Kavli Affiliate: Roberto Maiolino
| First 5 Authors: Junyu Zhang, Eiichi Egami, Fengwu Sun, Xiaojing Lin, Jianwei Lyu
| Summary:
We present a spectroscopic search for broad H$alpha$ emitters at z~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$alpha$
emitters with FWHM > 1000 km/s at z~4-5.5, including 9 new sources. The black
hole masses and AGN bolometric luminosities, inferred from the broad H$alpha$
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 red slope. 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$alpha$ 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.
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