Spatially resolved Kennicutt-Schmidt relation at z ≈ 7 and its connection with the interstellar medium properties

Abstract

We exploit moderately resolved [O $\scriptstyle \rm III$], [C $\scriptstyle \rm II$] and dust continuum ALMA observations to derive the gas density (n), the gas-phase metallicity (Z), and the deviation from the Kennicutt-Schmidt (KS) relation (κ_s) on $\approx \, \rm sub-kpc$ scales in the interstellar medium (ISM) of five bright Lyman Break Galaxies at the Epoch of Reionization (z ≈ 7). To do so, we use GLAM, a state-of-art, physically motivated Bayesian model that links the [C $\scriptstyle \rm II$]and [O $\scriptstyle \rm III$]surface brightness (Σ_[CII], Σ_[OIII]) and the SFR surface density (Σ_SFR) to n, κ_s, and Z. All five sources are characterized by a central starbursting region, where the Σ_gas versus Σ_SFR align ≈10 × above the KS relation (κ_s ≈ 10). This translates into gas depletion times in the range t_dep ≈ 80 - 250 Myr. The inner starbursting centres are characterized by higher gas density (log (n/cm^-3) ≈ 2.5-3.0) and higher metallicity (log (Z/Z_⊙) ≈ -0.5) than the galaxy outskirts. We derive marginally negative radial metallicity gradients (∇log Z ≈ -0.03 ± 0.07 dex/kpc), and a dust temperature (T_d ≈ 32 - 38 K) that anticorrelates with the gas depletion time.