Kavli Affiliate: Kohei Inayoshi
| First 5 Authors: Zijian Zhang, Linhua Jiang, Weiyang Liu, Luis C. Ho, Kohei Inayoshi
| Summary:
James Webb Space Telescope (JWST) has revealed a population of red and
compact objects with a unique V-shape SED at z >= 4 known as Little Red Dots
(LRDs). Most of the LRDs with existing spectral observations exhibit broad
Balmer lines and are thus likely to host active galactic nuclei (AGNs). Here we
present a study of LRDs with no broad H-alpha component. Our sample consists of
five LRDs at z~5 with H-alpha line widths of about 250 km/s. They are selected
from 32 LRDs that have NIRSpec high- or medium-resolution grating spectra
covering H-alpha. During our construction of the sample, we find that
approximately 20 percent of the LRD candidates previously selected do not show
red continuum emission but resemble the V-shape spectra due to strong line
emission. Compared to normal star-forming galaxies, narrow-line LRDs tend to
have relatively higher H-alpha line widths and luminosities. If these LRDs are
dominated by galaxies, our SED modeling suggests that they are dusty, compact
star-forming galaxies with high stellar masses and star formation rates (SFRs).
Alternatively, if their SEDs are produced by AGNs, the inferred central black
hole masses (MBH) are in the range of 10^5 to 10^6 solar masses, placing them
at the low-mass end of the AGN population. They may represent an early stage of
super-Eddington growth, where the black holes have yet to accumulate
significant masses. With large measurement uncertainties, these black holes
appear slightly overmassive relative to the local MBH-Mstar relation, but
consistent or undermassive with respect to the MBH-sigma and MBH-Mdyn
relations. We further find that nearly half of the high-redshift broad-line
AGNs exhibit V-shape SEDs. (abridged)
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