygen abundance [O/H] ≈ −3.0.

MUSE Analysis of Gas around Galaxies (MAGG) – I: Survey design and the environment of a near pristine gas cloud at z ≈ 3.5

“…Despite their small number, these systems are of considerable interest being possible candidates for clouds that may have been enriched solely by the very first generation of stars (e.g. Welsh et al 2019). These clouds could also be the antecedents of the lowest mass galaxies in the local Universe, and are compelling candidates of the elusive cold-mode accretion.…”

A limit on Planck-scale froth with ESPRESSO

“…The most metal-poor DLAs are clouds of gas that have been enriched by at most a few generations of stars (Welsh, Cooke & Fumagalli 2019), and in some cases, exhibit just a single absorption component of kinematically quiescent gas (see e.g. the line profiles of the systems reported by Pettini et al 2008;Cooke et al 2011a,b).…”

A bound on the 12C/13C ratio in near-pristine gas with ESPRESSO

“…ter modelled by Population III or Population II enrichment, we can exploit the stochastic chemical enrichment model developed by Welsh et al (2019), alongside the yields from simulations of stellar evolution. The resulting enrichment models can be used to infer the epoch at which this DLA formed its enriching stars as well as its total stellar mass and total gas mass.…”

“…In previous work (Welsh et al 2019), we developed a stochastic chemical enrichment model that uses the abundance patterns of near-pristine environments to infer their chemical enrichment history. This model describes the initial mass function (IMF) of an enriching stellar population as a power law, governed by the slope, α.…”

“…These distributions can then be used to gauge the likelihood of measuring our observed abundances given any underlying enrichment model. This approach assumes that the gas within the DLA is well-mixed and that the system experiences no inflow or outflow of gas; for further details of this model, see Welsh et al (2019). The stellar yields used in this analysis are from three sources: (1) Campbell & Lattanzio (2008), hereafter CL08, who simulate the evolution of low mass metal-free stars in the mass range (1 − 3) M ; (2) Karakas (2010) (> 10 M ) metal-free stars.…”