Insight into the starburst nature of Galaxy GN-z11 with JWST MIRI spectroscopy
/ Authors
J. 'Alvarez-M'arquez, A. G'omez, L. Colina, D. Langeroodi, R. Marques-Chaves, C. Prieto-Jim'enez, A. Bik, A. Alonso-Herrero, L. Boogaard, L. Costantin
and 14 more authors
M. Garc'ia-Mar'in, S. Gillman, J. Hjorth, E. Iani, I. Jermann, Á. Labiano, J. Melinder, R. Meyer, G. Ostlin, P. P'erez-Gonz'alez, P. Rinaldi, F. Walter, P. V. D. Werf, G. Wright
/ Abstract
This paper presents a deep MIRI/JWST medium-resolution spectroscopy (MRS) covering the rest-frame optical spectrum of the GN-z11 galaxy. The O,III 5008Å and Hα emission lines are detected and spectroscopically resolved. The line profiles are well modeled by a narrow Gaussian component with intrinsic full widths at half maximum of 189,±,25 and 231,±,52,km,s^-1, respectively. We do not find any evidence of a dominant broad Hα emission line component tracing a broad-line region in a type 1 active galactic nucleus (AGN). The existence of an accreting black hole dominating the optical continuum and emission lines of GN-z11 is not compatible with the measured Hα and O,III 5008Å luminosities. If the well-established relations for low-z AGNs apply in GN-z11, the O,III 5008Å and Hα luminosities would imply extremely high super-Eddington ratios E $>$,290), and bolometric luminosities ∼,20 times those derived from the UV/optical continuum. However, a broad (∼,430-470,km,s^-1) and weak ($<$,20-30%) Hα line component, tracing a minor AGN contribution in the optical, cannot be completely ruled out with the sensitivity of the current data. The physical and excitation properties of the ionized gas are consistent with a low-metallicity starburst with a star formation rate of 24,±,3,M_⊙,yr^-1. The electron temperature of the ionized gas is e (O^++),$=$,14000,±,2100,K, while the e gas-phase metallicity is 12,$+$,log(O/H),$=$,7.91,±,0.07 (Z,=,0.17,±,0.03,Z_⊙). The optical line ratios locate GN-z11 in the starburst or AGN region, but they are more consistent with those of local low-metallicity starbursts and high-z luminous galaxies detected at redshifts similar to GN-z11. We conclude that the MRS optical spectrum of GN-z11 is consistent with that of a massive, compact, and low-metallicity starburst galaxy. Its high star formation and stellar mass surface densities are close to those of the densest stellar clusters, and we therefore speculate that GN-z11 might undergo a feedback-free, highly efficient starburst phase. Additional JWST data are needed to validate this scenario and other recently proposed alternatives to explain the existence of bright compact galaxies in the early Universe.
Journal: Astronomy & Astrophysics