Kavli Affiliate: Alexander P. Ji
| First 5 Authors: Anya E. Nugent, Alexander P. Ji, Wen-fai Fong, Hilay Shah, Freeke van de Voort
| Summary:
Neutron star (NS) mergers are currently the only observed source of r-process
production in the Universe. Yet, it is unclear how much r-process mass from
these mergers is incorporated into star-forming gas to enrich stars. This is
crucial to consider as all other r-process mass estimates in the Universe
beyond Earth are based on stellar r-process abundances. Here, we explore the
extent to which merger location and host galaxy properties affect the
incorporation of r-process elements into star-forming gas, and quantify an
“enrichment" timescale to account for this process. To put this timescale in
context, we analyze a population of 12 gamma-ray bursts (GRBs) with probable
associations to r-process kilonovae (GRB-KNe) and 74 short GRBs without claimed
KNe, including new non-parametric star formation histories for the GRB-KN
hosts. We find enrichment timescales for this sample are between ~7 Myr-1.6
Gyr, suggesting that environmental enrichment is delayed from NS merger
occurrence. Moreover, we find a correlation between the amount of environmental
enrichment from a single event and increasing host specific star formation rate
(sSFR), and little correlation with stellar mass and GRB galactocentric offset.
Environments with low sSFRs (<10^-10.5 yr^-1), which comprise 18% of short GRB
hosts and the host of GW170817, will have little to no capacity for enrichment.
Our results indicate that not all r-process from NS mergers enriches
star-forming gas, and instead some is lost to the CGM or IGM. Future studies
should consider these losses to understand the total contribution from NS
mergers to the Universe’s r-process budget.
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