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2026ApJ...997..207L - Astrophys. J., 997, 207 (2026/February-1)

The Luminosity Function and Clustering of Hα Emitting Galaxies at z ≈ 4-6 from a Complete NIRCam Grism Redshift Survey.

LIN X., EGAMI E., SUN F., ZHANG H., FAN X., HELTON J.M., WANG F., BUNKER A.J., CAI Z., EISENSTEIN D.J., JAFFE D.T., JI Z., JIN X., PUDOKA M.A., TACCHELLA S., TEE W.L., RINALDI P., ROBERTSON B., SUN Y., WILLMER C.N.A., WILLOTT C., ZHANG J. and ZHU Y.

Abstract (from CDS):

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 ($\alpha =-1.8{7}_{-0.23}^{+0.30}$), 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 $0.05{0}_{-0.003}^{+0.002}\,{M}_{\odot }\,{{\rm{yr}}}^{-1}\,{{\rm{Mpc}}}^{-3}$ at 3.75 < z < 5 and $0.04{6}_{-0.004}^{+0.006}\,{M}_{\odot }\,{{\rm{yr}}}^{-1}\,{{\rm{Mpc}}}^{-3}$ 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 ${r}_{0}=4.6{1}_{-0.68}^{+1.00}\,{h}^{-1}\,\mathrm{Mpc}$ at z ≈ 4-5 and ${r}_{0}=6.2{3}_{-1.13}^{+1.68}\,{h}^{-1}{\rm{Mpc}}$ 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 ${\mathrm{log}}({M}_{h}/{M}_{\odot })=11.0-11.2$ at z ≈ 4-6, with a scatter of 0.4 dex.

Abstract Copyright: © 2026. The Author(s). Published by the American Astronomical Society.

Journal keyword(s): Star formation - High-redshift galaxy clusters - Protoclusters - Clustering - Luminosity function - Emission line galaxies

Simbad objects: 4

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