GA-NIFS view of LAP1: Assembly of Pop~III stellar clusters during EoR

Abstract

Lensed and Pristine 1 (LAP1) is one of the most promising candidates for the detection of so-called Pop~III stars at $z\sim 6.6$. In this work, we present new high-spectral-resolution ($R\sim 2700$) \jwst NIRSpec-IFS observations of the system along with a detailed re-analysis of all archival \jwst and VLT/MUSE data. We confirm the very low metallicity of the system, with $12+\log (\text{O/H})=6.5\text{–}6.8$ (1--2\% Z${}_{\odot }$), and its low stellar mass, with $M_{\ast }=10^{3\text{–}4}$ \Msun, based on the non-detection in \jwst/NIRCam filter stacks and the \Hbeta luminosity. The high-resolution IFS data allow us to constrain the upper limits on the dynamical masses (${\log }_{10}(M_{\ast }/M_{\odot })$) of the A and B components to $<6.6\text{–}7.6$ and $<5.6\text{–}6.6$, respectively. Based on the metallicity and the high equivalent width of \Halpha (EW $>1200$\,Å), we estimate the possible range of the LAP1 stellar population ages to be $2\text{–}5$~Myr, consistent with the first burst of star formation in a pristine environment. Based on the size ($<10$~pc) and mass of the system, we discuss the nature of LAP1 as representing the formation of the first stellar clusters in a larger undetected galaxy, similar to other low-metallicity Pop~III candidates in the literature.

Submitted to MNRAS; 15 pages