Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Siwei Zou, Zheng Cai, Feige Wang, Xiaohui Fan, Jaclyn B. Champagne
| Summary:
We characterize the multiphase circumgalactic medium and galaxy properties at
z = 6.0-6.5 in four quasar fields from the James Webb Space Telescope A
SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program.
We use the Very Large Telescope/X-shooter spectra of quasar J0305-3150 to
identify one new metal absorber at z = 6.2713 with multiple transitions (OI,
MgI, FeII and CII). They are combined with the published absorbing systems in
Davies et al. (2023a) at the same redshift range to form of a sample of nine
metal absorbers at z = 6.03 to 6.49. We identify eight galaxies within 1000 km
s$^{-1}$ and 350 kpc around the absorbing gas from the ASPIRE spectroscopic
data, with their redshifts secured by [OIII]($lambdalambda$4959, 5007)
doublets and H$beta$ emission lines. Our spectral energy distribution fitting
indicates that the absorbing galaxies have stellar mass ranging from 10$^{7.2}$
to 10$^{8.8}M_{odot}$ and metallicity between 0.02 and 0.4 solar. Notably, the
z = 6.2713 system in the J0305-3150 field resides in a galaxy overdensity
region, which contains two (tentatively) merging galaxies within 350 kpc and
seven galaxies within 1 Mpc. We measure the relative abundances of $alpha$
elements to iron ([$alpha$/Fe]) and find that the CGM gas in the most
overdense region exhibits a lower [$alpha$/Fe] ratio. Our modeling of the
galaxy’s chemical abundance favors a top-heavy stellar initial mass function,
and hints that we may be witnessing the contribution of the first generation
Population III stars to the CGM at the end of reionization epoch.
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