The NOEMA observations of GN-z11: constraining the neutral interstellar medium and dust formation in the heart of cosmic reionization at z = 10.6

Abstract

We present results of dust continuum and [C ii] 158 μm emission line observations of a remarkably UV-luminous (MUV = −21.6) galaxy at z = 10.603: GN-z11. Using the Northern Extended Millimeter Array (NOEMA), observations have been carried out over multiple observing cycles. We achieved a high sensitivity resulting in a λrest = 160 μm continuum 1 σ sensitivity of $13.0\, \rm {\mu Jy/beam}$ and a [C ii] emission line 1 σ sensitivity of $31\, \rm {mJy/beam\, km/s}$ using $50\, \rm {km/s}$ binning with a ∼2 arcsec synthesized beam. Neither dust continuum nor [C ii] 158 μm line emission are detected at the expected frequency of $\nu _{\rm [CII]} = 163.791\, \rm {GHz}$ and the sky location of GN-z11. The upper limits show that GN-z11 is neither luminous in LIR nor L[CII], with a dust mass 3 σ limit of ${\rm log}(M_{\rm dust}/{\rm {\rm M}_{\odot }}) < 6.5-6.9$ and with a [C ii] based molecular gas mass 3 σ limit of ${\rm log}(M_{\rm mol,[CII]}/{\rm {\rm M}_{\odot }}) < 9.3$. Together with radiative transfer calculations, we also investigated the possible cause of the dust poor nature of the GN-z11 showed by the blue color in the UV continuum of GN-z11 (βUV = −2.4), and found that ≳ 3 × deeper observations are crucial to study dust production at very high-redshift. Nevertheless, our observations show the crucial role of deep mm/submm observations of very high redshift galaxies to constrain multiple phases in the interstellar medium.