Abundant Population of Broad H$α$ Emitters in the GOODS-N Field Revealed by CONGRESS, FRESCO, and JADES

Junyu Zhang, Eiichi Egami, Fengwu Sun, Xiaojing Lin, Jianwei Lyu, Yongda Zhu, Pierluigi Rinaldi, Yang Sun, Andrew J. Bunker, Rachana Bhatawdekar, Jakob M. Helton, Roberto Maiolino, Zheng Ma, Brant Robertson, Sandro Tacchella, Giacomo Venturi, Christina C. Williams, Chris Willott

First listed 2025-05-05 | Last updated 2026-01-13

Abstract

We present a spectroscopic search for broad H$α$ emitters at z$\approx$3.7-6.5 in the GOODS-N field, utilizing JWST/NIRCam slitless spectroscopy from FRESCO and CONGRESS, complemented by JADES imaging. We identify 19 broad H$α$ emitters with FWHM$>$1000 km/s at z$\approx$4-5.5, including 9 new sources. The broad H$α$ luminosity function (LF) derived from our sample is consistent with those of other JWST-selected broad-line AGN reported in the literature. The black hole masses and AGN bolometric luminosities, inferred from the broad H$α$ components, indicate that most sources are accreting at ~10% of the Eddington limit. We derive their host stellar masses via SED fitting and find higher $M_{BH}/M_{*}$ ratios relative to the local $M_{BH}-M_{*}$ relations, consistent with previous studies. We find that 42% of the sample do not satisfy the widely-used color selection criteria for Little Red Dots (LRDs), with the majority of these sources lacking the characteristic steep rest-optical red slope, indicating that the LRD selection is highly incomplete when selecting AGN galaxies. A comparison of the average SEDs between our sample and LRDs selected in the same field reveals that the steep red slopes observed in some LRDs are likely due to line-boosting effects as previously suggested. Furthermore, we find that 68% of color-selected LRDs with H$α$ detections in the NIRCam/Grism spectra do not exhibit broad-line features. While the limited sensitivity of the grism spectra may hinder the detection of broad-line components in faint sources, our findings still highlight the enigmatic nature of the LRD population.

Short digest

Using JWST/NIRCam WFSS from FRESCO and CONGRESS plus JADES imaging, the authors conduct a GOODS‑N search for broad Hα at z≈3.7–6.5 and confirm 19 emitters at z≈4–5.5, including nine new ones. Their broad Hα LF aligns with other JWST BLAGN results, and virial BH masses with bolometric corrections imply ≈0.1 Eddington accretion and elevated MBH/M* relative to local relations. Color comparisons show LRD cuts miss 42% of these spectroscopic AGN—many lack the steep rest‑optical red slope—and average SEDs indicate some LRD red slopes are line‑boosted. Notably, 68% of color‑selected LRDs with Hα detections lack broad lines in the grism data, potentially due to sensitivity limits, underscoring the LRD population’s mixed nature.

Key figures to inspect

• Figure 1: Inspect the multi-component Hα+[N II] fits source-by-source to verify the broad Hα component (FWHM>1000 km/s), the relative narrow/broad decomposition, and residuals that establish BLR detections.
• Figure 2: Use the false‑color stamps to judge compactness and rest‑color diversity across the 19 AGN; compare F444W vs F356W emphasis (FRESCO vs CONGRESS) to see which objects lack the very red rest‑optical slopes typical of color‑selected LRDs.
• Figure 3: Check the spatial distribution of confirmed broad‑line AGN against the JADES/FRESCO/CONGRESS footprints and redshift color‑coding to assess survey coverage and any apparent clustering within GOODS‑N.
• Figure 4: Examine [O III] profiles for the three showcased objects to confirm the absence of comparably broad [O III] wings—supporting that line broadening is from the BLR in Hα rather than strong NLR outflows—and to validate systemic redshifts used in Hα modeling.