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Abstract:

We present new MIRI F560W, F770W, and F1000W imaging of the galaxy GN-z11 at a redshift of 10.603. We report a significant detection (14 σ ) in the F560W and F770W images, and a marginal detection (3.2 σ ) in the F1000W filter. The new MIRI observations cover the optical-red spectral range and significantly extend previous NIRCam wavelength coverage from rest-frame 0.38 μm up to 0.86 μm. In this work, we analyse the spectral energy distribution (SED) combining this new MIRI imaging data with archival NIRSpec/Prism and MRS spectroscopy, and NIRCam imaging, i.e. covering the rest-frame 0.12–0.86 μm. New constraints such as the equivalent widths of the strong optical lines ([O  III ] λ 5008, H β and H α ) and the continuum emission at rest-frame 0.48 μm, 0.66 μm, and 0.86 μm, free of emission line contributions, are presented. The continuum emission shows a flat energy distribution, in f ν , up to 0.5 μm, compatible with the presence of a mixed stellar population of young (4 ± 1 Myr) and mature (63 ± 23 Myr) stars that also account for the [O  III ], H β , and H α emission lines. The continuum at rest-frame 0.66 μm shows a 36 ± 3% flux excess above the predicted flux for a mixed stellar population, pointing to the presence of an additional source contributing at these wavelengths. This excess increases to 91 ± 28% at rest-frame 0.86 μm, although with a large uncertainty due to the marginal detection in the F1000W filter. We consider that hot dust emission in the dusty torus around a type 2 active galactic nucleus (AGN) could be responsible for the observed excess. Alternatively, this excess could be due to hot dust emission or a photoluminiscence dust process (Extended Red Emission, ERE) under the extreme UV radiation field, as is observed in local metal-poor galaxies and in young compact starbursts. The presence of a type 1 AGN is not supported by the observed SED as the hot dust emission in luminous high- z quasi-stellar objects (QSOs) contributes at wavelengths above rest-frame 1 μm, and an additional ad hoc red source would be required to explain the observed flux excess at 0.66 and 0.86 μm. Additional deep MIRI imaging covering the rest-frame near-IR is needed to confirm the flux detection at 10 μm, and to discriminate between the different hot dust emission in the extreme starburst and AGN scenarios.

Abstract:

We study the luminosity function (LF) and clustering properties of 888 Hα emitters (HAEs) at 3.75 < z < 6 in the GOODS-N field. The sample, built from JWST CONGRESS and FRESCO NIRCam grism surveys using a novel redshift assignment algorithm, spans ∼62 arcmin2 and reaches LHα ∼ 1041.2 erg s−1. We identify two prominent filamentary protoclusters at z ≈ 4.41 and z ≈ 5.19, hosting 98 and 144 HAEs, respectively. The observed Hα LFs show similar shallow faint-end slopes for both protocluster and field galaxies at 3.75 < z < 5, and for the protocluster at 5 < z < 6 (α ≈ −1.2 to −1.3). In contrast, the field LF at 5 < z < 6 has a much steeper slope ( α=−1.87−0.23+0.30 ), suggesting that protocluster galaxies at z > 5 are more evolved, resembling the populations at 3.75 < z < 5. The observed star formation rate density from Hα integrated down to 0.45 M⊙ yr−1, is 0.050−0.003+0.002M⊙yr−1Mpc−3 at 3.75 < z < 5 and 0.046−0.004+0.006M⊙yr−1Mpc−3 at 5 < z < 6, with protoclusters contributing about 25% and 55%, respectively. This implies a large fraction of star formation at z > 4 occurs in protoclusters. For the first time, we conduct the star formation-rate-limited three-dimensional clustering analysis at z > 4. We find that the filamentary geometry of protoclusters flattens the power-law shape of the HAE autocorrelation functions, with slopes much shallower than the typically assumed value. The autocorrelation function of field HAEs has a correlation length of r0=4.61−0.68+1.00h−1Mpc at z ≈ 4−5 and r0=6.23−1.13+1.68h−1Mpc at z ≈ 5−6. Comparing the observed correlation functions with the UniverseMachine simulation, we infer the dark matter (sub-)halo masses of HAEs to be log(Mh/M⊙)=11.0−11.2 at z ≈ 4−6, with a scatter of 0.4 dex.