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

Abstract

We exploit moderately resolved [OIII], [CII] 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 (${\kappa }_s$) on ~sub-kpc scales in the interstellar medium (ISM) of five bright Lyman Break Galaxies at the Epoch of Reionization ($z\approx 7$). To do so, we use GLAM, a state-of-art, physically motivated Bayesian model that links the [CII] and [OIII] surface brightness (${\Sigma }_{[\mathrm{CII}]}$, ${\Sigma }_{[\mathrm{OIII}]}$) and the SFR surface density (${\Sigma }_{\mathrm{SFR}}$) to $n$, ${\kappa }_s$, and $Z$. All five sources are characterized by a central starbursting region, where the ${\Sigma }_{\mathrm{gas}}$ vs ${\Sigma }_{\mathrm{SFR}}$ align ~10x above the KS relation (${\kappa }_s\approx 10$). This translates into gas depletion times in the range $t_{\mathrm{dep}}\approx 80-250$ Myr. The inner starbursting centers are characterized by higher gas density ($\log (n/\mathrm{c}{\mathrm{m}}^{-3})\approx 2.5-3.0$) and higher metallicity ($\log (Z/Z_{\odot })\approx -0.5$) than the galaxy outskirts. We derive marginally negative radial metallicity gradients ($\nabla \log Z\approx -0.03\pm 0.07$dex/kpc), and a dust temperature ($T_d\approx$32-38 K) that anticorrelates with the gas depletion time.

13 pages, 7 figures. Resubmitted to MNRAS after addressing the referee comments